* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-17 14:33 [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64 gregory.herrero
@ 2020-07-17 15:18 ` Greg KH
2020-07-17 17:30 ` Steven Rostedt
` (2 subsequent siblings)
3 siblings, 0 replies; 10+ messages in thread
From: Greg KH @ 2020-07-17 15:18 UTC (permalink / raw)
To: gregory.herrero; +Cc: linux-kernel, rostedt, stable
On Fri, Jul 17, 2020 at 04:33:38PM +0200, gregory.herrero@oracle.com wrote:
> From: Gregory Herrero <gregory.herrero@oracle.com>
>
> Currently, if a section has a relocation to '_mcount' symbol, a new
> __mcount_loc entry will be added whatever the relocation type is.
> This is problematic when a relocation to '_mcount' is in the middle of a
> section and is not a call for ftrace use.
>
> Such relocation could be generated with below code for example:
> bool is_mcount(unsigned long addr)
> {
> return (target == (unsigned long) &_mcount);
> }
>
> With this snippet of code, ftrace will try to patch the mcount location
> generated by this code on module load and fail with:
>
> Call trace:
> ftrace_bug+0xa0/0x28c
> ftrace_process_locs+0x2f4/0x430
> ftrace_module_init+0x30/0x38
> load_module+0x14f0/0x1e78
> __do_sys_finit_module+0x100/0x11c
> __arm64_sys_finit_module+0x28/0x34
> el0_svc_common+0x88/0x194
> el0_svc_handler+0x38/0x8c
> el0_svc+0x8/0xc
> ---[ end trace d828d06b36ad9d59 ]---
> ftrace failed to modify
> [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
> actual: 66:a9:3c:90
> Initializing ftrace call sites
> ftrace record flags: 2000000
> (0)
> expected tramp: ffffa2dc6cf66724
>
> So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
> recordmcount.
>
> Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
> Signed-off-by: Gregory Herrero <gregory.herrero@oracle.com>
> ---
> scripts/recordmcount.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> index 7225107a9aaf..e59022b3f125 100644
> --- a/scripts/recordmcount.c
> +++ b/scripts/recordmcount.c
> @@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
> return 1;
> }
>
> +static int arm64_is_fake_mcount(Elf64_Rel const *rp)
> +{
> + return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> +}
> +
> /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
> * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
> * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
> @@ -547,6 +552,7 @@ static int do_file(char const *const fname)
> make_nop = make_nop_arm64;
> rel_type_nop = R_AARCH64_NONE;
> ideal_nop = ideal_nop4_arm64;
> + is_fake_mcount64 = arm64_is_fake_mcount;
> break;
> case EM_IA_64: reltype = R_IA64_IMM64; break;
> case EM_MIPS: /* reltype: e_class */ break;
> --
> 2.27.0
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-17 14:33 [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64 gregory.herrero
2020-07-17 15:18 ` Greg KH
@ 2020-07-17 17:30 ` Steven Rostedt
2020-07-17 20:01 ` Gregory Herrero
2020-07-22 16:36 ` Catalin Marinas
2020-07-23 11:52 ` Mark Rutland
2020-07-24 12:14 ` Catalin Marinas
3 siblings, 2 replies; 10+ messages in thread
From: Steven Rostedt @ 2020-07-17 17:30 UTC (permalink / raw)
To: gregory.herrero
Cc: linux-kernel, stable, Catalin Marinas, Will Deacon, linux-arm-kernel
On Fri, 17 Jul 2020 16:33:38 +0200
gregory.herrero@oracle.com wrote:
> From: Gregory Herrero <gregory.herrero@oracle.com>
>
> Currently, if a section has a relocation to '_mcount' symbol, a new
> __mcount_loc entry will be added whatever the relocation type is.
> This is problematic when a relocation to '_mcount' is in the middle of a
> section and is not a call for ftrace use.
>
> Such relocation could be generated with below code for example:
> bool is_mcount(unsigned long addr)
> {
> return (target == (unsigned long) &_mcount);
> }
>
> With this snippet of code, ftrace will try to patch the mcount location
> generated by this code on module load and fail with:
>
> Call trace:
> ftrace_bug+0xa0/0x28c
> ftrace_process_locs+0x2f4/0x430
> ftrace_module_init+0x30/0x38
> load_module+0x14f0/0x1e78
> __do_sys_finit_module+0x100/0x11c
> __arm64_sys_finit_module+0x28/0x34
> el0_svc_common+0x88/0x194
> el0_svc_handler+0x38/0x8c
> el0_svc+0x8/0xc
> ---[ end trace d828d06b36ad9d59 ]---
> ftrace failed to modify
> [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
> actual: 66:a9:3c:90
> Initializing ftrace call sites
> ftrace record flags: 2000000
> (0)
> expected tramp: ffffa2dc6cf66724
>
> So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
> recordmcount.
