[PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alan Maguire]

v1.25 of pahole supports filtering out functions with multiple
inconsistent function prototypes or optimized-out parameters
from the BTF representation.  These present problems because
there is no additional info in BTF saying which inconsistent
prototype matches which function instance to help guide
attachment, and functions with optimized-out parameters can
lead to incorrect assumptions about register contents.

So for now, filter out such functions while adding BTF
representations for functions that have "."-suffixes
(foo.isra.0) but not optimized-out parameters.

This patch assumes changes in [1] land and pahole is bumped
to v1.25.

[1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

---
 scripts/pahole-flags.sh | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
index 1f1f1d3..728d551 100755
--- a/scripts/pahole-flags.sh
+++ b/scripts/pahole-flags.sh
@@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
 	# see PAHOLE_HAS_LANG_EXCLUDE
 	extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
 fi
+if [ "${pahole_ver}" -ge "125" ]; then
+	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
+fi
 
 echo ${extra_paholeopt}
-- 
1.8.3.1

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Thu, Feb 09, 2023 at 01:28:51PM +0000, Alan Maguire wrote:
> v1.25 of pahole supports filtering out functions with multiple
> inconsistent function prototypes or optimized-out parameters
> from the BTF representation.  These present problems because
> there is no additional info in BTF saying which inconsistent
> prototype matches which function instance to help guide
> attachment, and functions with optimized-out parameters can
> lead to incorrect assumptions about register contents.
> 
> So for now, filter out such functions while adding BTF
> representations for functions that have "."-suffixes
> (foo.isra.0) but not optimized-out parameters.
> 
> This patch assumes changes in [1] land and pahole is bumped
> to v1.25.
> 
> [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> 
> ---
>  scripts/pahole-flags.sh | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> index 1f1f1d3..728d551 100755
> --- a/scripts/pahole-flags.sh
> +++ b/scripts/pahole-flags.sh
> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>  	# see PAHOLE_HAS_LANG_EXCLUDE
>  	extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>  fi
> +if [ "${pahole_ver}" -ge "125" ]; then
> +	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> +fi
>  
>  echo ${extra_paholeopt}
> -- 
> 1.8.3.1
> 

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Thu,  9 Feb 2023 13:28:51 +0000 you wrote:
> v1.25 of pahole supports filtering out functions with multiple
> inconsistent function prototypes or optimized-out parameters
> from the BTF representation.  These present problems because
> there is no additional info in BTF saying which inconsistent
> prototype matches which function instance to help guide
> attachment, and functions with optimized-out parameters can
> lead to incorrect assumptions about register contents.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25
    https://git.kernel.org/bpf/bpf-next/c/0243d3dfe274

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alexei Starovoitov]

On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> v1.25 of pahole supports filtering out functions with multiple
> inconsistent function prototypes or optimized-out parameters
> from the BTF representation.  These present problems because
> there is no additional info in BTF saying which inconsistent
> prototype matches which function instance to help guide
> attachment, and functions with optimized-out parameters can
> lead to incorrect assumptions about register contents.
>
> So for now, filter out such functions while adding BTF
> representations for functions that have "."-suffixes
> (foo.isra.0) but not optimized-out parameters.
>
> This patch assumes changes in [1] land and pahole is bumped
> to v1.25.
>
> [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>
> ---
>  scripts/pahole-flags.sh | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> index 1f1f1d3..728d551 100755
> --- a/scripts/pahole-flags.sh
> +++ b/scripts/pahole-flags.sh
> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>         # see PAHOLE_HAS_LANG_EXCLUDE
>         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>  fi
> +if [ "${pahole_ver}" -ge "125" ]; then
> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> +fi

We landed this too soon.
#229     tracing_struct:FAIL
is failing now.
since bpf_testmod.ko is missing a bunch of functions though they're global.

I've tried a bunch of different flags and attributes, but none of them
helped.
The only thing that works is:
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 46500636d8cd..5fd0f75d5d20 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
        long b;
 };

+__attribute__((optimize("-O0")))
 noinline int
 bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
b, int c) {

We cannot do:
--- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
+++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
@@ -10,7 +10,7 @@ endif
 MODULES = bpf_testmod.ko

 obj-m += bpf_testmod.o
-CFLAGS_bpf_testmod.o = -I$(src)
+CFLAGS_bpf_testmod.o = -I$(src) -O0

The build fails due to asm stuff.

Maybe we should make scripts/pahole-flags.sh selective
and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?

Thoughts?

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alexei Starovoitov]

On Mon, Feb 13, 2023 at 7:12 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> >
> > v1.25 of pahole supports filtering out functions with multiple
> > inconsistent function prototypes or optimized-out parameters
> > from the BTF representation.  These present problems because
> > there is no additional info in BTF saying which inconsistent
> > prototype matches which function instance to help guide
> > attachment, and functions with optimized-out parameters can
> > lead to incorrect assumptions about register contents.
> >
> > So for now, filter out such functions while adding BTF
> > representations for functions that have "."-suffixes
> > (foo.isra.0) but not optimized-out parameters.
> >
> > This patch assumes changes in [1] land and pahole is bumped
> > to v1.25.
> >
> > [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
> >
> > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> >
> > ---
> >  scripts/pahole-flags.sh | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > index 1f1f1d3..728d551 100755
> > --- a/scripts/pahole-flags.sh
> > +++ b/scripts/pahole-flags.sh
> > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> >         # see PAHOLE_HAS_LANG_EXCLUDE
> >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> >  fi
> > +if [ "${pahole_ver}" -ge "125" ]; then
> > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > +fi
>
> We landed this too soon.
> #229     tracing_struct:FAIL
> is failing now.
> since bpf_testmod.ko is missing a bunch of functions though they're global.
>
> I've tried a bunch of different flags and attributes, but none of them
> helped.
> The only thing that works is:
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 46500636d8cd..5fd0f75d5d20 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
>         long b;
>  };
>
> +__attribute__((optimize("-O0")))
>  noinline int
>  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
> b, int c) {
>
> We cannot do:
> --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
> +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
> @@ -10,7 +10,7 @@ endif
>  MODULES = bpf_testmod.ko
>
>  obj-m += bpf_testmod.o
> -CFLAGS_bpf_testmod.o = -I$(src)
> +CFLAGS_bpf_testmod.o = -I$(src) -O0
>
> The build fails due to asm stuff.
>
> Maybe we should make scripts/pahole-flags.sh selective
> and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
>
> Thoughts?

It's even worse with clang compiled kernel:
    WARN: resolve_btfids: unresolved symbol tcp_reno_cong_avoid
    WARN: resolve_btfids: unresolved symbol dctcp_update_alpha
    WARN: resolve_btfids: unresolved symbol cubictcp_cong_avoid
    WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_timestamp
    WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_hash
    WARN: resolve_btfids: unresolved symbol bpf_task_kptr_get
    WARN: resolve_btfids: unresolved symbol bpf_task_acquire_not_zero
    WARN: resolve_btfids: unresolved symbol bpf_rdonly_cast
    WARN: resolve_btfids: unresolved symbol
bpf_kfunc_call_test_static_unused_arg
    WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_ref

so I reverted this commit for now.
Looks like pahole with skip_encoding_btf_inconsistent_proto needs
to be more accurate.
It's way too aggressive removing valid functions.

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Mon, Feb 13, 2023 at 07:12:33PM -0800, Alexei Starovoitov wrote:
> On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> >
> > v1.25 of pahole supports filtering out functions with multiple
> > inconsistent function prototypes or optimized-out parameters
> > from the BTF representation.  These present problems because
> > there is no additional info in BTF saying which inconsistent
> > prototype matches which function instance to help guide
> > attachment, and functions with optimized-out parameters can
> > lead to incorrect assumptions about register contents.
> >
> > So for now, filter out such functions while adding BTF
> > representations for functions that have "."-suffixes
> > (foo.isra.0) but not optimized-out parameters.
> >
> > This patch assumes changes in [1] land and pahole is bumped
> > to v1.25.
> >
> > [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
> >
> > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> >
> > ---
> >  scripts/pahole-flags.sh | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > index 1f1f1d3..728d551 100755
> > --- a/scripts/pahole-flags.sh
> > +++ b/scripts/pahole-flags.sh
> > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> >         # see PAHOLE_HAS_LANG_EXCLUDE
> >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> >  fi
> > +if [ "${pahole_ver}" -ge "125" ]; then
> > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > +fi
> 
> We landed this too soon.
> #229     tracing_struct:FAIL
> is failing now.
> since bpf_testmod.ko is missing a bunch of functions though they're global.
> 

hum, didn't see this one failing.. I'll try that again

jirka

> I've tried a bunch of different flags and attributes, but none of them
> helped.
> The only thing that works is:
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 46500636d8cd..5fd0f75d5d20 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
>         long b;
>  };
> 
> +__attribute__((optimize("-O0")))
>  noinline int
>  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
> b, int c) {
> 
> We cannot do:
> --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
> +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
> @@ -10,7 +10,7 @@ endif
>  MODULES = bpf_testmod.ko
> 
>  obj-m += bpf_testmod.o
> -CFLAGS_bpf_testmod.o = -I$(src)
> +CFLAGS_bpf_testmod.o = -I$(src) -O0
> 
> The build fails due to asm stuff.
> 
> Maybe we should make scripts/pahole-flags.sh selective
> and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
> 
> Thoughts?

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Arnaldo Carvalho de Melo]

Em Tue, Feb 14, 2023 at 01:27:43PM +0100, Jiri Olsa escreveu:
> On Mon, Feb 13, 2023 at 07:12:33PM -0800, Alexei Starovoitov wrote:
> > On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> > >
> > > v1.25 of pahole supports filtering out functions with multiple
> > > inconsistent function prototypes or optimized-out parameters
> > > from the BTF representation.  These present problems because
> > > there is no additional info in BTF saying which inconsistent
> > > prototype matches which function instance to help guide
> > > attachment, and functions with optimized-out parameters can
> > > lead to incorrect assumptions about register contents.
> > >
> > > So for now, filter out such functions while adding BTF
> > > representations for functions that have "."-suffixes
> > > (foo.isra.0) but not optimized-out parameters.
> > >
> > > This patch assumes changes in [1] land and pahole is bumped
> > > to v1.25.
> > >
> > > [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
> > >
> > > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > > Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > >
> > > ---
> > >  scripts/pahole-flags.sh | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > > index 1f1f1d3..728d551 100755
> > > --- a/scripts/pahole-flags.sh
> > > +++ b/scripts/pahole-flags.sh
> > > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > >         # see PAHOLE_HAS_LANG_EXCLUDE
> > >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > >  fi
> > > +if [ "${pahole_ver}" -ge "125" ]; then
> > > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > > +fi
> > 
> > We landed this too soon.
> > #229     tracing_struct:FAIL
> > is failing now.
> > since bpf_testmod.ko is missing a bunch of functions though they're global.
> > 
> 
> hum, didn't see this one failing.. I'll try that again

/me too, redoing tests her, with gcc and clang, running selftests on a
system booted with a kernel built with pahole 1.25, etc.

- Arnaldo
 
> jirka
> 
> > I've tried a bunch of different flags and attributes, but none of them
> > helped.
> > The only thing that works is:
> > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > index 46500636d8cd..5fd0f75d5d20 100644
> > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
> >         long b;
> >  };
> > 
> > +__attribute__((optimize("-O0")))
> >  noinline int
> >  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
> > b, int c) {
> > 
> > We cannot do:
> > --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > @@ -10,7 +10,7 @@ endif
> >  MODULES = bpf_testmod.ko
> > 
> >  obj-m += bpf_testmod.o
> > -CFLAGS_bpf_testmod.o = -I$(src)
> > +CFLAGS_bpf_testmod.o = -I$(src) -O0
> > 
> > The build fails due to asm stuff.
> > 
> > Maybe we should make scripts/pahole-flags.sh selective
> > and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
> > 
> > Thoughts?

-- 

- Arnaldo

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Tue, Feb 14, 2023 at 01:17:56PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Feb 14, 2023 at 01:27:43PM +0100, Jiri Olsa escreveu:
> > On Mon, Feb 13, 2023 at 07:12:33PM -0800, Alexei Starovoitov wrote:
> > > On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> > > >
> > > > v1.25 of pahole supports filtering out functions with multiple
> > > > inconsistent function prototypes or optimized-out parameters
> > > > from the BTF representation.  These present problems because
> > > > there is no additional info in BTF saying which inconsistent
> > > > prototype matches which function instance to help guide
> > > > attachment, and functions with optimized-out parameters can
> > > > lead to incorrect assumptions about register contents.
> > > >
> > > > So for now, filter out such functions while adding BTF
> > > > representations for functions that have "."-suffixes
> > > > (foo.isra.0) but not optimized-out parameters.
> > > >
> > > > This patch assumes changes in [1] land and pahole is bumped
> > > > to v1.25.
> > > >
> > > > [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
> > > >
> > > > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > > > Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > > >
> > > > ---
> > > >  scripts/pahole-flags.sh | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > > > index 1f1f1d3..728d551 100755
> > > > --- a/scripts/pahole-flags.sh
> > > > +++ b/scripts/pahole-flags.sh
> > > > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > > >         # see PAHOLE_HAS_LANG_EXCLUDE
> > > >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > > >  fi
> > > > +if [ "${pahole_ver}" -ge "125" ]; then
> > > > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > > > +fi
> > > 
> > > We landed this too soon.
> > > #229     tracing_struct:FAIL
> > > is failing now.
> > > since bpf_testmod.ko is missing a bunch of functions though they're global.
> > > 
> > 
> > hum, didn't see this one failing.. I'll try that again
> 
> /me too, redoing tests her, with gcc and clang, running selftests on a
> system booted with a kernel built with pahole 1.25, etc.

ok, can't see that with gcc, but reproduced with clang 16

resolve_btfids complains because those functions are not in btf

  BTFIDS  vmlinux
WARN: resolve_btfids: unresolved symbol tcp_reno_cong_avoid
WARN: resolve_btfids: unresolved symbol should_failslab
WARN: resolve_btfids: unresolved symbol should_fail_alloc_page
WARN: resolve_btfids: unresolved symbol cubictcp_cong_avoid
WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_timestamp
WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_hash
WARN: resolve_btfids: unresolved symbol bpf_task_kptr_get
WARN: resolve_btfids: unresolved symbol bpf_task_acquire_not_zero
WARN: resolve_btfids: unresolved symbol bpf_rdonly_cast
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_static_unused_arg
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_ref
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_pass_ctx
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_pass2
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_pass1
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_mem_len_pass1
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_mem_len_fail2
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_mem_len_fail1
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_kptr_get
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_fail3
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_fail2
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_fail1
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_acquire
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test2
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test1
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_memb_release
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_memb1_release
WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_int_mem_release
  NM      System.map

jirka

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alan Maguire]

