* [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm
@ 2020-10-03 2:19 Yonghong Song
2020-10-03 2:19 ` [PATCH bpf-next 2/2] samples/bpf: fix a compilation error with fallthrough marking Yonghong Song
2020-10-03 4:22 ` [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm Andrii Nakryiko
0 siblings, 2 replies; 6+ messages in thread
From: Yonghong Song @ 2020-10-03 2:19 UTC (permalink / raw)
To: bpf, netdev; +Cc: Alexei Starovoitov, Daniel Borkmann, kernel-team
With latest llvm trunk, bpf programs under samples/bpf
directory, if using CORE, may experience the following
errors:
LLVM ERROR: Cannot select: intrinsic %llvm.preserve.struct.access.index
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
Stack dump:
0. Program arguments: llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
1. Running pass 'Function Pass Manager' on module '<stdin>'.
2. Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@bpf_prog1'
#0 0x000000000183c26c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
(/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x183c26c)
...
#7 0x00000000017c375e (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x17c375e)
#8 0x00000000016a75c5 llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*)
(/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16a75c5)
#9 0x00000000016ab4f8 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*,
unsigned int) (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16ab4f8)
...
Aborted (core dumped) | llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
The reason is due to llvm change https://reviews.llvm.org/D87153
where the CORE relocation global generation is moved from the beginning
of target dependent optimization (llc) to the beginning
of target independent optimization (opt).
Since samples/bpf programs did not use vmlinux.h and its clang compilation
uses native architecture, we need to adjust arch triple at opt level
to do CORE relocation global generation properly. Otherwise, the above
error will appear.
This patch fixed the issue by introduce opt and llvm-dis to compilation chain,
which will do proper CORE relocation global generation as well as O2 level
optimization. Tested with llvm10, llvm11 and trunk/llvm12.
Signed-off-by: Yonghong Song <yhs@fb.com>
---
samples/bpf/Makefile | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 4f1ed0e3cf9f..79c5fdea63d2 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -211,6 +211,8 @@ TPROGLDLIBS_xsk_fwd += -pthread
# make M=samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
LLC ?= llc
CLANG ?= clang
+OPT ?= opt
+LLVM_DIS ?= llvm-dis
LLVM_OBJCOPY ?= llvm-objcopy
BTF_PAHOLE ?= pahole
@@ -314,7 +316,9 @@ $(obj)/%.o: $(src)/%.c
-Wno-address-of-packed-member -Wno-tautological-compare \
-Wno-unknown-warning-option $(CLANG_ARCH_ARGS) \
-I$(srctree)/samples/bpf/ -include asm_goto_workaround.h \
- -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
+ -O2 -emit-llvm -Xclang -disable-llvm-passes -c $< -o - | \
+ $(OPT) -O2 -mtriple=bpf-pc-linux | $(LLVM_DIS) | \
+ $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
ifeq ($(DWARF2BTF),y)
$(BTF_PAHOLE) -J $@
endif
--
2.24.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH bpf-next 2/2] samples/bpf: fix a compilation error with fallthrough marking
2020-10-03 2:19 [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm Yonghong Song
@ 2020-10-03 2:19 ` Yonghong Song
2020-10-03 4:22 ` [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm Andrii Nakryiko
1 sibling, 0 replies; 6+ messages in thread
From: Yonghong Song @ 2020-10-03 2:19 UTC (permalink / raw)
To: bpf, netdev; +Cc: Alexei Starovoitov, Daniel Borkmann, kernel-team
Compiling samples/bpf hits an error related to fallthrough marking.
...
CC samples/bpf/hbm.o
samples/bpf/hbm.c: In function ‘main’:
samples/bpf/hbm.c:486:4: error: ‘fallthrough’ undeclared (first use in this function)
fallthrough;
^~~~~~~~~~~
The "fallthrough" is not defined under tools/include directory.
Rather, it is "__fallthrough" is defined in linux/compiler.h.
Including "linux/compiler.h" and using "__fallthrough" fixed the issue.