>
I'd rather have this go through the arm64 tree, as they can test it
better than I can.
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
> Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
> Signed-off-by: Gregory Herrero <gregory.herrero@oracle.com>
> ---
> scripts/recordmcount.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> index 7225107a9aaf..e59022b3f125 100644
> --- a/scripts/recordmcount.c
> +++ b/scripts/recordmcount.c
> @@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
> return 1;
> }
>
> +static int arm64_is_fake_mcount(Elf64_Rel const *rp)
> +{
> + return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> +}
> +
> /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
> * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
> * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
> @@ -547,6 +552,7 @@ static int do_file(char const *const fname)
> make_nop = make_nop_arm64;
> rel_type_nop = R_AARCH64_NONE;
> ideal_nop = ideal_nop4_arm64;
> + is_fake_mcount64 = arm64_is_fake_mcount;
> break;
> case EM_IA_64: reltype = R_IA64_IMM64; break;
> case EM_MIPS: /* reltype: e_class */ break;
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-17 17:30 ` Steven Rostedt
@ 2020-07-17 20:01 ` Gregory Herrero
2020-07-17 20:15 ` Steven Rostedt
2020-07-22 16:36 ` Catalin Marinas
1 sibling, 1 reply; 10+ messages in thread
From: Gregory Herrero @ 2020-07-17 20:01 UTC (permalink / raw)
To: Steven Rostedt
Cc: linux-kernel, stable, Catalin Marinas, Will Deacon, linux-arm-kernel
On Fri, Jul 17, 2020 at 01:30:03PM -0400, Steven Rostedt wrote:
> On Fri, 17 Jul 2020 16:33:38 +0200
> gregory.herrero@oracle.com wrote:
>
> > From: Gregory Herrero <gregory.herrero@oracle.com>
> >
> > Currently, if a section has a relocation to '_mcount' symbol, a new
> > __mcount_loc entry will be added whatever the relocation type is.
> > This is problematic when a relocation to '_mcount' is in the middle of a
> > section and is not a call for ftrace use.
> >
> > Such relocation could be generated with below code for example:
> > bool is_mcount(unsigned long addr)
> > {
> > return (target == (unsigned long) &_mcount);
> > }
> >
> > With this snippet of code, ftrace will try to patch the mcount location
> > generated by this code on module load and fail with:
> >
> > Call trace:
> > ftrace_bug+0xa0/0x28c
> > ftrace_process_locs+0x2f4/0x430
> > ftrace_module_init+0x30/0x38
> > load_module+0x14f0/0x1e78
> > __do_sys_finit_module+0x100/0x11c
> > __arm64_sys_finit_module+0x28/0x34
> > el0_svc_common+0x88/0x194
> > el0_svc_handler+0x38/0x8c
> > el0_svc+0x8/0xc
> > ---[ end trace d828d06b36ad9d59 ]---
> > ftrace failed to modify
> > [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
> > actual: 66:a9:3c:90
> > Initializing ftrace call sites
> > ftrace record flags: 2000000
> > (0)
> > expected tramp: ffffa2dc6cf66724
> >
> > So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
> > recordmcount.
> >
>
> I'd rather have this go through the arm64 tree, as they can test it
> better than I can.
>
> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
>
> -- Steve
>
Thanks Steve.
Should I send a V2 to add 'Cc: stable@vger.kernel.org' in the commit
description or can someone take care of it when adding the commit to
the tree?
Thanks,
Greg
>
> > Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
> > Signed-off-by: Gregory Herrero <gregory.herrero@oracle.com>
> > ---
> > scripts/recordmcount.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> > index 7225107a9aaf..e59022b3f125 100644
> > --- a/scripts/recordmcount.c
> > +++ b/scripts/recordmcount.c
> > @@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
> > return 1;
> > }
> >
> > +static int arm64_is_fake_mcount(Elf64_Rel const *rp)
> > +{
> > + return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> > +}
> > +
> > /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
> > * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
> > * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
> > @@ -547,6 +552,7 @@ static int do_file(char const *const fname)
> > make_nop = make_nop_arm64;
> > rel_type_nop = R_AARCH64_NONE;
> > ideal_nop = ideal_nop4_arm64;
> > + is_fake_mcount64 = arm64_is_fake_mcount;
> > break;
> > case EM_IA_64: reltype = R_IA64_IMM64; break;
> > case EM_MIPS: /* reltype: e_class */ break;
>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-17 20:01 ` Gregory Herrero
@ 2020-07-17 20:15 ` Steven Rostedt
0 siblings, 0 replies; 10+ messages in thread
From: Steven Rostedt @ 2020-07-17 20:15 UTC (permalink / raw)
To: Gregory Herrero
Cc: linux-kernel, stable, Catalin Marinas, Will Deacon, linux-arm-kernel
On Fri, 17 Jul 2020 22:01:19 +0200
Gregory Herrero <gregory.herrero@oracle.com> wrote:
> Thanks Steve.