On 14/02/2023 22:12, Jiri Olsa wrote:
> On Tue, Feb 14, 2023 at 01:17:56PM -0300, Arnaldo Carvalho de Melo wrote:
>> Em Tue, Feb 14, 2023 at 01:27:43PM +0100, Jiri Olsa escreveu:
>>> On Mon, Feb 13, 2023 at 07:12:33PM -0800, Alexei Starovoitov wrote:
>>>> On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>>>>
>>>>> v1.25 of pahole supports filtering out functions with multiple
>>>>> inconsistent function prototypes or optimized-out parameters
>>>>> from the BTF representation.  These present problems because
>>>>> there is no additional info in BTF saying which inconsistent
>>>>> prototype matches which function instance to help guide
>>>>> attachment, and functions with optimized-out parameters can
>>>>> lead to incorrect assumptions about register contents.
>>>>>
>>>>> So for now, filter out such functions while adding BTF
>>>>> representations for functions that have "."-suffixes
>>>>> (foo.isra.0) but not optimized-out parameters.
>>>>>
>>>>> This patch assumes changes in [1] land and pahole is bumped
>>>>> to v1.25.
>>>>>
>>>>> [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
>>>>>
>>>>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>>>>> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>>>>>
>>>>> ---
>>>>>  scripts/pahole-flags.sh | 3 +++
>>>>>  1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>>>>> index 1f1f1d3..728d551 100755
>>>>> --- a/scripts/pahole-flags.sh
>>>>> +++ b/scripts/pahole-flags.sh
>>>>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>>>>         # see PAHOLE_HAS_LANG_EXCLUDE
>>>>>         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>>>>  fi
>>>>> +if [ "${pahole_ver}" -ge "125" ]; then
>>>>> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
>>>>> +fi
>>>>
>>>> We landed this too soon.
>>>> #229     tracing_struct:FAIL
>>>> is failing now.
>>>> since bpf_testmod.ko is missing a bunch of functions though they're global.
>>>>
>>>
>>> hum, didn't see this one failing.. I'll try that again
>>
>> /me too, redoing tests her, with gcc and clang, running selftests on a
>> system booted with a kernel built with pahole 1.25, etc.
> 
> ok, can't see that with gcc, but reproduced with clang 16
> 
> resolve_btfids complains because those functions are not in btf
> 
>   BTFIDS  vmlinux
> WARN: resolve_btfids: unresolved symbol tcp_reno_cong_avoid
> WARN: resolve_btfids: unresolved symbol should_failslab
> WARN: resolve_btfids: unresolved symbol should_fail_alloc_page
> WARN: resolve_btfids: unresolved symbol cubictcp_cong_avoid
> WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_timestamp
> WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_hash
> WARN: resolve_btfids: unresolved symbol bpf_task_kptr_get
> WARN: resolve_btfids: unresolved symbol bpf_task_acquire_not_zero
> WARN: resolve_btfids: unresolved symbol bpf_rdonly_cast
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_static_unused_arg
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_ref
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_pass_ctx
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_pass2
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_pass1
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_mem_len_pass1
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_mem_len_fail2
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_mem_len_fail1
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_kptr_get
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_fail3
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_fail2
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_fail1
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_acquire
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test2
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test1
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_memb_release
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_memb1_release
> WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_int_mem_release
>   NM      System.map
>

Jiri kindly provided a clang-generated vmlinux, and I also managed to reproduce
issues by building the kernel with clang 17.

The first question is if we're detecting optimizations correctly. From
an initial look, I _think_ we are, in some cases at least.

For tcp_reno_cong_avoid(), the function signature is

__bpf_kfunc void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)

...but our handling of the DWARF generated spots that the "ack" parameter
has no location info; and looking at the source it is never used.  Here is 
the DWARF - note no location info for the second parameter ("ack"):

0x0891dab0:   DW_TAG_subprogram
                DW_AT_low_pc    (0xffffffff82031180)
                DW_AT_high_pc   (0xffffffff820311d8)
                DW_AT_frame_base        (DW_OP_reg7 RSP)
                DW_AT_call_all_calls    (true)
                DW_AT_name      ("tcp_reno_cong_avoid")
                DW_AT_decl_file ("/home/jolsa/kernel/linux-qemu/net/ipv4/tcp_cong.c")
                DW_AT_decl_line (446)
                DW_AT_prototyped        (true)
                DW_AT_external  (true)

0x0891dabe:     DW_TAG_formal_parameter
                  DW_AT_location        (indexed (0x7a) loclist = 0x00f50eb1:
                     [0xffffffff82031185, 0xffffffff8203119e): DW_OP_reg5 RDI
                     [0xffffffff8203119e, 0xffffffff820311cc): DW_OP_reg3 RBX
                     [0xffffffff820311cc, 0xffffffff820311d1): DW_OP_reg5 RDI
                     [0xffffffff820311d1, 0xffffffff820311d2): DW_OP_reg3 RBX
                     [0xffffffff820311d2, 0xffffffff820311d8): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value)
                  DW_AT_name    ("sk")
                  DW_AT_decl_file       ("/home/jolsa/kernel/linux-qemu/net/ipv4/tcp_cong.c")
                  DW_AT_decl_line       (446)
                  DW_AT_type    (0x08902c4d "sock *")

0x0891dac9:     DW_TAG_formal_parameter
                  DW_AT_name    ("ack")
                  DW_AT_decl_file       ("/home/jolsa/kernel/linux-qemu/net/ipv4/tcp_cong.c")
                  DW_AT_decl_line       (446)
                  DW_AT_type    (0x08902c3d "u32")

0x0891dad4:     DW_TAG_formal_parameter
                  DW_AT_location        (indexed (0x7b) loclist = 0x00f50eda:
                     [0xffffffff82031185, 0xffffffff820311bc): DW_OP_reg1 RDX
                     [0xffffffff820311bc, 0xffffffff820311c8): DW_OP_reg0 RAX
                     [0xffffffff820311c8, 0xffffffff820311d1): DW_OP_reg1 RDX)
                  DW_AT_name    ("acked")
                  DW_AT_decl_file       ("/home/jolsa/kernel/linux-qemu/net/ipv4/tcp_cong.c")
                  DW_AT_decl_line       (446)
                  DW_AT_type    (0x08902c3d "u32")

Disassembling we see the following:

(gdb) disassemble/s tcp_reno_cong_avoid
Dump of assembler code for function tcp_reno_cong_avoid:
net/ipv4/tcp_cong.c:
447	{
   0xffffffff82031180 <+0>:	nopl   0x0(%rax,%rax,1)
   0xffffffff82031185 <+5>:	push   %rbx
   0xffffffff82031186 <+6>:	mov    %rdi,%rbx

./include/net/tcp.h:
1305		if (tp->is_cwnd_limited)
   0xffffffff82031189 <+9>:	cmpb   $0x0,0x95f(%rdi)
   0xffffffff82031190 <+16>:	mov    0x9e4(%rdi),%eax
   0xffffffff82031196 <+22>:	mov    0x9e8(%rdi),%esi
   0xffffffff8203119c <+28>:	js     0xffffffff820311ae <tcp_reno_cong_avoid+46>

1238		return tcp_snd_cwnd(tp) < tp->snd_ssthresh;
   0xffffffff8203119e <+30>:	cmp    %eax,%esi

1306			return true;
1307	
1308		/* If in slow start, ensure cwnd grows to twice what was ACKed. */
1309		if (tcp_in_slow_start(tp))
   0xffffffff820311a0 <+32>:	jae    0xffffffff820311d1 <tcp_reno_cong_avoid+81>

1310			return tcp_snd_cwnd(tp) < 2 * tp->max_packets_out;
   0xffffffff820311a2 <+34>:	mov    0x9b4(%rbx),%ecx
   0xffffffff820311a8 <+40>:	add    %ecx,%ecx
   0xffffffff820311aa <+42>:	cmp    %ecx,%esi

net/ipv4/tcp_cong.c:
450		if (!tcp_is_cwnd_limited(sk))
   0xffffffff820311ac <+44>:	jae    0xffffffff820311d1 <tcp_reno_cong_avoid+81>

./include/net/tcp.h:
1238		return tcp_snd_cwnd(tp) < tp->snd_ssthresh;
   0xffffffff820311ae <+46>:	cmp    %eax,%esi

net/ipv4/tcp_cong.c:
454		if (tcp_in_slow_start(tp)) {
   0xffffffff820311b0 <+48>:	jae    0xffffffff820311c8 <tcp_reno_cong_avoid+72>

455			acked = tcp_slow_start(tp, acked);
   0xffffffff820311b2 <+50>:	mov    %rbx,%rdi
   0xffffffff820311b5 <+53>:	mov    %edx,%esi
   0xffffffff820311b7 <+55>:	call   0xffffffff82031080 <tcp_slow_start>

--Type <RET> for more, q to quit, c to continue without paging--
456			if (!acked)
   0xffffffff820311bc <+60>:	test   %eax,%eax
   0xffffffff820311be <+62>:	je     0xffffffff820311d1 <tcp_reno_cong_avoid+81>
   0xffffffff820311c0 <+64>:	mov    %eax,%edx

./include/net/tcp.h:
1227		return tp->snd_cwnd;
   0xffffffff820311c2 <+66>:	mov    0x9e8(%rbx),%esi

net/ipv4/tcp_cong.c:
460		tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
   0xffffffff820311c8 <+72>:	mov    %rbx,%rdi
   0xffffffff820311cb <+75>:	pop    %rbx
   0xffffffff820311cc <+76>:	jmp    0xffffffff820310d0 <tcp_cong_avoid_ai>

461	}
   0xffffffff820311d1 <+81>:	pop    %rbx
   0xffffffff820311d2 <+82>:	cs jmp 0xffffffff8223c240 <__x86_return_thunk>
End of assembler dump.

From what I can see above - unless I'm misreading it - we see something
interesting here. Note that in preparing the call to tcp_cong_avoid_ai(),
we get the tcp_snd_cwnd() value into %esi, but nothing needs to be done with 
%rdx because it's already got the "acked" value in it. Now this is good
news, because if we're calling this kfunc - that only uses the first and
third parameters - preparing all three will not lead to any nasty surprises
(we just wasted a bit of time preparing the second unused parameter).
If this held true for all kfuncs it would mean that skipping representing
them in BTF due to optimized-out parameters would be the wrong answer.
The key thing to figure out is this - if we optimize out a parameter, will
the subsequent parameters that are not optimized out still use the registers
that they would be expected to if no optimization had happened? So if I 
optimize out the first parameter say, will the second parameter use the 
"right" register (%rsi on x86_64)? If that were guaranteed, we could relax
the cases where we skip BTF generation to the following:

1. cases where multiple inconsistent function prototypes for the same name
   exist.
2. cases where a function has multiple instances with different optimization
   states (optimized out parameter in one CU but not another). This is another
   instance of 1 really, and shouldn't be an issue for kfuncs.
3. cases where an optimized-out parameter has knock-on effects for the
   registers used to handle other unoptimized parameters such that assumptions
   we would make from the function signature are violated for non-optimized out
   parameters. So the parameter would be flagged as using an unexpected
   register, and that unexpected case would instead lead to skipping BTF
   encoding.

I can have a go at implementing the above in pahole and seeing how it effects
our list of functions.

Note though that what's good for kfuncs isn't necessarily good for tracing
accuracy; if assumptions I make about parameter presence are violated, I will
see strange trace results based upon reading the code, whereas if I am
preparing kfunc parameters, a bit of extra work is done preparing an unused
parameter, but no harm is done. For the tracing case, function annotations
flagging optimized-out parameters via BTF tags could help.

However, none of the above will help problematic cases like
bpf_xdp_metadata_rx_timestamp() or bpf_xdp_metadata_rx_hash(); 
again we see missing location info in their DWARF representations

0x07449011:   DW_TAG_subprogram
                DW_AT_low_pc    (0xffffffff81ec8c80)
                DW_AT_high_pc   (0xffffffff81ec8c90)
                DW_AT_frame_base        (DW_OP_reg7 RSP)
                DW_AT_call_all_calls    (true)
                DW_AT_name      ("bpf_xdp_metadata_rx_timestamp")
                DW_AT_decl_file ("/home/jolsa/kernel/linux-qemu/net/core/xdp.c")
                DW_AT_decl_line (725)
                DW_AT_prototyped        (true)
                DW_AT_type      (0x0742f1ae "int")
                DW_AT_external  (true)

0x07449023:     DW_TAG_formal_parameter
                  DW_AT_name    ("ctx")
                  DW_AT_decl_file       ("/home/jolsa/kernel/linux-qemu/net/core/xdp.c")
                  DW_AT_decl_line       (725)
                  DW_AT_type    (0x0743dff0 "const xdp_md *")

0x0744902d:     DW_TAG_formal_parameter
                  DW_AT_name    ("timestamp")
                  DW_AT_decl_file       ("/home/jolsa/kernel/linux-qemu/net/core/xdp.c")
                  DW_AT_decl_line       (725)
                  DW_AT_type    (0x0743217a "u64 *")


...due to the function just being a "return -EOPNOTSUPP;":

Dump of assembler code for function bpf_xdp_metadata_rx_timestamp:
   0xffffffff81ec8c80 <+0>:	nopl   0x0(%rax,%rax,1)
   0xffffffff81ec8c85 <+5>:	mov    $0xffffffa1,%eax
   0xffffffff81ec8c8a <+10>:	cs jmp 0xffffffff8223c240 <__x86_return_thunk>
End of assembler dump.

__bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
{
        return -EOPNOTSUPP;
}

...and playing around with various attributes here does not seem to help.

should_failslab() has a similar story, I suspect because __should_failslab()
got optimized out due to CONFIG_FAILSLAB=n and we get

(gdb) disassemble/s should_failslab
Dump of assembler code for function should_failslab:
mm/slab_common.c:
1462	{
   0xffffffff81422490 <+0>:	nopl   0x0(%rax,%rax,1)

1463		if (__should_failslab(s, gfpflags))
1464			return -ENOMEM;
1465		return 0;
1466	}
   0xffffffff81422495 <+5>:	xor    %eax,%eax
   0xffffffff81422497 <+7>:	cs jmp 0xffffffff8223c240 <__x86_return_thunk>
End of assembler dump.