Signed-off-by: Yonghong Song <yhs@fb.com>
---
samples/bpf/hbm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/samples/bpf/hbm.c b/samples/bpf/hbm.c
index 4b22ace52f80..ff4c533dfac2 100644
--- a/samples/bpf/hbm.c
+++ b/samples/bpf/hbm.c
@@ -40,6 +40,7 @@
#include <errno.h>
#include <fcntl.h>
#include <linux/unistd.h>
+#include <linux/compiler.h>
#include <linux/bpf.h>
#include <bpf/bpf.h>
@@ -483,7 +484,7 @@ int main(int argc, char **argv)
"Option -%c requires an argument.\n\n",
optopt);
case 'h':
- fallthrough;
+ __fallthrough;
default:
Usage();
return 0;
--
2.24.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm
2020-10-03 2:19 [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm Yonghong Song
2020-10-03 2:19 ` [PATCH bpf-next 2/2] samples/bpf: fix a compilation error with fallthrough marking Yonghong Song
@ 2020-10-03 4:22 ` Andrii Nakryiko
2020-10-03 5:15 ` Yonghong Song
1 sibling, 1 reply; 6+ messages in thread
From: Andrii Nakryiko @ 2020-10-03 4:22 UTC (permalink / raw)
To: Yonghong Song
Cc: bpf, Networking, Alexei Starovoitov, Daniel Borkmann, Kernel Team
On Fri, Oct 2, 2020 at 7:19 PM Yonghong Song <yhs@fb.com> wrote:
>
> With latest llvm trunk, bpf programs under samples/bpf
> directory, if using CORE, may experience the following
> errors:
>
> LLVM ERROR: Cannot select: intrinsic %llvm.preserve.struct.access.index
> PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
> Stack dump:
> 0. Program arguments: llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
> 1. Running pass 'Function Pass Manager' on module '<stdin>'.
> 2. Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@bpf_prog1'
> #0 0x000000000183c26c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x183c26c)
> ...
> #7 0x00000000017c375e (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x17c375e)
> #8 0x00000000016a75c5 llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*)
> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16a75c5)
> #9 0x00000000016ab4f8 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*,
> unsigned int) (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16ab4f8)
> ...
> Aborted (core dumped) | llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
>
> The reason is due to llvm change https://reviews.llvm.org/D87153
> where the CORE relocation global generation is moved from the beginning
> of target dependent optimization (llc) to the beginning
> of target independent optimization (opt).
>
> Since samples/bpf programs did not use vmlinux.h and its clang compilation
> uses native architecture, we need to adjust arch triple at opt level
> to do CORE relocation global generation properly. Otherwise, the above
> error will appear.
>
> This patch fixed the issue by introduce opt and llvm-dis to compilation chain,
> which will do proper CORE relocation global generation as well as O2 level
> optimization. Tested with llvm10, llvm11 and trunk/llvm12.
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
> samples/bpf/Makefile | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 4f1ed0e3cf9f..79c5fdea63d2 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile
> @@ -211,6 +211,8 @@ TPROGLDLIBS_xsk_fwd += -pthread
> # make M=samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
> LLC ?= llc
> CLANG ?= clang
> +OPT ?= opt
> +LLVM_DIS ?= llvm-dis
> LLVM_OBJCOPY ?= llvm-objcopy
> BTF_PAHOLE ?= pahole
>
> @@ -314,7 +316,9 @@ $(obj)/%.o: $(src)/%.c
> -Wno-address-of-packed-member -Wno-tautological-compare \
> -Wno-unknown-warning-option $(CLANG_ARCH_ARGS) \
> -I$(srctree)/samples/bpf/ -include asm_goto_workaround.h \
> - -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
> + -O2 -emit-llvm -Xclang -disable-llvm-passes -c $< -o - | \
> + $(OPT) -O2 -mtriple=bpf-pc-linux | $(LLVM_DIS) | \
> + $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
I keep forgetting exact details of why we do this native clang + llc
pipeline instead of just doing `clang -target bpf`? Is it still
relevant and necessary, or we can just simplify it now?