> Should I send a V2 to add 'Cc: stable@vger.kernel.org' in the commit
> description or can someone take care of it when adding the commit to
> the tree?
If I was taking it, I would simply add the Cc: stable@vger.kernel.org
to the commit log, and no resend would be needed.
It's up to the ARM64 maintainers to decide in this case.
Cheers,
-- Steve
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-17 17:30 ` Steven Rostedt
2020-07-17 20:01 ` Gregory Herrero
@ 2020-07-22 16:36 ` Catalin Marinas
2020-07-22 18:50 ` Gregory Herrero
1 sibling, 1 reply; 10+ messages in thread
From: Catalin Marinas @ 2020-07-22 16:36 UTC (permalink / raw)
To: Steven Rostedt
Cc: gregory.herrero, linux-kernel, stable, Will Deacon, linux-arm-kernel
On Fri, Jul 17, 2020 at 01:30:03PM -0400, Steven Rostedt wrote:
> On Fri, 17 Jul 2020 16:33:38 +0200
> gregory.herrero@oracle.com wrote:
> > From: Gregory Herrero <gregory.herrero@oracle.com>
> > Currently, if a section has a relocation to '_mcount' symbol, a new
> > __mcount_loc entry will be added whatever the relocation type is.
> > This is problematic when a relocation to '_mcount' is in the middle of a
> > section and is not a call for ftrace use.
> >
> > Such relocation could be generated with below code for example:
> > bool is_mcount(unsigned long addr)
> > {
> > return (target == (unsigned long) &_mcount);
> > }
> >
> > With this snippet of code, ftrace will try to patch the mcount location
> > generated by this code on module load and fail with:
> >
> > Call trace:
> > ftrace_bug+0xa0/0x28c
> > ftrace_process_locs+0x2f4/0x430
> > ftrace_module_init+0x30/0x38
> > load_module+0x14f0/0x1e78
> > __do_sys_finit_module+0x100/0x11c
> > __arm64_sys_finit_module+0x28/0x34
> > el0_svc_common+0x88/0x194
> > el0_svc_handler+0x38/0x8c
> > el0_svc+0x8/0xc
> > ---[ end trace d828d06b36ad9d59 ]---
> > ftrace failed to modify
> > [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
> > actual: 66:a9:3c:90
> > Initializing ftrace call sites
> > ftrace record flags: 2000000
> > (0)
> > expected tramp: ffffa2dc6cf66724
> >
> > So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
> > recordmcount.
>
> I'd rather have this go through the arm64 tree, as they can test it
> better than I can.
>
> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Thanks Steve.
> > Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
This Fixes tag looks wrong. The above commit was for arm32.
--
Catalin
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-22 16:36 ` Catalin Marinas
@ 2020-07-22 18:50 ` Gregory Herrero
0 siblings, 0 replies; 10+ messages in thread
From: Gregory Herrero @ 2020-07-22 18:50 UTC (permalink / raw)
To: Catalin Marinas
Cc: Steven Rostedt, linux-kernel, stable, Will Deacon, linux-arm-kernel
On Wed, Jul 22, 2020 at 05:36:50PM +0100, Catalin Marinas wrote:
> On Fri, Jul 17, 2020 at 01:30:03PM -0400, Steven Rostedt wrote:
> > On Fri, 17 Jul 2020 16:33:38 +0200
> > gregory.herrero@oracle.com wrote:
> > > From: Gregory Herrero <gregory.herrero@oracle.com>
> > > Currently, if a section has a relocation to '_mcount' symbol, a new
> > > __mcount_loc entry will be added whatever the relocation type is.
> > > This is problematic when a relocation to '_mcount' is in the middle of a
> > > section and is not a call for ftrace use.
> > >
> > > Such relocation could be generated with below code for example:
> > > bool is_mcount(unsigned long addr)
> > > {
> > > return (target == (unsigned long) &_mcount);
> > > }
> > >
> > > With this snippet of code, ftrace will try to patch the mcount location
> > > generated by this code on module load and fail with:
> > >
> > > Call trace:
> > > ftrace_bug+0xa0/0x28c
> > > ftrace_process_locs+0x2f4/0x430
> > > ftrace_module_init+0x30/0x38
> > > load_module+0x14f0/0x1e78
> > > __do_sys_finit_module+0x100/0x11c
> > > __arm64_sys_finit_module+0x28/0x34
> > > el0_svc_common+0x88/0x194
> > > el0_svc_handler+0x38/0x8c
> > > el0_svc+0x8/0xc
> > > ---[ end trace d828d06b36ad9d59 ]---
> > > ftrace failed to modify
> > > [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
> > > actual: 66:a9:3c:90
> > > Initializing ftrace call sites
> > > ftrace record flags: 2000000
> > > (0)
> > > expected tramp: ffffa2dc6cf66724
> > >
> > > So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
> > > recordmcount.