However, the caller of this function still prepares parameters as if
they were going to be used:

(gdb) disassemble slab_pre_alloc_hook
Dump of assembler code for function slab_pre_alloc_hook:
   0xffffffff813bc5b0 <+0>:	push   %rbp
   0xffffffff813bc5b1 <+1>:	mov    %rsp,%rbp
   0xffffffff813bc5b4 <+4>:	push   %r15
   0xffffffff813bc5b6 <+6>:	push   %r14
   0xffffffff813bc5b8 <+8>:	push   %r13
   0xffffffff813bc5ba <+10>:	push   %r12
   0xffffffff813bc5bc <+12>:	push   %rbx
   0xffffffff813bc5bd <+13>:	sub    $0x20,%rsp
   0xffffffff813bc5c1 <+17>:	mov    %r8d,%r15d
   0xffffffff813bc5c4 <+20>:	mov    %rcx,%r12
   0xffffffff813bc5c7 <+23>:	mov    %rdx,-0x48(%rbp)
   0xffffffff813bc5cb <+27>:	mov    %rsi,%rbx
   0xffffffff813bc5ce <+30>:	mov    %rdi,%r13
   0xffffffff813bc5d1 <+33>:	and    0x219ff00(%rip),%r15d        # 0xffffffff8355c4d8 <gfp_allowed_mask>
   0xffffffff813bc5d8 <+40>:	test   $0x400,%r15d
   0xffffffff813bc5df <+47>:	je     0xffffffff813bc5e6 <slab_pre_alloc_hook+54>
   0xffffffff813bc5e1 <+49>:	callq  0xffffffff81d27b68 <__SCT__might_resched>
   0xffffffff813bc5e6 <+54>:	mov    %r13,%rdi
   0xffffffff813bc5e9 <+57>:	mov    %r15d,%esi
   0xffffffff813bc5ec <+60>:	callq  0xffffffff81340a70 <should_failslab>

...so the function is still being called with the right register
values. This points to a conceptual flaw in the approach I was
taking - we cannot equate register _state_ on entry to a function
with register _use_ by that function. So from a DWARF perspective,
the fact that there is no location information does not necessarily
tell us the function is not _called_ with that parameter; rather it 
tells us it is not used within the body of the function.

This all combines to suggest that the only time we should be
definitive in rejecting a function for BTF encoding due to 
optimizations is when they interfere with the expectations we
have about _used_ parameter->register mappings. So concretely,
where the second parameter uses a register other than the
one the calling conventions dictate should be used by the 
second parameter say, or indeed does not use a register at
all. It is possible that we could be more definitive by examining
DWARF call site info, but there is none for some of the above
functions like should_failslab(), so that will not help here
as far as I can see.

Does this seem reasonable, or am I missing something here?
I'm worried we're going to end up playing whack-a-mole with
increasingly clever compiler optimizations, so my instinct
is that we need to be conservative in choosing when to skip
BTF encoding, only doing so when we are certain it will mislead
badly. I _think_ there is some justification to that based on
the above. What do you think?

Alan

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Arnaldo Carvalho de Melo]

Em Mon, Feb 13, 2023 at 10:09:21PM -0800, Alexei Starovoitov escreveu:
> On Mon, Feb 13, 2023 at 7:12 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> > > +++ b/scripts/pahole-flags.sh
> > > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > >         # see PAHOLE_HAS_LANG_EXCLUDE
> > >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > >  fi
> > > +if [ "${pahole_ver}" -ge "125" ]; then
> > > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > > +fi
> >
> > We landed this too soon.
> > #229     tracing_struct:FAIL
> > is failing now.
> > since bpf_testmod.ko is missing a bunch of functions though they're global.
> >
> > I've tried a bunch of different flags and attributes, but none of them
> > helped.
> > The only thing that works is:
> > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > index 46500636d8cd..5fd0f75d5d20 100644
> > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
> >         long b;
> >  };
> >
> > +__attribute__((optimize("-O0")))
> >  noinline int
> >  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
> > b, int c) {
> >
> > We cannot do:
> > --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > @@ -10,7 +10,7 @@ endif
> >  MODULES = bpf_testmod.ko
> >
> >  obj-m += bpf_testmod.o
> > -CFLAGS_bpf_testmod.o = -I$(src)
> > +CFLAGS_bpf_testmod.o = -I$(src) -O0
> >
> > The build fails due to asm stuff.
> >
> > Maybe we should make scripts/pahole-flags.sh selective
> > and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
> >
> > Thoughts?
> 
> It's even worse with clang compiled kernel:

I tested what is now in the master branch with both gcc and clang, on
fedora:37, Alan also tested it, Jiri, it would be great if you could
check if reverting the revert works for you as well.

Thanks,

- Arnaldo

>     WARN: resolve_btfids: unresolved symbol tcp_reno_cong_avoid
>     WARN: resolve_btfids: unresolved symbol dctcp_update_alpha
>     WARN: resolve_btfids: unresolved symbol cubictcp_cong_avoid
>     WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_timestamp
>     WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_hash
>     WARN: resolve_btfids: unresolved symbol bpf_task_kptr_get
>     WARN: resolve_btfids: unresolved symbol bpf_task_acquire_not_zero
>     WARN: resolve_btfids: unresolved symbol bpf_rdonly_cast
>     WARN: resolve_btfids: unresolved symbol
> bpf_kfunc_call_test_static_unused_arg
>     WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_ref
> 
> so I reverted this commit for now.
> Looks like pahole with skip_encoding_btf_inconsistent_proto needs
> to be more accurate.
> It's way too aggressive removing valid functions.

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Wed, Mar 08, 2023 at 10:53:51PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Feb 13, 2023 at 10:09:21PM -0800, Alexei Starovoitov escreveu:
> > On Mon, Feb 13, 2023 at 7:12 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > > On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> > > > +++ b/scripts/pahole-flags.sh
> > > > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > > >         # see PAHOLE_HAS_LANG_EXCLUDE
> > > >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > > >  fi
> > > > +if [ "${pahole_ver}" -ge "125" ]; then
> > > > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > > > +fi
> > >
> > > We landed this too soon.
> > > #229     tracing_struct:FAIL
> > > is failing now.
> > > since bpf_testmod.ko is missing a bunch of functions though they're global.
> > >
> > > I've tried a bunch of different flags and attributes, but none of them
> > > helped.
> > > The only thing that works is:
> > > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > index 46500636d8cd..5fd0f75d5d20 100644
> > > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
> > >         long b;
> > >  };
> > >
> > > +__attribute__((optimize("-O0")))
> > >  noinline int
> > >  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
> > > b, int c) {
> > >
> > > We cannot do:
> > > --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > > +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > > @@ -10,7 +10,7 @@ endif
> > >  MODULES = bpf_testmod.ko
> > >
> > >  obj-m += bpf_testmod.o
> > > -CFLAGS_bpf_testmod.o = -I$(src)
> > > +CFLAGS_bpf_testmod.o = -I$(src) -O0
> > >
> > > The build fails due to asm stuff.
> > >
> > > Maybe we should make scripts/pahole-flags.sh selective
> > > and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
> > >
> > > Thoughts?
> > 
> > It's even worse with clang compiled kernel:
> 
> I tested what is now in the master branch with both gcc and clang, on
> fedora:37, Alan also tested it, Jiri, it would be great if you could
> check if reverting the revert works for you as well.

ok, will check your master branch

jirka

> 
> Thanks,
> 
> - Arnaldo
> 
> >     WARN: resolve_btfids: unresolved symbol tcp_reno_cong_avoid
> >     WARN: resolve_btfids: unresolved symbol dctcp_update_alpha
> >     WARN: resolve_btfids: unresolved symbol cubictcp_cong_avoid
> >     WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_timestamp
> >     WARN: resolve_btfids: unresolved symbol bpf_xdp_metadata_rx_hash
> >     WARN: resolve_btfids: unresolved symbol bpf_task_kptr_get
> >     WARN: resolve_btfids: unresolved symbol bpf_task_acquire_not_zero
> >     WARN: resolve_btfids: unresolved symbol bpf_rdonly_cast
> >     WARN: resolve_btfids: unresolved symbol
> > bpf_kfunc_call_test_static_unused_arg
> >     WARN: resolve_btfids: unresolved symbol bpf_kfunc_call_test_ref
> > 
> > so I reverted this commit for now.
> > Looks like pahole with skip_encoding_btf_inconsistent_proto needs
> > to be more accurate.
> > It's way too aggressive removing valid functions.

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Thu, Mar 09, 2023 at 09:16:53AM +0100, Jiri Olsa wrote:
> On Wed, Mar 08, 2023 at 10:53:51PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Feb 13, 2023 at 10:09:21PM -0800, Alexei Starovoitov escreveu:
> > > On Mon, Feb 13, 2023 at 7:12 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > > > On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> > > > > +++ b/scripts/pahole-flags.sh
> > > > > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > > > >         # see PAHOLE_HAS_LANG_EXCLUDE
> > > > >         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > > > >  fi
> > > > > +if [ "${pahole_ver}" -ge "125" ]; then
> > > > > +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > > > > +fi
> > > >
> > > > We landed this too soon.
> > > > #229     tracing_struct:FAIL
> > > > is failing now.
> > > > since bpf_testmod.ko is missing a bunch of functions though they're global.
> > > >
> > > > I've tried a bunch of different flags and attributes, but none of them
> > > > helped.
> > > > The only thing that works is:
> > > > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > > b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > > index 46500636d8cd..5fd0f75d5d20 100644
> > > > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > > > @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
> > > >         long b;
> > > >  };
> > > >
> > > > +__attribute__((optimize("-O0")))
> > > >  noinline int
> > > >  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
> > > > b, int c) {
> > > >
> > > > We cannot do:
> > > > --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > > > +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
> > > > @@ -10,7 +10,7 @@ endif
> > > >  MODULES = bpf_testmod.ko
> > > >
> > > >  obj-m += bpf_testmod.o
> > > > -CFLAGS_bpf_testmod.o = -I$(src)
> > > > +CFLAGS_bpf_testmod.o = -I$(src) -O0
> > > >
> > > > The build fails due to asm stuff.
> > > >
> > > > Maybe we should make scripts/pahole-flags.sh selective
> > > > and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
> > > >
> > > > Thoughts?
> > > 
> > > It's even worse with clang compiled kernel:
> > 
> > I tested what is now in the master branch with both gcc and clang, on
> > fedora:37, Alan also tested it, Jiri, it would be great if you could
> > check if reverting the revert works for you as well.
> 
> ok, will check your master branch

looks good.. got no duplicates and passing bpf tests for both
gcc and clang setups

jirka

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Arnaldo Carvalho de Melo]

Em Thu, Mar 09, 2023 at 11:11:27AM +0100, Jiri Olsa escreveu:
> On Thu, Mar 09, 2023 at 09:16:53AM +0100, Jiri Olsa wrote:
> > On Wed, Mar 08, 2023 at 10:53:51PM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Mon, Feb 13, 2023 at 10:09:21PM -0800, Alexei Starovoitov escreveu:
> > > > On Mon, Feb 13, 2023 at 7:12 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> > > > > Maybe we should make scripts/pahole-flags.sh selective
> > > > > and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?

> > > > > Thoughts?

> > > > It's even worse with clang compiled kernel:

> > > I tested what is now in the master branch with both gcc and clang, on
> > > fedora:37, Alan also tested it, Jiri, it would be great if you could
> > > check if reverting the revert works for you as well.

> > ok, will check your master branch

> looks good.. got no duplicates and passing bpf tests for both
> gcc and clang setups

Thanks for testing!

Alexei, since you hit those problems, please consider redoing those
tests in your environment so that we triple check all this.

Thanks,

- Arnaldo

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alan Maguire]

On 09/03/2023 10:11, Jiri Olsa wrote:
> On Thu, Mar 09, 2023 at 09:16:53AM +0100, Jiri Olsa wrote:
>> On Wed, Mar 08, 2023 at 10:53:51PM -0300, Arnaldo Carvalho de Melo wrote:
>>> Em Mon, Feb 13, 2023 at 10:09:21PM -0800, Alexei Starovoitov escreveu:
>>>> On Mon, Feb 13, 2023 at 7:12 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
>>>>> On Thu, Feb 9, 2023 at 5:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>>>>> +++ b/scripts/pahole-flags.sh
>>>>>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>>>>>         # see PAHOLE_HAS_LANG_EXCLUDE
>>>>>>         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>>>>>  fi
>>>>>> +if [ "${pahole_ver}" -ge "125" ]; then
>>>>>> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
>>>>>> +fi
>>>>>
>>>>> We landed this too soon.
>>>>> #229     tracing_struct:FAIL
>>>>> is failing now.
>>>>> since bpf_testmod.ko is missing a bunch of functions though they're global.
>>>>>
>>>>> I've tried a bunch of different flags and attributes, but none of them
>>>>> helped.
>>>>> The only thing that works is:
>>>>> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
>>>>> b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
>>>>> index 46500636d8cd..5fd0f75d5d20 100644
>>>>> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
>>>>> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
>>>>> @@ -28,6 +28,7 @@ struct bpf_testmod_struct_arg_2 {
>>>>>         long b;
>>>>>  };
>>>>>
>>>>> +__attribute__((optimize("-O0")))
>>>>>  noinline int
>>>>>  bpf_testmod_test_struct_arg_1(struct bpf_testmod_struct_arg_2 a, int
>>>>> b, int c) {
>>>>>
>>>>> We cannot do:
>>>>> --- a/tools/testing/selftests/bpf/bpf_testmod/Makefile
>>>>> +++ b/tools/testing/selftests/bpf/bpf_testmod/Makefile
>>>>> @@ -10,7 +10,7 @@ endif
>>>>>  MODULES = bpf_testmod.ko
>>>>>
>>>>>  obj-m += bpf_testmod.o
>>>>> -CFLAGS_bpf_testmod.o = -I$(src)
>>>>> +CFLAGS_bpf_testmod.o = -I$(src) -O0
>>>>>
>>>>> The build fails due to asm stuff.
>>>>>
>>>>> Maybe we should make scripts/pahole-flags.sh selective
>>>>> and don't apply skip_encoding_btf_inconsiste to bpf_testmod ?
>>>>>
>>>>> Thoughts?
>>>>
>>>> It's even worse with clang compiled kernel:
>>>
>>> I tested what is now in the master branch with both gcc and clang, on
>>> fedora:37, Alan also tested it, Jiri, it would be great if you could
>>> check if reverting the revert works for you as well.
>>
>> ok, will check your master branch
> 
> looks good.. got no duplicates and passing bpf tests for both
> gcc and clang setups
>

thanks for re-testing! I just did the same for latest bpf-next
on x86_64/aarch64; all looks good.