> ifeq ($(DWARF2BTF),y)
> $(BTF_PAHOLE) -J $@
> endif
> --
> 2.24.1
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm
2020-10-03 4:22 ` [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm Andrii Nakryiko
@ 2020-10-03 5:15 ` Yonghong Song
2020-10-05 19:27 ` Andrii Nakryiko
0 siblings, 1 reply; 6+ messages in thread
From: Yonghong Song @ 2020-10-03 5:15 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: bpf, Networking, Alexei Starovoitov, Daniel Borkmann, Kernel Team
On 10/2/20 9:22 PM, Andrii Nakryiko wrote:
> On Fri, Oct 2, 2020 at 7:19 PM Yonghong Song <yhs@fb.com> wrote:
>>
>> With latest llvm trunk, bpf programs under samples/bpf
>> directory, if using CORE, may experience the following
>> errors:
>>
>> LLVM ERROR: Cannot select: intrinsic %llvm.preserve.struct.access.index
>> PLEASE submit a bug report to https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=BwTAvhipPl-Az_WaiJDbqU8yl__NvG8W4HmCqWqHdqg&e= and include the crash backtrace.
>> Stack dump:
>> 0. Program arguments: llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
>> 1. Running pass 'Function Pass Manager' on module '<stdin>'.
>> 2. Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@bpf_prog1'
>> #0 0x000000000183c26c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
>> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x183c26c)
>> ...
>> #7 0x00000000017c375e (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x17c375e)
>> #8 0x00000000016a75c5 llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*)
>> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16a75c5)
>> #9 0x00000000016ab4f8 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*,
>> unsigned int) (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16ab4f8)
>> ...
>> Aborted (core dumped) | llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
>>
>> The reason is due to llvm change https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D87153&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=fo_LvXqHJx_m0m0pJJiDdOUcOzVXm2_iYoxPhpqpzng&e=
>> where the CORE relocation global generation is moved from the beginning
>> of target dependent optimization (llc) to the beginning
>> of target independent optimization (opt).
>>
>> Since samples/bpf programs did not use vmlinux.h and its clang compilation
>> uses native architecture, we need to adjust arch triple at opt level
>> to do CORE relocation global generation properly. Otherwise, the above
>> error will appear.
>>
>> This patch fixed the issue by introduce opt and llvm-dis to compilation chain,
>> which will do proper CORE relocation global generation as well as O2 level
>> optimization. Tested with llvm10, llvm11 and trunk/llvm12.
>>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>> ---
>> samples/bpf/Makefile | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
>> index 4f1ed0e3cf9f..79c5fdea63d2 100644
>> --- a/samples/bpf/Makefile
>> +++ b/samples/bpf/Makefile
>> @@ -211,6 +211,8 @@ TPROGLDLIBS_xsk_fwd += -pthread
>> # make M=samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
>> LLC ?= llc
>> CLANG ?= clang
>> +OPT ?= opt
>> +LLVM_DIS ?= llvm-dis
>> LLVM_OBJCOPY ?= llvm-objcopy
>> BTF_PAHOLE ?= pahole
>>
>> @@ -314,7 +316,9 @@ $(obj)/%.o: $(src)/%.c
>> -Wno-address-of-packed-member -Wno-tautological-compare \
>> -Wno-unknown-warning-option $(CLANG_ARCH_ARGS) \
>> -I$(srctree)/samples/bpf/ -include asm_goto_workaround.h \
>> - -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
>> + -O2 -emit-llvm -Xclang -disable-llvm-passes -c $< -o - | \
>> + $(OPT) -O2 -mtriple=bpf-pc-linux | $(LLVM_DIS) | \
>> + $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
>
> I keep forgetting exact details of why we do this native clang + llc
> pipeline instead of just doing `clang -target bpf`? Is it still
samples/bpf programs did not use vmlinux.h. they directly use
kernel-devel headers, hence they need to first compile with native arch
for clang but later change target arch to bpf to generate final byte code.
They cannot just do 'clang -target bpf' without vmlinux.h.