Alan

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Yonghong Song]

On 5/15/23 7:53 AM, Alan Maguire wrote:
> On 15/05/2023 05:06, Yonghong Song wrote:
>>
>>
>> On 5/14/23 2:49 PM, Jiri Olsa wrote:
>>> On Sun, May 14, 2023 at 10:37:08AM -0700, Yonghong Song wrote:
>>>>
>>>>
>>>> On 5/12/23 7:59 PM, Yonghong Song wrote:
>>>>>
>>>>>
>>>>> On 5/12/23 2:54 PM, Jiri Olsa wrote:
>>>>>> On Fri, May 12, 2023 at 11:59:34AM -0700, Alexei Starovoitov wrote:
>>>>>>> On Fri, May 12, 2023 at 9:04 AM Alan Maguire
>>>>>>> <alan.maguire@oracle.com> wrote:
>>>>>>>>
>>>>>>>> On 12/05/2023 03:51, Yafang Shao wrote:
>>>>>>>>> On Wed, May 10, 2023 at 9:03 PM Alan Maguire
>>>>>>>>> <alan.maguire@oracle.com> wrote:
>>>>>>>>>>
>>>>>>>>>> v1.25 of pahole supports filtering out functions
>>>>>>>>>> with multiple inconsistent
>>>>>>>>>> function prototypes or optimized-out parameters from
>>>>>>>>>> the BTF representation.
>>>>>>>>>> These present problems because there is no
>>>>>>>>>> additional info in BTF saying which
>>>>>>>>>> inconsistent prototype matches which function
>>>>>>>>>> instance to help guide attachment,
>>>>>>>>>> and functions with optimized-out parameters can lead
>>>>>>>>>> to incorrect assumptions
>>>>>>>>>> about register contents.
>>>>>>>>>>
>>>>>>>>>> So for now, filter out such functions while adding
>>>>>>>>>> BTF representations for
>>>>>>>>>> functions that have "."-suffixes (foo.isra.0) but
>>>>>>>>>> not optimized-out parameters.
>>>>>>>>>> This patch assumes that below linked changes land in
>>>>>>>>>> pahole for v1.25.
>>>>>>>>>>
>>>>>>>>>> Issues with pahole filtering being too aggressive in
>>>>>>>>>> removing functions
>>>>>>>>>> appear to be resolved now, but CI and further testing will
>>>>>>>>>> confirm.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>>>>>>>>>> ---
>>>>>>>>>>     scripts/pahole-flags.sh | 3 +++
>>>>>>>>>>     1 file changed, 3 insertions(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>>>>>>>>>> index 1f1f1d397c39..728d55190d97 100755
>>>>>>>>>> --- a/scripts/pahole-flags.sh
>>>>>>>>>> +++ b/scripts/pahole-flags.sh
>>>>>>>>>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>>>>>>>>>            # see PAHOLE_HAS_LANG_EXCLUDE
>>>>>>>>>>            extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>>>>>>>>>     fi
>>>>>>>>>> +if [ "${pahole_ver}" -ge "125" ]; then
>>>>>>>>>> +       extra_paholeopt="${extra_paholeopt}
>>>>>>>>>> --skip_encoding_btf_inconsistent_proto
>>>>>>>>>> --btf_gen_optimized"
>>>>>>>>>> +fi
>>>>>>>>>>
>>>>>>>>>>     echo ${extra_paholeopt}
>>>>>>>>>> -- 
>>>>>>>>>> 2.31.1
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> That change looks like a workaround to me.
>>>>>>>>> There may be multiple functions that have the same proto, e.g.:
>>>>>>>>>
>>>>>>>>>      $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
>>>>>>>>> kernel/bpf/ net/core/
>>>>>>>>>      kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
>>>>>>>>> bpf_iter_aux_info *aux)
>>>>>>>>>      net/core/bpf_sk_storage.c:static void
>>>>>>>>> bpf_iter_detach_map(struct
>>>>>>>>> bpf_iter_aux_info *aux)
>>>>>>>>>
>>>>>>>>>      $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
>>>>>>>>> bpf_iter_detach_map
>>>>>>>>>      [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
>>>>>>>>>      'aux' type_id=2638
>>>>>>>>>      [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
>>>>>>>>>
>>>>>>>>> We don't know which one it is in the BTF.
>>>>>>>>> However, I'm not against this change, as it can avoid some issues.
>>>>>>>>>
>>>>>>>>
>>>>>>>> In the above case, the BTF representation is consistent though.
>>>>>>>> That is, if I attach fentry progs to either of these functions
>>>>>>>> based on that BTF representation, nothing will crash.
>>>>>>>>
>>>>>>>> That's ultimately what those changes are about; ensuring
>>>>>>>> consistency in BTF representation, so when a function is in
>>>>>>>> BTF we can know the signature of the function can be safely
>>>>>>>> used by fentry for example.
>>>>>>>>
>>>>>>>> The question of being able to identify functions (as opposed
>>>>>>>> to having a consistent representation) is the next step.
>>>>>>>> Finding a way to link between kallsyms and BTF would allow us to
>>>>>>>> have multiple inconsistent functions in BTF, since we could map
>>>>>>>> from BTF -> kallsyms safely. So two functions called "foo"
>>>>>>>> with different function signatures would be okay, because
>>>>>>>> we'd know which was which in kallsyms and could attach
>>>>>>>> safely. Something like a BTF tag for the function that could
>>>>>>>> clarify that mapping - but just for cases where it would
>>>>>>>> otherwise be ambiguous - is probably the way forward
>>>>>>>> longer term.
>>>>>>>>
>>>>>>>> Jiri's talking about this topic at LSF/MM/BPF this week I believe.
>>>>>>>
>>>>>>> Jiri presented a few ideas during LSFMMBPF.
>>>>>>>
>>>>>>> I feel the best approach is to add a set of addr-s to BTF
>>>>>>> via a special decl_tag.
>>>>>>> We can also consider extending KIND_FUNC.
>>>>>>> The advantage that every BTF func will have one or more addrs
>>>>>>> associated with it and bpf prog loading logic wouldn't need to do
>>>>>>> fragile name comparison between btf and kallsyms.
>>>>>>> pahole can take addrs from dwarf and optionally double check
>>>>>>> with kallsyms.
>>>>>>
>>>>>> Yonghong summed it up in another email discussion, pasting it in here:
>>>>>>
>>>>>>      So overall we have three options as kallsyms representation now:
>>>>>>        (a) "addr module:foo:dir_a/dir_b/core.c"
>>>>>>        (b) "addr module:foo"
>>>>>>        (c) "addr module:foo:btf_id"
>>>>>>
>>>>>>      option (a):
>>>>>>        'dir_a/dir_b/core.c' needs to be encoded in BTF.
>>>>>>        user space either check file path or func signature
>>>>>>        to find attach_btf_id and pass to the kernel.
>>>>>>        kernel can find file path in BTF and then lookup
>>>>>>        kallsyms to find addr.
>>>>>>
> 
> I like the source-centric nature of this, but the only
> danger here is we might not get a 1:1 mapping between
> source file location and address; consider the case
> of a static inline function in a .h file which doesn't
> get inlined. It could have multiple addresses associated
> with the same source. For example:
> 
> static inline void __list_del_entry(struct list_head *entry)
> {
> 	if (!__list_del_entry_valid(entry))
> 		return;
> 
> 	__list_del(entry->prev, entry->next);
> }
> 
> $ grep __list_del_entry /proc/kallsyms
> ffffffff982cc5c0 t __pfx___list_del_entry
> ffffffff982cc5d0 t __list_del_entry
> ffffffff985b0860 t __pfx___list_del_entry
> ffffffff985b0870 t __list_del_entry
> ffffffff9862d800 t __pfx___list_del_entry
> ffffffff9862d810 t __list_del_entry
> ffffffff987d3dd0 t __pfx___list_del_entry
> ffffffff987d3de0 t __list_del_entry
> ffffffff987f37a0 T __pfx___list_del_entry_valid
> ffffffff987f37b0 T __list_del_entry_valid
> ffffffff989fdd10 t __pfx___list_del_entry
> ffffffff989fdd20 t __list_del_entry
> ffffffff99baf08c r __ksymtab___list_del_entry_valid
> ffffffffc12da2e0 t __list_del_entry	[bnep]
> ffffffffc12da2d0 t __pfx___list_del_entry	[bnep]
> ffffffffc092d6b0 t __list_del_entry	[videobuf2_common]
> ffffffffc092d6a0 t __pfx___list_del_entry	[videobuf2_common]

Until now, we are okay with static inline function carried
into .o file since all inline functions are marked as notrace
(fentry cannot attach to it.)

However, now we have
https://lore.kernel.org/live-patching/20230502164102.1a51cdb4@gandalf.local.home/T/#u

If the patch is merged, then the above inline function
in the header survived in .o file indeed a problem.

Typically users won't trace inline functions in
the header file. But for completeness, agree that
file path may not fully reliable.

> 
>>>>>>      option (b):
>>>>>>        "addr" needs to be encoded in BTF.
>>>>>>        user space checks func signature to find
>>>>>>        attach_btf_id and pass to the kernel.
>>>>>>        kernel can find addr in BTF and use it.
>>>>>>
> 
> This seems like the safest option to me. Ideally we wouldn't
> need such information for every function - only ones with
> multiple sites and ambiguous signatures - but the problem
> is a function could have the same name in a kernel and
> a module too. So it seems like we're stuck with providing
> additional info to clarify which signature goes with which
> function for each static function.

When passing attach_btf_id to kernel, we have attach_btf_obj_fd
as well, which should differentiate whether it is kernel or which module 
it is.

> 
>>>>>>      option (c):
>>>>>>        if user can decide which function to attach, e.g.,
>>>>>>        through func signature, then no BTF encoding
>>>>>>        is necessary. attach_btf_id is passed to the
>>>>>>        kernel and search kallsyms to find the matching
>>>>>>        btf_id and 'addr' will be available then.
>>>>>>
>>>>>>      For option (b) and (c), user space needs to check
>>>>>>      func signature to find which btf_id to use. If
>>>>>>      same-name static functions having the identical
>>>>>>      signatures, then user space would have a hard time
>>>>>>      to differentiate. I think it should be very
>>>>>>      rare same-name static functions in the kernel will have
>>>>>>      identical signatures. But if we want 100% correctness,
>>>>>>      we may need file path in which case option (a)
>>>>>>      is preferable.
>>>>>
>>>>> As Alexei mentioned in previous email, for such a extreme case,
>>>>> if user is willing to go through extra step to check dwarf
>>>>> to find and match file path, then (b) and (c) should work
>>>>> perfectly as well.
>>>>
>>>> Okay, it looks like this is more complex if the function signature is
>>>> the same. In such cases, current BTF dedup will merge these
>>>> functions as a single BTF func. In such cases, we could have:
>>>>
>>>>      decl_tag_1   ----> dedup'ed static_func
>>>>                            ^
>>>>                            |
>>>>      decl_tag_2   ---------
>>>>
>>>> For such cases, just passing btf_id of static func to kernel
>>>> won't work since the kernel won't be able to know which
>>>> decl_tag to be associated with.
>>>>
>>>> (I did a simple test with vmlinux, it looks we have
>>>>    issues with decl_tag_1/decl_tag_2 -> dedup'ed static_func
>>>>    as well since only one of decl_tag survives.
>>>>    But this is a different issue.
>>>> )
>>>>
>>>> So if we intend to add decl tag (addr or file_path), we
>>>> should not dedup static functions or generally any functions.
>>>
>>> I did not think functions would be dedup-ed, they are ;-) with the
>>> declaration tags in place we could perhaps switch it off, right?
>>
>> That is my hope too. If with decl tag func won't be dedup'ed,
>> then we should be okay. In the kernel, based on attach_btf_id,
>> through btf, kernel can find the corresponding decl tag (file path
>> or addr) or through attach_btf_id itself if the btf id is
>> encoded in kallsym entries.
>>
>>>
>>> or perhaps I can't think of all the cases we need functions dedup for,
>>> so maybe the dedup code could check also the associated decl tag when
>>> comparing functions
>>>
> 
> Would using the BTF decl tag id instead of the function BTF id to
> guide attachment be an option? That way if multiple functions shared
> the same signature, we could still get the info to figure out which to
> attach to from the decl tag, and we wouldn't need to mess with dedup.
> I'm probably missing something which makes that unworkable, but just a
> thought. Thanks!

The issue is due to current bpf syscall UAPI. it passed attach_btf_id
and attach_btf_obj_fd to the kernel. If we change UAPI to pass
decl_tag_id instead of attach_btf_id to the kernel, we should be
okay, but this requires a bpf syscall UAPI change. Maybe this works too.

> 
> Alan

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alan Maguire]

On 15/05/2023 05:06, Yonghong Song wrote:
> 
> 
> On 5/14/23 2:49 PM, Jiri Olsa wrote:
>> On Sun, May 14, 2023 at 10:37:08AM -0700, Yonghong Song wrote:
>>>
>>>
>>> On 5/12/23 7:59 PM, Yonghong Song wrote:
>>>>
>>>>
>>>> On 5/12/23 2:54 PM, Jiri Olsa wrote:
>>>>> On Fri, May 12, 2023 at 11:59:34AM -0700, Alexei Starovoitov wrote:
>>>>>> On Fri, May 12, 2023 at 9:04 AM Alan Maguire
>>>>>> <alan.maguire@oracle.com> wrote:
>>>>>>>
>>>>>>> On 12/05/2023 03:51, Yafang Shao wrote:
>>>>>>>> On Wed, May 10, 2023 at 9:03 PM Alan Maguire
>>>>>>>> <alan.maguire@oracle.com> wrote:
>>>>>>>>>
>>>>>>>>> v1.25 of pahole supports filtering out functions
>>>>>>>>> with multiple inconsistent
>>>>>>>>> function prototypes or optimized-out parameters from
>>>>>>>>> the BTF representation.
>>>>>>>>> These present problems because there is no
>>>>>>>>> additional info in BTF saying which
>>>>>>>>> inconsistent prototype matches which function
>>>>>>>>> instance to help guide attachment,
>>>>>>>>> and functions with optimized-out parameters can lead
>>>>>>>>> to incorrect assumptions
>>>>>>>>> about register contents.
>>>>>>>>>
>>>>>>>>> So for now, filter out such functions while adding
>>>>>>>>> BTF representations for
>>>>>>>>> functions that have "."-suffixes (foo.isra.0) but
>>>>>>>>> not optimized-out parameters.
>>>>>>>>> This patch assumes that below linked changes land in
>>>>>>>>> pahole for v1.25.
>>>>>>>>>
>>>>>>>>> Issues with pahole filtering being too aggressive in
>>>>>>>>> removing functions
>>>>>>>>> appear to be resolved now, but CI and further testing will
>>>>>>>>> confirm.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>>>>>>>>> ---
>>>>>>>>>    scripts/pahole-flags.sh | 3 +++
>>>>>>>>>    1 file changed, 3 insertions(+)
>>>>>>>>>
>>>>>>>>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>>>>>>>>> index 1f1f1d397c39..728d55190d97 100755
>>>>>>>>> --- a/scripts/pahole-flags.sh
>>>>>>>>> +++ b/scripts/pahole-flags.sh
>>>>>>>>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>>>>>>>>           # see PAHOLE_HAS_LANG_EXCLUDE
>>>>>>>>>           extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>>>>>>>>    fi
>>>>>>>>> +if [ "${pahole_ver}" -ge "125" ]; then
>>>>>>>>> +       extra_paholeopt="${extra_paholeopt}
>>>>>>>>> --skip_encoding_btf_inconsistent_proto
>>>>>>>>> --btf_gen_optimized"
>>>>>>>>> +fi
>>>>>>>>>
>>>>>>>>>    echo ${extra_paholeopt}
>>>>>>>>> -- 
>>>>>>>>> 2.31.1
>>>>>>>>>
>>>>>>>>
>>>>>>>> That change looks like a workaround to me.
>>>>>>>> There may be multiple functions that have the same proto, e.g.:
>>>>>>>>
>>>>>>>>     $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
>>>>>>>> kernel/bpf/ net/core/
>>>>>>>>     kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
>>>>>>>> bpf_iter_aux_info *aux)
>>>>>>>>     net/core/bpf_sk_storage.c:static void
>>>>>>>> bpf_iter_detach_map(struct
>>>>>>>> bpf_iter_aux_info *aux)
>>>>>>>>
>>>>>>>>     $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
>>>>>>>> bpf_iter_detach_map
>>>>>>>>     [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
>>>>>>>>     'aux' type_id=2638
>>>>>>>>     [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
>>>>>>>>
>>>>>>>> We don't know which one it is in the BTF.
>>>>>>>> However, I'm not against this change, as it can avoid some issues.
>>>>>>>>
>>>>>>>
>>>>>>> In the above case, the BTF representation is consistent though.
>>>>>>> That is, if I attach fentry progs to either of these functions
>>>>>>> based on that BTF representation, nothing will crash.
>>>>>>>
>>>>>>> That's ultimately what those changes are about; ensuring
>>>>>>> consistency in BTF representation, so when a function is in
>>>>>>> BTF we can know the signature of the function can be safely
>>>>>>> used by fentry for example.
>>>>>>>
>>>>>>> The question of being able to identify functions (as opposed
>>>>>>> to having a consistent representation) is the next step.
>>>>>>> Finding a way to link between kallsyms and BTF would allow us to
>>>>>>> have multiple inconsistent functions in BTF, since we could map
>>>>>>> from BTF -> kallsyms safely. So two functions called "foo"
>>>>>>> with different function signatures would be okay, because
>>>>>>> we'd know which was which in kallsyms and could attach
>>>>>>> safely. Something like a BTF tag for the function that could
>>>>>>> clarify that mapping - but just for cases where it would
>>>>>>> otherwise be ambiguous - is probably the way forward
>>>>>>> longer term.
>>>>>>>
>>>>>>> Jiri's talking about this topic at LSF/MM/BPF this week I believe.
>>>>>>
>>>>>> Jiri presented a few ideas during LSFMMBPF.
>>>>>>
>>>>>> I feel the best approach is to add a set of addr-s to BTF
>>>>>> via a special decl_tag.
>>>>>> We can also consider extending KIND_FUNC.
>>>>>> The advantage that every BTF func will have one or more addrs
>>>>>> associated with it and bpf prog loading logic wouldn't need to do
>>>>>> fragile name comparison between btf and kallsyms.
>>>>>> pahole can take addrs from dwarf and optionally double check
>>>>>> with kallsyms.
>>>>>
>>>>> Yonghong summed it up in another email discussion, pasting it in here:
>>>>>
>>>>>     So overall we have three options as kallsyms representation now:
>>>>>       (a) "addr module:foo:dir_a/dir_b/core.c"
>>>>>       (b) "addr module:foo"
>>>>>       (c) "addr module:foo:btf_id"
>>>>>
>>>>>     option (a):
>>>>>       'dir_a/dir_b/core.c' needs to be encoded in BTF.
>>>>>       user space either check file path or func signature
>>>>>       to find attach_btf_id and pass to the kernel.
>>>>>       kernel can find file path in BTF and then lookup
>>>>>       kallsyms to find addr.
>>>>>

I like the source-centric nature of this, but the only
danger here is we might not get a 1:1 mapping between
source file location and address; consider the case
of a static inline function in a .h file which doesn't
get inlined. It could have multiple addresses associated
with the same source. For example:

static inline void __list_del_entry(struct list_head *entry)
{
	if (!__list_del_entry_valid(entry))
		return;

	__list_del(entry->prev, entry->next);
}

$ grep __list_del_entry /proc/kallsyms
ffffffff982cc5c0 t __pfx___list_del_entry
ffffffff982cc5d0 t __list_del_entry
ffffffff985b0860 t __pfx___list_del_entry
ffffffff985b0870 t __list_del_entry
ffffffff9862d800 t __pfx___list_del_entry
ffffffff9862d810 t __list_del_entry
ffffffff987d3dd0 t __pfx___list_del_entry
ffffffff987d3de0 t __list_del_entry
ffffffff987f37a0 T __pfx___list_del_entry_valid
ffffffff987f37b0 T __list_del_entry_valid
ffffffff989fdd10 t __pfx___list_del_entry
ffffffff989fdd20 t __list_del_entry
ffffffff99baf08c r __ksymtab___list_del_entry_valid
ffffffffc12da2e0 t __list_del_entry	[bnep]
ffffffffc12da2d0 t __pfx___list_del_entry	[bnep]
ffffffffc092d6b0 t __list_del_entry	[videobuf2_common]
ffffffffc092d6a0 t __pfx___list_del_entry	[videobuf2_common]

>>>>>     option (b):
>>>>>       "addr" needs to be encoded in BTF.
>>>>>       user space checks func signature to find
>>>>>       attach_btf_id and pass to the kernel.
>>>>>       kernel can find addr in BTF and use it.
>>>>>

This seems like the safest option to me. Ideally we wouldn't
need such information for every function - only ones with
multiple sites and ambiguous signatures - but the problem
is a function could have the same name in a kernel and
a module too. So it seems like we're stuck with providing
additional info to clarify which signature goes with which
function for each static function.

>>>>>     option (c):
>>>>>       if user can decide which function to attach, e.g.,
>>>>>       through func signature, then no BTF encoding
>>>>>       is necessary. attach_btf_id is passed to the
>>>>>       kernel and search kallsyms to find the matching
>>>>>       btf_id and 'addr' will be available then.
>>>>>
>>>>>     For option (b) and (c), user space needs to check
>>>>>     func signature to find which btf_id to use. If
>>>>>     same-name static functions having the identical
>>>>>     signatures, then user space would have a hard time
>>>>>     to differentiate. I think it should be very
>>>>>     rare same-name static functions in the kernel will have
>>>>>     identical signatures. But if we want 100% correctness,
>>>>>     we may need file path in which case option (a)
>>>>>     is preferable.
>>>>
>>>> As Alexei mentioned in previous email, for such a extreme case,
>>>> if user is willing to go through extra step to check dwarf
>>>> to find and match file path, then (b) and (c) should work
>>>> perfectly as well.
>>>
>>> Okay, it looks like this is more complex if the function signature is
>>> the same. In such cases, current BTF dedup will merge these
>>> functions as a single BTF func. In such cases, we could have:
>>>
>>>     decl_tag_1   ----> dedup'ed static_func
>>>                           ^
>>>                           |
>>>     decl_tag_2   ---------
>>>
>>> For such cases, just passing btf_id of static func to kernel
>>> won't work since the kernel won't be able to know which
>>> decl_tag to be associated with.
>>>
>>> (I did a simple test with vmlinux, it looks we have
>>>   issues with decl_tag_1/decl_tag_2 -> dedup'ed static_func
>>>   as well since only one of decl_tag survives.
>>>   But this is a different issue.
>>> )
>>>
>>> So if we intend to add decl tag (addr or file_path), we
>>> should not dedup static functions or generally any functions.
>>
>> I did not think functions would be dedup-ed, they are ;-) with the
>> declaration tags in place we could perhaps switch it off, right?
> 
> That is my hope too. If with decl tag func won't be dedup'ed,
> then we should be okay. In the kernel, based on attach_btf_id,
> through btf, kernel can find the corresponding decl tag (file path
> or addr) or through attach_btf_id itself if the btf id is
> encoded in kallsym entries.
> 
>>
>> or perhaps I can't think of all the cases we need functions dedup for,
>> so maybe the dedup code could check also the associated decl tag when
>> comparing functions
>>

Would using the BTF decl tag id instead of the function BTF id to
guide attachment be an option? That way if multiple functions shared
the same signature, we could still get the info to figure out which to
attach to from the decl tag, and we wouldn't need to mess with dedup.
I'm probably missing something which makes that unworkable, but just a
thought. Thanks!

Alan

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Yonghong Song]

On 5/14/23 2:49 PM, Jiri Olsa wrote:
> On Sun, May 14, 2023 at 10:37:08AM -0700, Yonghong Song wrote:
>>
>>
>> On 5/12/23 7:59 PM, Yonghong Song wrote:
>>>
>>>
>>> On 5/12/23 2:54 PM, Jiri Olsa wrote:
>>>> On Fri, May 12, 2023 at 11:59:34AM -0700, Alexei Starovoitov wrote:
>>>>> On Fri, May 12, 2023 at 9:04 AM Alan Maguire
>>>>> <alan.maguire@oracle.com> wrote:
>>>>>>
>>>>>> On 12/05/2023 03:51, Yafang Shao wrote:
>>>>>>> On Wed, May 10, 2023 at 9:03 PM Alan Maguire
>>>>>>> <alan.maguire@oracle.com> wrote:
>>>>>>>>
>>>>>>>> v1.25 of pahole supports filtering out functions
>>>>>>>> with multiple inconsistent
>>>>>>>> function prototypes or optimized-out parameters from
>>>>>>>> the BTF representation.
>>>>>>>> These present problems because there is no
>>>>>>>> additional info in BTF saying which
>>>>>>>> inconsistent prototype matches which function
>>>>>>>> instance to help guide attachment,
>>>>>>>> and functions with optimized-out parameters can lead
>>>>>>>> to incorrect assumptions
>>>>>>>> about register contents.
>>>>>>>>
>>>>>>>> So for now, filter out such functions while adding
>>>>>>>> BTF representations for
>>>>>>>> functions that have "."-suffixes (foo.isra.0) but
>>>>>>>> not optimized-out parameters.
>>>>>>>> This patch assumes that below linked changes land in
>>>>>>>> pahole for v1.25.
>>>>>>>>
>>>>>>>> Issues with pahole filtering being too aggressive in
>>>>>>>> removing functions
>>>>>>>> appear to be resolved now, but CI and further testing will confirm.
>>>>>>>>
>>>>>>>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>>>>>>>> ---
>>>>>>>>    scripts/pahole-flags.sh | 3 +++
>>>>>>>>    1 file changed, 3 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>>>>>>>> index 1f1f1d397c39..728d55190d97 100755
>>>>>>>> --- a/scripts/pahole-flags.sh
>>>>>>>> +++ b/scripts/pahole-flags.sh
>>>>>>>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>>>>>>>           # see PAHOLE_HAS_LANG_EXCLUDE
>>>>>>>>           extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>>>>>>>    fi
>>>>>>>> +if [ "${pahole_ver}" -ge "125" ]; then
>>>>>>>> +       extra_paholeopt="${extra_paholeopt}
>>>>>>>> --skip_encoding_btf_inconsistent_proto
>>>>>>>> --btf_gen_optimized"
>>>>>>>> +fi
>>>>>>>>
>>>>>>>>    echo ${extra_paholeopt}
>>>>>>>> -- 
>>>>>>>> 2.31.1
>>>>>>>>
>>>>>>>
>>>>>>> That change looks like a workaround to me.
>>>>>>> There may be multiple functions that have the same proto, e.g.:
>>>>>>>
>>>>>>>     $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
>>>>>>> kernel/bpf/ net/core/
>>>>>>>     kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
>>>>>>> bpf_iter_aux_info *aux)
>>>>>>>     net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
>>>>>>> bpf_iter_aux_info *aux)
>>>>>>>
>>>>>>>     $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
>>>>>>> bpf_iter_detach_map
>>>>>>>     [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
>>>>>>>     'aux' type_id=2638
>>>>>>>     [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
>>>>>>>
>>>>>>> We don't know which one it is in the BTF.
>>>>>>> However, I'm not against this change, as it can avoid some issues.
>>>>>>>
>>>>>>
>>>>>> In the above case, the BTF representation is consistent though.
>>>>>> That is, if I attach fentry progs to either of these functions
>>>>>> based on that BTF representation, nothing will crash.
>>>>>>
>>>>>> That's ultimately what those changes are about; ensuring
>>>>>> consistency in BTF representation, so when a function is in
>>>>>> BTF we can know the signature of the function can be safely
>>>>>> used by fentry for example.
>>>>>>
>>>>>> The question of being able to identify functions (as opposed
>>>>>> to having a consistent representation) is the next step.
>>>>>> Finding a way to link between kallsyms and BTF would allow us to
>>>>>> have multiple inconsistent functions in BTF, since we could map
>>>>>> from BTF -> kallsyms safely. So two functions called "foo"
>>>>>> with different function signatures would be okay, because
>>>>>> we'd know which was which in kallsyms and could attach
>>>>>> safely. Something like a BTF tag for the function that could
>>>>>> clarify that mapping - but just for cases where it would
>>>>>> otherwise be ambiguous - is probably the way forward
>>>>>> longer term.
>>>>>>
>>>>>> Jiri's talking about this topic at LSF/MM/BPF this week I believe.
>>>>>
>>>>> Jiri presented a few ideas during LSFMMBPF.
>>>>>
>>>>> I feel the best approach is to add a set of addr-s to BTF
>>>>> via a special decl_tag.
>>>>> We can also consider extending KIND_FUNC.
>>>>> The advantage that every BTF func will have one or more addrs
>>>>> associated with it and bpf prog loading logic wouldn't need to do
>>>>> fragile name comparison between btf and kallsyms.
>>>>> pahole can take addrs from dwarf and optionally double check
>>>>> with kallsyms.
>>>>
>>>> Yonghong summed it up in another email discussion, pasting it in here:
>>>>
>>>>     So overall we have three options as kallsyms representation now:
>>>>       (a) "addr module:foo:dir_a/dir_b/core.c"
>>>>       (b) "addr module:foo"
>>>>       (c) "addr module:foo:btf_id"
>>>>
>>>>     option (a):
>>>>       'dir_a/dir_b/core.c' needs to be encoded in BTF.
>>>>       user space either check file path or func signature
>>>>       to find attach_btf_id and pass to the kernel.
>>>>       kernel can find file path in BTF and then lookup
>>>>       kallsyms to find addr.
>>>>
>>>>     option (b):
>>>>       "addr" needs to be encoded in BTF.
>>>>       user space checks func signature to find
>>>>       attach_btf_id and pass to the kernel.
>>>>       kernel can find addr in BTF and use it.
>>>>
>>>>     option (c):
>>>>       if user can decide which function to attach, e.g.,
>>>>       through func signature, then no BTF encoding
>>>>       is necessary. attach_btf_id is passed to the
>>>>       kernel and search kallsyms to find the matching
>>>>       btf_id and 'addr' will be available then.
>>>>
>>>>     For option (b) and (c), user space needs to check
>>>>     func signature to find which btf_id to use. If
>>>>     same-name static functions having the identical
>>>>     signatures, then user space would have a hard time
>>>>     to differentiate. I think it should be very
>>>>     rare same-name static functions in the kernel will have
>>>>     identical signatures. But if we want 100% correctness,
>>>>     we may need file path in which case option (a)
>>>>     is preferable.
>>>
>>> As Alexei mentioned in previous email, for such a extreme case,
>>> if user is willing to go through extra step to check dwarf
>>> to find and match file path, then (b) and (c) should work
>>> perfectly as well.
>>
>> Okay, it looks like this is more complex if the function signature is
>> the same. In such cases, current BTF dedup will merge these
>> functions as a single BTF func. In such cases, we could have:
>>
>>     decl_tag_1   ----> dedup'ed static_func
>>                           ^
>>                           |
>>     decl_tag_2   ---------
>>
>> For such cases, just passing btf_id of static func to kernel
>> won't work since the kernel won't be able to know which
>> decl_tag to be associated with.
>>
>> (I did a simple test with vmlinux, it looks we have
>>   issues with decl_tag_1/decl_tag_2 -> dedup'ed static_func
>>   as well since only one of decl_tag survives.
>>   But this is a different issue.
>> )
>>
>> So if we intend to add decl tag (addr or file_path), we
>> should not dedup static functions or generally any functions.
> 
> I did not think functions would be dedup-ed, they are ;-) with the
> declaration tags in place we could perhaps switch it off, right?