But changing to use vmlinux.h is a much bigger project and I merely
want to make it just work so people won't make/compile samples/bpf
and get compilation errors.
> relevant and necessary, or we can just simplify it now?
>
>> ifeq ($(DWARF2BTF),y)
>> $(BTF_PAHOLE) -J $@
>> endif
>> --
>> 2.24.1
>>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm
2020-10-03 5:15 ` Yonghong Song
@ 2020-10-05 19:27 ` Andrii Nakryiko
2020-10-06 3:05 ` Yonghong Song
0 siblings, 1 reply; 6+ messages in thread
From: Andrii Nakryiko @ 2020-10-05 19:27 UTC (permalink / raw)
To: Yonghong Song
Cc: bpf, Networking, Alexei Starovoitov, Daniel Borkmann, Kernel Team
On Fri, Oct 2, 2020 at 10:16 PM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 10/2/20 9:22 PM, Andrii Nakryiko wrote:
> > On Fri, Oct 2, 2020 at 7:19 PM Yonghong Song <yhs@fb.com> wrote:
> >>
> >> With latest llvm trunk, bpf programs under samples/bpf
> >> directory, if using CORE, may experience the following
> >> errors:
> >>
> >> LLVM ERROR: Cannot select: intrinsic %llvm.preserve.struct.access.index
> >> PLEASE submit a bug report to https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=BwTAvhipPl-Az_WaiJDbqU8yl__NvG8W4HmCqWqHdqg&e= and include the crash backtrace.
> >> Stack dump:
> >> 0. Program arguments: llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
> >> 1. Running pass 'Function Pass Manager' on module '<stdin>'.
> >> 2. Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@bpf_prog1'
> >> #0 0x000000000183c26c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
> >> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x183c26c)
> >> ...
> >> #7 0x00000000017c375e (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x17c375e)
> >> #8 0x00000000016a75c5 llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*)
> >> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16a75c5)
> >> #9 0x00000000016ab4f8 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*,
> >> unsigned int) (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16ab4f8)
> >> ...
> >> Aborted (core dumped) | llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
> >>
> >> The reason is due to llvm change https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D87153&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=fo_LvXqHJx_m0m0pJJiDdOUcOzVXm2_iYoxPhpqpzng&e=
> >> where the CORE relocation global generation is moved from the beginning
> >> of target dependent optimization (llc) to the beginning
> >> of target independent optimization (opt).
> >>
> >> Since samples/bpf programs did not use vmlinux.h and its clang compilation
> >> uses native architecture, we need to adjust arch triple at opt level
> >> to do CORE relocation global generation properly. Otherwise, the above
> >> error will appear.
> >>
> >> This patch fixed the issue by introduce opt and llvm-dis to compilation chain,
> >> which will do proper CORE relocation global generation as well as O2 level
> >> optimization. Tested with llvm10, llvm11 and trunk/llvm12.
> >>
> >> Signed-off-by: Yonghong Song <yhs@fb.com>
> >> ---
> >> samples/bpf/Makefile | 6 +++++-
> >> 1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> >> index 4f1ed0e3cf9f..79c5fdea63d2 100644
> >> --- a/samples/bpf/Makefile
> >> +++ b/samples/bpf/Makefile
> >> @@ -211,6 +211,8 @@ TPROGLDLIBS_xsk_fwd += -pthread
> >> # make M=samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
> >> LLC ?= llc
> >> CLANG ?= clang
> >> +OPT ?= opt
> >> +LLVM_DIS ?= llvm-dis
> >> LLVM_OBJCOPY ?= llvm-objcopy
> >> BTF_PAHOLE ?= pahole
> >>
> >> @@ -314,7 +316,9 @@ $(obj)/%.o: $(src)/%.c
> >> -Wno-address-of-packed-member -Wno-tautological-compare \
> >> -Wno-unknown-warning-option $(CLANG_ARCH_ARGS) \
> >> -I$(srctree)/samples/bpf/ -include asm_goto_workaround.h \
> >> - -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
> >> + -O2 -emit-llvm -Xclang -disable-llvm-passes -c $< -o - | \
> >> + $(OPT) -O2 -mtriple=bpf-pc-linux | $(LLVM_DIS) | \
> >> + $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
This is an extremely unusual set of steps, and might be worthwhile to
leave a comment explaining what's going on, so that I or someone else
doesn't ask the same question few months later :)
At any rate, this fixes the issue, so:
Acked-by: Andrii Nakryiko <andrii@kernel.org>
> >
> > I keep forgetting exact details of why we do this native clang + llc
> > pipeline instead of just doing `clang -target bpf`? Is it still
>
> samples/bpf programs did not use vmlinux.h. they directly use
> kernel-devel headers, hence they need to first compile with native arch
> for clang but later change target arch to bpf to generate final byte code.