That is my hope too. If with decl tag func won't be dedup'ed,
then we should be okay. In the kernel, based on attach_btf_id,
through btf, kernel can find the corresponding decl tag (file path
or addr) or through attach_btf_id itself if the btf id is
encoded in kallsym entries.

> 
> or perhaps I can't think of all the cases we need functions dedup for,
> so maybe the dedup code could check also the associated decl tag when
> comparing functions
> 
> jirka

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Sun, May 14, 2023 at 10:37:08AM -0700, Yonghong Song wrote:
> 
> 
> On 5/12/23 7:59 PM, Yonghong Song wrote:
> > 
> > 
> > On 5/12/23 2:54 PM, Jiri Olsa wrote:
> > > On Fri, May 12, 2023 at 11:59:34AM -0700, Alexei Starovoitov wrote:
> > > > On Fri, May 12, 2023 at 9:04 AM Alan Maguire
> > > > <alan.maguire@oracle.com> wrote:
> > > > > 
> > > > > On 12/05/2023 03:51, Yafang Shao wrote:
> > > > > > On Wed, May 10, 2023 at 9:03 PM Alan Maguire
> > > > > > <alan.maguire@oracle.com> wrote:
> > > > > > > 
> > > > > > > v1.25 of pahole supports filtering out functions
> > > > > > > with multiple inconsistent
> > > > > > > function prototypes or optimized-out parameters from
> > > > > > > the BTF representation.
> > > > > > > These present problems because there is no
> > > > > > > additional info in BTF saying which
> > > > > > > inconsistent prototype matches which function
> > > > > > > instance to help guide attachment,
> > > > > > > and functions with optimized-out parameters can lead
> > > > > > > to incorrect assumptions
> > > > > > > about register contents.
> > > > > > > 
> > > > > > > So for now, filter out such functions while adding
> > > > > > > BTF representations for
> > > > > > > functions that have "."-suffixes (foo.isra.0) but
> > > > > > > not optimized-out parameters.
> > > > > > > This patch assumes that below linked changes land in
> > > > > > > pahole for v1.25.
> > > > > > > 
> > > > > > > Issues with pahole filtering being too aggressive in
> > > > > > > removing functions
> > > > > > > appear to be resolved now, but CI and further testing will confirm.
> > > > > > > 
> > > > > > > Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > > > > > > ---
> > > > > > >   scripts/pahole-flags.sh | 3 +++
> > > > > > >   1 file changed, 3 insertions(+)
> > > > > > > 
> > > > > > > diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > > > > > > index 1f1f1d397c39..728d55190d97 100755
> > > > > > > --- a/scripts/pahole-flags.sh
> > > > > > > +++ b/scripts/pahole-flags.sh
> > > > > > > @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > > > > > >          # see PAHOLE_HAS_LANG_EXCLUDE
> > > > > > >          extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > > > > > >   fi
> > > > > > > +if [ "${pahole_ver}" -ge "125" ]; then
> > > > > > > +       extra_paholeopt="${extra_paholeopt}
> > > > > > > --skip_encoding_btf_inconsistent_proto
> > > > > > > --btf_gen_optimized"
> > > > > > > +fi
> > > > > > > 
> > > > > > >   echo ${extra_paholeopt}
> > > > > > > -- 
> > > > > > > 2.31.1
> > > > > > > 
> > > > > > 
> > > > > > That change looks like a workaround to me.
> > > > > > There may be multiple functions that have the same proto, e.g.:
> > > > > > 
> > > > > >    $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
> > > > > > kernel/bpf/ net/core/
> > > > > >    kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
> > > > > > bpf_iter_aux_info *aux)
> > > > > >    net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
> > > > > > bpf_iter_aux_info *aux)
> > > > > > 
> > > > > >    $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
> > > > > > bpf_iter_detach_map
> > > > > >    [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
> > > > > >    'aux' type_id=2638
> > > > > >    [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
> > > > > > 
> > > > > > We don't know which one it is in the BTF.
> > > > > > However, I'm not against this change, as it can avoid some issues.
> > > > > > 
> > > > > 
> > > > > In the above case, the BTF representation is consistent though.
> > > > > That is, if I attach fentry progs to either of these functions
> > > > > based on that BTF representation, nothing will crash.
> > > > > 
> > > > > That's ultimately what those changes are about; ensuring
> > > > > consistency in BTF representation, so when a function is in
> > > > > BTF we can know the signature of the function can be safely
> > > > > used by fentry for example.
> > > > > 
> > > > > The question of being able to identify functions (as opposed
> > > > > to having a consistent representation) is the next step.
> > > > > Finding a way to link between kallsyms and BTF would allow us to
> > > > > have multiple inconsistent functions in BTF, since we could map
> > > > > from BTF -> kallsyms safely. So two functions called "foo"
> > > > > with different function signatures would be okay, because
> > > > > we'd know which was which in kallsyms and could attach
> > > > > safely. Something like a BTF tag for the function that could
> > > > > clarify that mapping - but just for cases where it would
> > > > > otherwise be ambiguous - is probably the way forward
> > > > > longer term.
> > > > > 
> > > > > Jiri's talking about this topic at LSF/MM/BPF this week I believe.
> > > > 
> > > > Jiri presented a few ideas during LSFMMBPF.
> > > > 
> > > > I feel the best approach is to add a set of addr-s to BTF
> > > > via a special decl_tag.
> > > > We can also consider extending KIND_FUNC.
> > > > The advantage that every BTF func will have one or more addrs
> > > > associated with it and bpf prog loading logic wouldn't need to do
> > > > fragile name comparison between btf and kallsyms.
> > > > pahole can take addrs from dwarf and optionally double check
> > > > with kallsyms.
> > > 
> > > Yonghong summed it up in another email discussion, pasting it in here:
> > > 
> > >    So overall we have three options as kallsyms representation now:
> > >      (a) "addr module:foo:dir_a/dir_b/core.c"
> > >      (b) "addr module:foo"
> > >      (c) "addr module:foo:btf_id"
> > > 
> > >    option (a):
> > >      'dir_a/dir_b/core.c' needs to be encoded in BTF.
> > >      user space either check file path or func signature
> > >      to find attach_btf_id and pass to the kernel.
> > >      kernel can find file path in BTF and then lookup
> > >      kallsyms to find addr.
> > > 
> > >    option (b):
> > >      "addr" needs to be encoded in BTF.
> > >      user space checks func signature to find
> > >      attach_btf_id and pass to the kernel.
> > >      kernel can find addr in BTF and use it.
> > > 
> > >    option (c):
> > >      if user can decide which function to attach, e.g.,
> > >      through func signature, then no BTF encoding
> > >      is necessary. attach_btf_id is passed to the
> > >      kernel and search kallsyms to find the matching
> > >      btf_id and 'addr' will be available then.
> > > 
> > >    For option (b) and (c), user space needs to check
> > >    func signature to find which btf_id to use. If
> > >    same-name static functions having the identical
> > >    signatures, then user space would have a hard time
> > >    to differentiate. I think it should be very
> > >    rare same-name static functions in the kernel will have
> > >    identical signatures. But if we want 100% correctness,
> > >    we may need file path in which case option (a)
> > >    is preferable.
> > 
> > As Alexei mentioned in previous email, for such a extreme case,
> > if user is willing to go through extra step to check dwarf
> > to find and match file path, then (b) and (c) should work
> > perfectly as well.
> 
> Okay, it looks like this is more complex if the function signature is
> the same. In such cases, current BTF dedup will merge these
> functions as a single BTF func. In such cases, we could have:
> 
>    decl_tag_1   ----> dedup'ed static_func
>                          ^
>                          |
>    decl_tag_2   ---------
> 
> For such cases, just passing btf_id of static func to kernel
> won't work since the kernel won't be able to know which
> decl_tag to be associated with.
> 
> (I did a simple test with vmlinux, it looks we have
>  issues with decl_tag_1/decl_tag_2 -> dedup'ed static_func
>  as well since only one of decl_tag survives.
>  But this is a different issue.
> )
> 
> So if we intend to add decl tag (addr or file_path), we
> should not dedup static functions or generally any functions.

I did not think functions would be dedup-ed, they are ;-) with the
declaration tags in place we could perhaps switch it off, right?

or perhaps I can't think of all the cases we need functions dedup for,
so maybe the dedup code could check also the associated decl tag when
comparing functions

jirka

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Yonghong Song]

On 5/12/23 7:59 PM, Yonghong Song wrote:
> 
> 
> On 5/12/23 2:54 PM, Jiri Olsa wrote:
>> On Fri, May 12, 2023 at 11:59:34AM -0700, Alexei Starovoitov wrote:
>>> On Fri, May 12, 2023 at 9:04 AM Alan Maguire 
>>> <alan.maguire@oracle.com> wrote:
>>>>
>>>> On 12/05/2023 03:51, Yafang Shao wrote:
>>>>> On Wed, May 10, 2023 at 9:03 PM Alan Maguire 
>>>>> <alan.maguire@oracle.com> wrote:
>>>>>>
>>>>>> v1.25 of pahole supports filtering out functions with multiple 
>>>>>> inconsistent
>>>>>> function prototypes or optimized-out parameters from the BTF 
>>>>>> representation.
>>>>>> These present problems because there is no additional info in BTF 
>>>>>> saying which
>>>>>> inconsistent prototype matches which function instance to help 
>>>>>> guide attachment,
>>>>>> and functions with optimized-out parameters can lead to incorrect 
>>>>>> assumptions
>>>>>> about register contents.
>>>>>>
>>>>>> So for now, filter out such functions while adding BTF 
>>>>>> representations for
>>>>>> functions that have "."-suffixes (foo.isra.0) but not 
>>>>>> optimized-out parameters.
>>>>>> This patch assumes that below linked changes land in pahole for 
>>>>>> v1.25.
>>>>>>
>>>>>> Issues with pahole filtering being too aggressive in removing 
>>>>>> functions
>>>>>> appear to be resolved now, but CI and further testing will confirm.
>>>>>>
>>>>>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>>>>>> ---
>>>>>>   scripts/pahole-flags.sh | 3 +++
>>>>>>   1 file changed, 3 insertions(+)
>>>>>>
>>>>>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>>>>>> index 1f1f1d397c39..728d55190d97 100755
>>>>>> --- a/scripts/pahole-flags.sh
>>>>>> +++ b/scripts/pahole-flags.sh
>>>>>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>>>>>          # see PAHOLE_HAS_LANG_EXCLUDE
>>>>>>          extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>>>>>   fi
>>>>>> +if [ "${pahole_ver}" -ge "125" ]; then
>>>>>> +       extra_paholeopt="${extra_paholeopt} 
>>>>>> --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
>>>>>> +fi
>>>>>>
>>>>>>   echo ${extra_paholeopt}
>>>>>> -- 
>>>>>> 2.31.1
>>>>>>
>>>>>
>>>>> That change looks like a workaround to me.
>>>>> There may be multiple functions that have the same proto, e.g.:
>>>>>
>>>>>    $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
>>>>> kernel/bpf/ net/core/
>>>>>    kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
>>>>> bpf_iter_aux_info *aux)
>>>>>    net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
>>>>> bpf_iter_aux_info *aux)
>>>>>
>>>>>    $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
>>>>> bpf_iter_detach_map
>>>>>    [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
>>>>>    'aux' type_id=2638
>>>>>    [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
>>>>>
>>>>> We don't know which one it is in the BTF.
>>>>> However, I'm not against this change, as it can avoid some issues.
>>>>>
>>>>
>>>> In the above case, the BTF representation is consistent though.
>>>> That is, if I attach fentry progs to either of these functions
>>>> based on that BTF representation, nothing will crash.
>>>>
>>>> That's ultimately what those changes are about; ensuring
>>>> consistency in BTF representation, so when a function is in
>>>> BTF we can know the signature of the function can be safely
>>>> used by fentry for example.
>>>>
>>>> The question of being able to identify functions (as opposed
>>>> to having a consistent representation) is the next step.
>>>> Finding a way to link between kallsyms and BTF would allow us to
>>>> have multiple inconsistent functions in BTF, since we could map
>>>> from BTF -> kallsyms safely. So two functions called "foo"
>>>> with different function signatures would be okay, because
>>>> we'd know which was which in kallsyms and could attach
>>>> safely. Something like a BTF tag for the function that could
>>>> clarify that mapping - but just for cases where it would
>>>> otherwise be ambiguous - is probably the way forward
>>>> longer term.
>>>>
>>>> Jiri's talking about this topic at LSF/MM/BPF this week I believe.
>>>
>>> Jiri presented a few ideas during LSFMMBPF.
>>>
>>> I feel the best approach is to add a set of addr-s to BTF
>>> via a special decl_tag.
>>> We can also consider extending KIND_FUNC.
>>> The advantage that every BTF func will have one or more addrs
>>> associated with it and bpf prog loading logic wouldn't need to do
>>> fragile name comparison between btf and kallsyms.
>>> pahole can take addrs from dwarf and optionally double check with 
>>> kallsyms.
>>
>> Yonghong summed it up in another email discussion, pasting it in here:
>>
>>    So overall we have three options as kallsyms representation now:
>>      (a) "addr module:foo:dir_a/dir_b/core.c"
>>      (b) "addr module:foo"
>>      (c) "addr module:foo:btf_id"
>>
>>    option (a):
>>      'dir_a/dir_b/core.c' needs to be encoded in BTF.
>>      user space either check file path or func signature
>>      to find attach_btf_id and pass to the kernel.
>>      kernel can find file path in BTF and then lookup
>>      kallsyms to find addr.
>>
>>    option (b):
>>      "addr" needs to be encoded in BTF.
>>      user space checks func signature to find
>>      attach_btf_id and pass to the kernel.
>>      kernel can find addr in BTF and use it.
>>
>>    option (c):
>>      if user can decide which function to attach, e.g.,
>>      through func signature, then no BTF encoding
>>      is necessary. attach_btf_id is passed to the
>>      kernel and search kallsyms to find the matching
>>      btf_id and 'addr' will be available then.
>>
>>    For option (b) and (c), user space needs to check
>>    func signature to find which btf_id to use. If
>>    same-name static functions having the identical
>>    signatures, then user space would have a hard time
>>    to differentiate. I think it should be very
>>    rare same-name static functions in the kernel will have
>>    identical signatures. But if we want 100% correctness,
>>    we may need file path in which case option (a)
>>    is preferable.
> 
> As Alexei mentioned in previous email, for such a extreme case,
> if user is willing to go through extra step to check dwarf
> to find and match file path, then (b) and (c) should work
> perfectly as well.

Okay, it looks like this is more complex if the function signature is
the same. In such cases, current BTF dedup will merge these
functions as a single BTF func. In such cases, we could have:

    decl_tag_1   ----> dedup'ed static_func
                          ^
                          |
    decl_tag_2   ---------

For such cases, just passing btf_id of static func to kernel
won't work since the kernel won't be able to know which
decl_tag to be associated with.

(I did a simple test with vmlinux, it looks we have
  issues with decl_tag_1/decl_tag_2 -> dedup'ed static_func
  as well since only one of decl_tag survives.
  But this is a different issue.
)

So if we intend to add decl tag (addr or file_path), we
should not dedup static functions or generally any functions.

> 
>>
>>    Current option (a) kallsyms format is under review.
>>    option (c) also needs kallsyms change...
>>
>>
>> my thoughts so far is that I like the idea of storing functions address
>> in BTF (option b), because it's the easiest way
>>
>> on the other hand, user would need debug info to find address for the 
>> function
>> to trace.. but still just for small subset of functions that share 
>> same name
>>
>> also I like Lorenz's idea of storing BTF ID in kalsyms and verifier being
>> able to lookup address based on BTF ID.. seems like easier kallsyms 
>> change,
>> but it would still require storing objects paths in BTF to pick up the
>> correct one
>>
>> cc-ing other folks
>>
>> jirka

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Yonghong Song]

On 5/12/23 2:54 PM, Jiri Olsa wrote:
> On Fri, May 12, 2023 at 11:59:34AM -0700, Alexei Starovoitov wrote:
>> On Fri, May 12, 2023 at 9:04 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>>
>>> On 12/05/2023 03:51, Yafang Shao wrote:
>>>> On Wed, May 10, 2023 at 9:03 PM Alan Maguire <alan.maguire@oracle.com> wrote:
>>>>>
>>>>> v1.25 of pahole supports filtering out functions with multiple inconsistent
>>>>> function prototypes or optimized-out parameters from the BTF representation.
>>>>> These present problems because there is no additional info in BTF saying which
>>>>> inconsistent prototype matches which function instance to help guide attachment,
>>>>> and functions with optimized-out parameters can lead to incorrect assumptions
>>>>> about register contents.
>>>>>
>>>>> So for now, filter out such functions while adding BTF representations for
>>>>> functions that have "."-suffixes (foo.isra.0) but not optimized-out parameters.
>>>>> This patch assumes that below linked changes land in pahole for v1.25.
>>>>>
>>>>> Issues with pahole filtering being too aggressive in removing functions
>>>>> appear to be resolved now, but CI and further testing will confirm.
>>>>>
>>>>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>>>>> ---
>>>>>   scripts/pahole-flags.sh | 3 +++
>>>>>   1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>>>>> index 1f1f1d397c39..728d55190d97 100755
>>>>> --- a/scripts/pahole-flags.sh
>>>>> +++ b/scripts/pahole-flags.sh
>>>>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>>>>          # see PAHOLE_HAS_LANG_EXCLUDE
>>>>>          extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>>>>   fi
>>>>> +if [ "${pahole_ver}" -ge "125" ]; then
>>>>> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
>>>>> +fi
>>>>>
>>>>>   echo ${extra_paholeopt}
>>>>> --
>>>>> 2.31.1
>>>>>
>>>>
>>>> That change looks like a workaround to me.
>>>> There may be multiple functions that have the same proto, e.g.:
>>>>
>>>>    $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
>>>> kernel/bpf/ net/core/
>>>>    kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
>>>> bpf_iter_aux_info *aux)
>>>>    net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
>>>> bpf_iter_aux_info *aux)
>>>>
>>>>    $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
>>>> bpf_iter_detach_map
>>>>    [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
>>>>    'aux' type_id=2638
>>>>    [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
>>>>
>>>> We don't know which one it is in the BTF.
>>>> However, I'm not against this change, as it can avoid some issues.
>>>>
>>>
>>> In the above case, the BTF representation is consistent though.
>>> That is, if I attach fentry progs to either of these functions
>>> based on that BTF representation, nothing will crash.
>>>
>>> That's ultimately what those changes are about; ensuring
>>> consistency in BTF representation, so when a function is in
>>> BTF we can know the signature of the function can be safely
>>> used by fentry for example.
>>>
>>> The question of being able to identify functions (as opposed
>>> to having a consistent representation) is the next step.
>>> Finding a way to link between kallsyms and BTF would allow us to
>>> have multiple inconsistent functions in BTF, since we could map
>>> from BTF -> kallsyms safely. So two functions called "foo"
>>> with different function signatures would be okay, because
>>> we'd know which was which in kallsyms and could attach
>>> safely. Something like a BTF tag for the function that could
>>> clarify that mapping - but just for cases where it would
>>> otherwise be ambiguous - is probably the way forward
>>> longer term.
>>>
>>> Jiri's talking about this topic at LSF/MM/BPF this week I believe.
>>
>> Jiri presented a few ideas during LSFMMBPF.
>>
>> I feel the best approach is to add a set of addr-s to BTF
>> via a special decl_tag.
>> We can also consider extending KIND_FUNC.
>> The advantage that every BTF func will have one or more addrs
>> associated with it and bpf prog loading logic wouldn't need to do
>> fragile name comparison between btf and kallsyms.
>> pahole can take addrs from dwarf and optionally double check with kallsyms.
> 
> Yonghong summed it up in another email discussion, pasting it in here:
> 
>    So overall we have three options as kallsyms representation now:
>      (a) "addr module:foo:dir_a/dir_b/core.c"
>      (b) "addr module:foo"
>      (c) "addr module:foo:btf_id"
> 
>    option (a):
>      'dir_a/dir_b/core.c' needs to be encoded in BTF.
>      user space either check file path or func signature
>      to find attach_btf_id and pass to the kernel.
>      kernel can find file path in BTF and then lookup
>      kallsyms to find addr.
> 
>    option (b):
>      "addr" needs to be encoded in BTF.
>      user space checks func signature to find
>      attach_btf_id and pass to the kernel.
>      kernel can find addr in BTF and use it.
> 
>    option (c):
>      if user can decide which function to attach, e.g.,
>      through func signature, then no BTF encoding
>      is necessary. attach_btf_id is passed to the
>      kernel and search kallsyms to find the matching
>      btf_id and 'addr' will be available then.
> 
>    For option (b) and (c), user space needs to check
>    func signature to find which btf_id to use. If
>    same-name static functions having the identical
>    signatures, then user space would have a hard time
>    to differentiate. I think it should be very
>    rare same-name static functions in the kernel will have
>    identical signatures. But if we want 100% correctness,
>    we may need file path in which case option (a)
>    is preferable.

As Alexei mentioned in previous email, for such a extreme case,
if user is willing to go through extra step to check dwarf
to find and match file path, then (b) and (c) should work
perfectly as well.

> 
>    Current option (a) kallsyms format is under review.
>    option (c) also needs kallsyms change...
> 
> 
> my thoughts so far is that I like the idea of storing functions address
> in BTF (option b), because it's the easiest way
> 
> on the other hand, user would need debug info to find address for the function
> to trace.. but still just for small subset of functions that share same name
> 
> also I like Lorenz's idea of storing BTF ID in kalsyms and verifier being
> able to lookup address based on BTF ID.. seems like easier kallsyms change,
> but it would still require storing objects paths in BTF to pick up the
> correct one
> 
> cc-ing other folks
> 
> jirka

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Fri, May 12, 2023 at 11:59:34AM -0700, Alexei Starovoitov wrote:
> On Fri, May 12, 2023 at 9:04 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> >
> > On 12/05/2023 03:51, Yafang Shao wrote:
> > > On Wed, May 10, 2023 at 9:03 PM Alan Maguire <alan.maguire@oracle.com> wrote:
> > >>
> > >> v1.25 of pahole supports filtering out functions with multiple inconsistent
> > >> function prototypes or optimized-out parameters from the BTF representation.
> > >> These present problems because there is no additional info in BTF saying which
> > >> inconsistent prototype matches which function instance to help guide attachment,
> > >> and functions with optimized-out parameters can lead to incorrect assumptions
> > >> about register contents.
> > >>
> > >> So for now, filter out such functions while adding BTF representations for
> > >> functions that have "."-suffixes (foo.isra.0) but not optimized-out parameters.
> > >> This patch assumes that below linked changes land in pahole for v1.25.
> > >>
> > >> Issues with pahole filtering being too aggressive in removing functions
> > >> appear to be resolved now, but CI and further testing will confirm.
> > >>
> > >> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> > >> ---
> > >>  scripts/pahole-flags.sh | 3 +++
> > >>  1 file changed, 3 insertions(+)
> > >>
> > >> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> > >> index 1f1f1d397c39..728d55190d97 100755
> > >> --- a/scripts/pahole-flags.sh
> > >> +++ b/scripts/pahole-flags.sh
> > >> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> > >>         # see PAHOLE_HAS_LANG_EXCLUDE
> > >>         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> > >>  fi
> > >> +if [ "${pahole_ver}" -ge "125" ]; then
> > >> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> > >> +fi
> > >>
> > >>  echo ${extra_paholeopt}
> > >> --
> > >> 2.31.1
> > >>
> > >
> > > That change looks like a workaround to me.
> > > There may be multiple functions that have the same proto, e.g.:
> > >
> > >   $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
> > > kernel/bpf/ net/core/
> > >   kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
> > > bpf_iter_aux_info *aux)
> > >   net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
> > > bpf_iter_aux_info *aux)
> > >
> > >   $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
> > > bpf_iter_detach_map
> > >   [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
> > >   'aux' type_id=2638
> > >   [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
> > >
> > > We don't know which one it is in the BTF.
> > > However, I'm not against this change, as it can avoid some issues.
> > >
> >
> > In the above case, the BTF representation is consistent though.
> > That is, if I attach fentry progs to either of these functions
> > based on that BTF representation, nothing will crash.
> >
> > That's ultimately what those changes are about; ensuring
> > consistency in BTF representation, so when a function is in
> > BTF we can know the signature of the function can be safely
> > used by fentry for example.
> >
> > The question of being able to identify functions (as opposed
> > to having a consistent representation) is the next step.
> > Finding a way to link between kallsyms and BTF would allow us to
> > have multiple inconsistent functions in BTF, since we could map
> > from BTF -> kallsyms safely. So two functions called "foo"
> > with different function signatures would be okay, because
> > we'd know which was which in kallsyms and could attach
> > safely. Something like a BTF tag for the function that could
> > clarify that mapping - but just for cases where it would
> > otherwise be ambiguous - is probably the way forward
> > longer term.
> >
> > Jiri's talking about this topic at LSF/MM/BPF this week I believe.
> 
> Jiri presented a few ideas during LSFMMBPF.
> 
> I feel the best approach is to add a set of addr-s to BTF
> via a special decl_tag.
> We can also consider extending KIND_FUNC.
> The advantage that every BTF func will have one or more addrs
> associated with it and bpf prog loading logic wouldn't need to do
> fragile name comparison between btf and kallsyms.
> pahole can take addrs from dwarf and optionally double check with kallsyms.