> They cannot just do 'clang -target bpf' without vmlinux.h.
Ok, right, thanks for explanation. I wonder if this "native" clang +
llc pass will also help with vmlinux.h on 32-bit architectures (though
with my recent patches that shouldn't be necessary, so this is more of
a curiosity, rather than the need).
>
> But changing to use vmlinux.h is a much bigger project and I merely
> want to make it just work so people won't make/compile samples/bpf
> and get compilation errors.
Right, of course.
>
> > relevant and necessary, or we can just simplify it now?
> >
> >> ifeq ($(DWARF2BTF),y)
> >> $(BTF_PAHOLE) -J $@
> >> endif
> >> --
> >> 2.24.1
> >>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm
2020-10-05 19:27 ` Andrii Nakryiko
@ 2020-10-06 3:05 ` Yonghong Song
0 siblings, 0 replies; 6+ messages in thread
From: Yonghong Song @ 2020-10-06 3:05 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: bpf, Networking, Alexei Starovoitov, Daniel Borkmann, Kernel Team
On 10/5/20 12:27 PM, Andrii Nakryiko wrote:
> On Fri, Oct 2, 2020 at 10:16 PM Yonghong Song <yhs@fb.com> wrote:
>>
>>
>>
>> On 10/2/20 9:22 PM, Andrii Nakryiko wrote:
>>> On Fri, Oct 2, 2020 at 7:19 PM Yonghong Song <yhs@fb.com> wrote:
>>>>
>>>> With latest llvm trunk, bpf programs under samples/bpf
>>>> directory, if using CORE, may experience the following
>>>> errors:
>>>>
>>>> LLVM ERROR: Cannot select: intrinsic %llvm.preserve.struct.access.index
>>>> PLEASE submit a bug report to https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=BwTAvhipPl-Az_WaiJDbqU8yl__NvG8W4HmCqWqHdqg&e= and include the crash backtrace.
>>>> Stack dump:
>>>> 0. Program arguments: llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
>>>> 1. Running pass 'Function Pass Manager' on module '<stdin>'.
>>>> 2. Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@bpf_prog1'
>>>> #0 0x000000000183c26c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int)
>>>> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x183c26c)
>>>> ...
>>>> #7 0x00000000017c375e (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x17c375e)
>>>> #8 0x00000000016a75c5 llvm::SelectionDAGISel::CannotYetSelect(llvm::SDNode*)
>>>> (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16a75c5)
>>>> #9 0x00000000016ab4f8 llvm::SelectionDAGISel::SelectCodeCommon(llvm::SDNode*, unsigned char const*,
>>>> unsigned int) (/data/users/yhs/work/llvm-project/llvm/build.cur/install/bin/llc+0x16ab4f8)
>>>> ...
>>>> Aborted (core dumped) | llc -march=bpf -filetype=obj -o samples/bpf/test_probe_write_user_kern.o
>>>>
>>>> The reason is due to llvm change https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D87153&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=_D9tvuWQ6EbYqcMBdVB0qqRMVdV6Etws5ITtx8Pa1ZM&s=fo_LvXqHJx_m0m0pJJiDdOUcOzVXm2_iYoxPhpqpzng&e=
>>>> where the CORE relocation global generation is moved from the beginning
>>>> of target dependent optimization (llc) to the beginning
>>>> of target independent optimization (opt).