Yonghong summed it up in another email discussion, pasting it in here:

  So overall we have three options as kallsyms representation now:
    (a) "addr module:foo:dir_a/dir_b/core.c"
    (b) "addr module:foo"
    (c) "addr module:foo:btf_id"

  option (a):
    'dir_a/dir_b/core.c' needs to be encoded in BTF.
    user space either check file path or func signature
    to find attach_btf_id and pass to the kernel.
    kernel can find file path in BTF and then lookup
    kallsyms to find addr.

  option (b):
    "addr" needs to be encoded in BTF.
    user space checks func signature to find
    attach_btf_id and pass to the kernel.
    kernel can find addr in BTF and use it.

  option (c):
    if user can decide which function to attach, e.g.,
    through func signature, then no BTF encoding
    is necessary. attach_btf_id is passed to the
    kernel and search kallsyms to find the matching
    btf_id and 'addr' will be available then.

  For option (b) and (c), user space needs to check
  func signature to find which btf_id to use. If
  same-name static functions having the identical
  signatures, then user space would have a hard time
  to differentiate. I think it should be very
  rare same-name static functions in the kernel will have
  identical signatures. But if we want 100% correctness,
  we may need file path in which case option (a)
  is preferable.

  Current option (a) kallsyms format is under review.
  option (c) also needs kallsyms change...


my thoughts so far is that I like the idea of storing functions address
in BTF (option b), because it's the easiest way

on the other hand, user would need debug info to find address for the function
to trace.. but still just for small subset of functions that share same name

also I like Lorenz's idea of storing BTF ID in kalsyms and verifier being
able to lookup address based on BTF ID.. seems like easier kallsyms change,
but it would still require storing objects paths in BTF to pick up the
correct one

cc-ing other folks

jirka

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Wed, 10 May 2023 14:02:41 +0100 you wrote:
> v1.25 of pahole supports filtering out functions with multiple inconsistent
> function prototypes or optimized-out parameters from the BTF representation.
> These present problems because there is no additional info in BTF saying which
> inconsistent prototype matches which function instance to help guide attachment,
> and functions with optimized-out parameters can lead to incorrect assumptions
> about register contents.
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25
    https://git.kernel.org/bpf/bpf-next/c/7b99f75942da

You are awesome, thank you!
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Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alexei Starovoitov]

On Fri, May 12, 2023 at 9:04 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> On 12/05/2023 03:51, Yafang Shao wrote:
> > On Wed, May 10, 2023 at 9:03 PM Alan Maguire <alan.maguire@oracle.com> wrote:
> >>
> >> v1.25 of pahole supports filtering out functions with multiple inconsistent
> >> function prototypes or optimized-out parameters from the BTF representation.
> >> These present problems because there is no additional info in BTF saying which
> >> inconsistent prototype matches which function instance to help guide attachment,
> >> and functions with optimized-out parameters can lead to incorrect assumptions
> >> about register contents.
> >>
> >> So for now, filter out such functions while adding BTF representations for
> >> functions that have "."-suffixes (foo.isra.0) but not optimized-out parameters.
> >> This patch assumes that below linked changes land in pahole for v1.25.
> >>
> >> Issues with pahole filtering being too aggressive in removing functions
> >> appear to be resolved now, but CI and further testing will confirm.
> >>
> >> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> >> ---
> >>  scripts/pahole-flags.sh | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> >> index 1f1f1d397c39..728d55190d97 100755
> >> --- a/scripts/pahole-flags.sh
> >> +++ b/scripts/pahole-flags.sh
> >> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
> >>         # see PAHOLE_HAS_LANG_EXCLUDE
> >>         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
> >>  fi
> >> +if [ "${pahole_ver}" -ge "125" ]; then
> >> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> >> +fi
> >>
> >>  echo ${extra_paholeopt}
> >> --
> >> 2.31.1
> >>
> >
> > That change looks like a workaround to me.
> > There may be multiple functions that have the same proto, e.g.:
> >
> >   $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
> > kernel/bpf/ net/core/
> >   kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
> > bpf_iter_aux_info *aux)
> >   net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
> > bpf_iter_aux_info *aux)
> >
> >   $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
> > bpf_iter_detach_map
> >   [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
> >   'aux' type_id=2638
> >   [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
> >
> > We don't know which one it is in the BTF.
> > However, I'm not against this change, as it can avoid some issues.
> >
>
> In the above case, the BTF representation is consistent though.
> That is, if I attach fentry progs to either of these functions
> based on that BTF representation, nothing will crash.
>
> That's ultimately what those changes are about; ensuring
> consistency in BTF representation, so when a function is in
> BTF we can know the signature of the function can be safely
> used by fentry for example.
>
> The question of being able to identify functions (as opposed
> to having a consistent representation) is the next step.
> Finding a way to link between kallsyms and BTF would allow us to
> have multiple inconsistent functions in BTF, since we could map
> from BTF -> kallsyms safely. So two functions called "foo"
> with different function signatures would be okay, because
> we'd know which was which in kallsyms and could attach
> safely. Something like a BTF tag for the function that could
> clarify that mapping - but just for cases where it would
> otherwise be ambiguous - is probably the way forward
> longer term.
>
> Jiri's talking about this topic at LSF/MM/BPF this week I believe.

Jiri presented a few ideas during LSFMMBPF.

I feel the best approach is to add a set of addr-s to BTF
via a special decl_tag.
We can also consider extending KIND_FUNC.
The advantage that every BTF func will have one or more addrs
associated with it and bpf prog loading logic wouldn't need to do
fragile name comparison between btf and kallsyms.
pahole can take addrs from dwarf and optionally double check with kallsyms.

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alan Maguire]

On 12/05/2023 03:51, Yafang Shao wrote:
> On Wed, May 10, 2023 at 9:03 PM Alan Maguire <alan.maguire@oracle.com> wrote:
>>
>> v1.25 of pahole supports filtering out functions with multiple inconsistent
>> function prototypes or optimized-out parameters from the BTF representation.
>> These present problems because there is no additional info in BTF saying which
>> inconsistent prototype matches which function instance to help guide attachment,
>> and functions with optimized-out parameters can lead to incorrect assumptions
>> about register contents.
>>
>> So for now, filter out such functions while adding BTF representations for
>> functions that have "."-suffixes (foo.isra.0) but not optimized-out parameters.
>> This patch assumes that below linked changes land in pahole for v1.25.
>>
>> Issues with pahole filtering being too aggressive in removing functions
>> appear to be resolved now, but CI and further testing will confirm.
>>
>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>> ---
>>  scripts/pahole-flags.sh | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
>> index 1f1f1d397c39..728d55190d97 100755
>> --- a/scripts/pahole-flags.sh
>> +++ b/scripts/pahole-flags.sh
>> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>>         # see PAHOLE_HAS_LANG_EXCLUDE
>>         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>>  fi
>> +if [ "${pahole_ver}" -ge "125" ]; then
>> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
>> +fi
>>
>>  echo ${extra_paholeopt}
>> --
>> 2.31.1
>>
> 
> That change looks like a workaround to me.
> There may be multiple functions that have the same proto, e.g.:
> 
>   $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
> kernel/bpf/ net/core/
>   kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
> bpf_iter_aux_info *aux)
>   net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
> bpf_iter_aux_info *aux)
> 
>   $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
> bpf_iter_detach_map
>   [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
>   'aux' type_id=2638
>   [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static
> 
> We don't know which one it is in the BTF.
> However, I'm not against this change, as it can avoid some issues.
> 

In the above case, the BTF representation is consistent though.
That is, if I attach fentry progs to either of these functions
based on that BTF representation, nothing will crash.

That's ultimately what those changes are about; ensuring
consistency in BTF representation, so when a function is in
BTF we can know the signature of the function can be safely
used by fentry for example.

The question of being able to identify functions (as opposed
to having a consistent representation) is the next step.
Finding a way to link between kallsyms and BTF would allow us to
have multiple inconsistent functions in BTF, since we could map
from BTF -> kallsyms safely. So two functions called "foo"
with different function signatures would be okay, because
we'd know which was which in kallsyms and could attach
safely. Something like a BTF tag for the function that could
clarify that mapping - but just for cases where it would
otherwise be ambiguous - is probably the way forward
longer term.

Jiri's talking about this topic at LSF/MM/BPF this week I believe.

Thanks!

Alan

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Yafang Shao]

On Wed, May 10, 2023 at 9:03 PM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> v1.25 of pahole supports filtering out functions with multiple inconsistent
> function prototypes or optimized-out parameters from the BTF representation.
> These present problems because there is no additional info in BTF saying which
> inconsistent prototype matches which function instance to help guide attachment,
> and functions with optimized-out parameters can lead to incorrect assumptions
> about register contents.
>
> So for now, filter out such functions while adding BTF representations for
> functions that have "."-suffixes (foo.isra.0) but not optimized-out parameters.
> This patch assumes that below linked changes land in pahole for v1.25.
>
> Issues with pahole filtering being too aggressive in removing functions
> appear to be resolved now, but CI and further testing will confirm.
>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  scripts/pahole-flags.sh | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> index 1f1f1d397c39..728d55190d97 100755
> --- a/scripts/pahole-flags.sh
> +++ b/scripts/pahole-flags.sh
> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>         # see PAHOLE_HAS_LANG_EXCLUDE
>         extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>  fi
> +if [ "${pahole_ver}" -ge "125" ]; then
> +       extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> +fi
>
>  echo ${extra_paholeopt}
> --
> 2.31.1
>

That change looks like a workaround to me.
There may be multiple functions that have the same proto, e.g.:

  $ grep -r "bpf_iter_detach_map(struct bpf_iter_aux_info \*aux)"
kernel/bpf/ net/core/
  kernel/bpf/map_iter.c:static void bpf_iter_detach_map(struct
bpf_iter_aux_info *aux)
  net/core/bpf_sk_storage.c:static void bpf_iter_detach_map(struct
bpf_iter_aux_info *aux)

  $ bpftool btf dump file /sys/kernel/btf/vmlinux   |  grep -B 2
bpf_iter_detach_map
  [34691] FUNC_PROTO '(anon)' ret_type_id=0 vlen=1
  'aux' type_id=2638
  [34692] FUNC 'bpf_iter_detach_map' type_id=34691 linkage=static

We don't know which one it is in the BTF.
However, I'm not against this change, as it can avoid some issues.

-- 
Regards
Yafang

Re: [PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Jiri Olsa]

On Wed, May 10, 2023 at 02:02:41PM +0100, Alan Maguire wrote:
> v1.25 of pahole supports filtering out functions with multiple inconsistent
> function prototypes or optimized-out parameters from the BTF representation.
> These present problems because there is no additional info in BTF saying which
> inconsistent prototype matches which function instance to help guide attachment,
> and functions with optimized-out parameters can lead to incorrect assumptions
> about register contents.
> 
> So for now, filter out such functions while adding BTF representations for
> functions that have "."-suffixes (foo.isra.0) but not optimized-out parameters.
> This patch assumes that below linked changes land in pahole for v1.25.
> 
> Issues with pahole filtering being too aggressive in removing functions
> appear to be resolved now, but CI and further testing will confirm.
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  scripts/pahole-flags.sh | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> index 1f1f1d397c39..728d55190d97 100755
> --- a/scripts/pahole-flags.sh
> +++ b/scripts/pahole-flags.sh
> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>  	# see PAHOLE_HAS_LANG_EXCLUDE
>  	extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>  fi
> +if [ "${pahole_ver}" -ge "125" ]; then
> +	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> +fi
>  
>  echo ${extra_paholeopt}
> -- 
> 2.31.1
> 

[PATCH bpf-next] bpf: Add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Alan Maguire]

v1.25 of pahole supports filtering out functions with multiple inconsistent
function prototypes or optimized-out parameters from the BTF representation.
These present problems because there is no additional info in BTF saying which
inconsistent prototype matches which function instance to help guide attachment,
and functions with optimized-out parameters can lead to incorrect assumptions
about register contents.

So for now, filter out such functions while adding BTF representations for
functions that have "."-suffixes (foo.isra.0) but not optimized-out parameters.
This patch assumes that below linked changes land in pahole for v1.25.

Issues with pahole filtering being too aggressive in removing functions
appear to be resolved now, but CI and further testing will confirm.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 scripts/pahole-flags.sh | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
index 1f1f1d397c39..728d55190d97 100755
--- a/scripts/pahole-flags.sh
+++ b/scripts/pahole-flags.sh
@@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
 	# see PAHOLE_HAS_LANG_EXCLUDE
 	extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
 fi
+if [ "${pahole_ver}" -ge "125" ]; then
+	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
+fi
 
 echo ${extra_paholeopt}
-- 
2.31.1

Re: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto, --btf_gen_optimized to pahole flags for v1.25

[Arnaldo Carvalho de Melo]

Em Wed, Feb 08, 2023 at 05:17:02PM +0000, Alan Maguire escreveu:
> From: Alan Maguire <alan.maguire@oracle.com>
> Date: Thu, 2 Feb 2023 12:26:20 +0000
> Subject: [PATCH bpf-next] bpf: add --skip_encoding_btf_inconsistent_proto,
>  --btf_gen_optimized to pahole flags for v1.25
> 
> v1.25 of pahole supports filtering out functions with multiple
> inconsistent function prototypes or optimized-out parameters
> from the BTF representation.  These present problems because
> there is no additional info in BTF saying which inconsistent
> prototype matches which function instance to help guide
> attachment, and functions with optimized-out parameters can
> lead to incorrect assumptions about register contents.
> 
> So for now, filter out such functions while adding BTF
> representations for functions that have "."-suffixes
> (foo.isra.0) but not optimized-out parameters.
> 
> This patch assumes changes in [1] land and pahole is bumped
> to v1.25.
> 
> [1] https://lore.kernel.org/bpf/1675790102-23037-1-git-send-email-alan.maguire@oracle.com/
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  scripts/pahole-flags.sh | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/scripts/pahole-flags.sh b/scripts/pahole-flags.sh
> index 1f1f1d3..728d551 100755
> --- a/scripts/pahole-flags.sh
> +++ b/scripts/pahole-flags.sh
> @@ -23,5 +23,8 @@ if [ "${pahole_ver}" -ge "124" ]; then
>  	# see PAHOLE_HAS_LANG_EXCLUDE
>  	extra_paholeopt="${extra_paholeopt} --lang_exclude=rust"
>  fi
> +if [ "${pahole_ver}" -ge "125" ]; then
> +	extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
> +fi
>  
>  echo ${extra_paholeopt}
> -- 
> 1.8.3.1


I applied the patch and it works as advertised using what is in pahole's
'next' branch, that should go to 'master' later today.

Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

- Arnaldo