>>>>
>>>> Since samples/bpf programs did not use vmlinux.h and its clang compilation
>>>> uses native architecture, we need to adjust arch triple at opt level
>>>> to do CORE relocation global generation properly. Otherwise, the above
>>>> error will appear.
>>>>
>>>> This patch fixed the issue by introduce opt and llvm-dis to compilation chain,
>>>> which will do proper CORE relocation global generation as well as O2 level
>>>> optimization. Tested with llvm10, llvm11 and trunk/llvm12.
>>>>
>>>> Signed-off-by: Yonghong Song <yhs@fb.com>
>>>> ---
>>>> samples/bpf/Makefile | 6 +++++-
>>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
>>>> index 4f1ed0e3cf9f..79c5fdea63d2 100644
>>>> --- a/samples/bpf/Makefile
>>>> +++ b/samples/bpf/Makefile
>>>> @@ -211,6 +211,8 @@ TPROGLDLIBS_xsk_fwd += -pthread
>>>> # make M=samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
>>>> LLC ?= llc
>>>> CLANG ?= clang
>>>> +OPT ?= opt
>>>> +LLVM_DIS ?= llvm-dis
>>>> LLVM_OBJCOPY ?= llvm-objcopy
>>>> BTF_PAHOLE ?= pahole
>>>>
>>>> @@ -314,7 +316,9 @@ $(obj)/%.o: $(src)/%.c
>>>> -Wno-address-of-packed-member -Wno-tautological-compare \
>>>> -Wno-unknown-warning-option $(CLANG_ARCH_ARGS) \
>>>> -I$(srctree)/samples/bpf/ -include asm_goto_workaround.h \
>>>> - -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
>>>> + -O2 -emit-llvm -Xclang -disable-llvm-passes -c $< -o - | \
>>>> + $(OPT) -O2 -mtriple=bpf-pc-linux | $(LLVM_DIS) | \
>>>> + $(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@
>
> This is an extremely unusual set of steps, and might be worthwhile to
> leave a comment explaining what's going on, so that I or someone else
> doesn't ask the same question few months later :)
Sure. Will add some comments and send v2.
>
> At any rate, this fixes the issue, so:
>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
>
>>>
>>> I keep forgetting exact details of why we do this native clang + llc
>>> pipeline instead of just doing `clang -target bpf`? Is it still
>>
>> samples/bpf programs did not use vmlinux.h. they directly use
>> kernel-devel headers, hence they need to first compile with native arch
>> for clang but later change target arch to bpf to generate final byte code.
>> They cannot just do 'clang -target bpf' without vmlinux.h.
>
> Ok, right, thanks for explanation. I wonder if this "native" clang +
> llc pass will also help with vmlinux.h on 32-bit architectures (though
> with my recent patches that shouldn't be necessary, so this is more of
> a curiosity, rather than the need).
Yes, I think this should help 32-bit as all the 32-bit long/ptr size is
captured in IR. I probably tried before with 32bit x86 uprobe, but I
forgot details...
>
>>
>> But changing to use vmlinux.h is a much bigger project and I merely
>> want to make it just work so people won't make/compile samples/bpf
>> and get compilation errors.
>
> Right, of course.
>
>>
>>> relevant and necessary, or we can just simplify it now?
>>>
>>>> ifeq ($(DWARF2BTF),y)
>>>> $(BTF_PAHOLE) -J $@
>>>> endif
>>>> --
>>>> 2.24.1
>>>>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-10-06 3:06 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-10-03 2:19 [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm Yonghong Song
2020-10-03 2:19 ` [PATCH bpf-next 2/2] samples/bpf: fix a compilation error with fallthrough marking Yonghong Song
2020-10-03 4:22 ` [PATCH bpf-next 1/2] samples/bpf: change Makefile to cope with latest llvm Andrii Nakryiko
2020-10-03 5:15 ` Yonghong Song
2020-10-05 19:27 ` Andrii Nakryiko
2020-10-06 3:05 ` Yonghong Song
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).