> >
> > I'd rather have this go through the arm64 tree, as they can test it
> > better than I can.
> >
> > Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
>
> Thanks Steve.
>
> > > Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
>
> This Fixes tag looks wrong. The above commit was for arm32.
>
Thanks for catching this.
It should be as below instead:
Fixes: af64d2aa872a ("ftrace: Add arm64 support to recordmcount")
Should I send a V2?
Thanks,
Greg
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-17 14:33 [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64 gregory.herrero
2020-07-17 15:18 ` Greg KH
2020-07-17 17:30 ` Steven Rostedt
@ 2020-07-23 11:52 ` Mark Rutland
2020-07-23 12:44 ` Gregory Herrero
2020-07-24 12:14 ` Catalin Marinas
3 siblings, 1 reply; 10+ messages in thread
From: Mark Rutland @ 2020-07-23 11:52 UTC (permalink / raw)
To: gregory.herrero; +Cc: linux-kernel, rostedt, stable, will, catalin.marinas
Hi Gregory,
As a general thing, for patches affecting arm64 could you please Cc the
linx-arm-kernel mailing list (linux-arm-kernel@lists.infradead.org).
Some folk working on arm/arm64 aren't subscribed to LKML, and it means
patches like this may get missed.
On Fri, Jul 17, 2020 at 04:33:38PM +0200, gregory.herrero@oracle.com wrote:
> From: Gregory Herrero <gregory.herrero@oracle.com>
>
> Currently, if a section has a relocation to '_mcount' symbol, a new
> __mcount_loc entry will be added whatever the relocation type is.
> This is problematic when a relocation to '_mcount' is in the middle of a
> section and is not a call for ftrace use.
>
> Such relocation could be generated with below code for example:
> bool is_mcount(unsigned long addr)
> {
> return (target == (unsigned long) &_mcount);
> }
>
> With this snippet of code, ftrace will try to patch the mcount location
> generated by this code on module load and fail with:
>
> Call trace:
> ftrace_bug+0xa0/0x28c
> ftrace_process_locs+0x2f4/0x430
> ftrace_module_init+0x30/0x38
> load_module+0x14f0/0x1e78
> __do_sys_finit_module+0x100/0x11c
> __arm64_sys_finit_module+0x28/0x34
> el0_svc_common+0x88/0x194
> el0_svc_handler+0x38/0x8c
> el0_svc+0x8/0xc
> ---[ end trace d828d06b36ad9d59 ]---
> ftrace failed to modify
> [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
> actual: 66:a9:3c:90
> Initializing ftrace call sites
> ftrace record flags: 2000000
> (0)
> expected tramp: ffffa2dc6cf66724
Which code specifically is this triggering for? Is this something in an
upstream kernel, or out-of-tree patches?
Can you say which toolchain you're using, too?
> So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
> recordmcount.
Given our patching code expects each callsite to be:
bl _mcount
... this looks sane to me, and I *think* that's sound for modules too.
> Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
That's a 32-bit arm commit. I suspect that was meant to be:
Fixes: af64d2aa872a1747 ("ftrace: Add arm64 support to recordmcount")
> Signed-off-by: Gregory Herrero <gregory.herrero@oracle.com>
> ---
> scripts/recordmcount.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> index 7225107a9aaf..e59022b3f125 100644
> --- a/scripts/recordmcount.c
> +++ b/scripts/recordmcount.c
> @@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
> return 1;
> }
>
> +static int arm64_is_fake_mcount(Elf64_Rel const *rp)
> +{
> + return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> +}
> +
> /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
> * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
> * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
> @@ -547,6 +552,7 @@ static int do_file(char const *const fname)
> make_nop = make_nop_arm64;
> rel_type_nop = R_AARCH64_NONE;
> ideal_nop = ideal_nop4_arm64;
> + is_fake_mcount64 = arm64_is_fake_mcount;
> break;
As above, I think this is sound, but if you could answer my questions
that'd be helpful.
Thanks,
Mark.
> case EM_IA_64: reltype = R_IA64_IMM64; break;
> case EM_MIPS: /* reltype: e_class */ break;
> --
> 2.27.0
>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-23 11:52 ` Mark Rutland
@ 2020-07-23 12:44 ` Gregory Herrero
0 siblings, 0 replies; 10+ messages in thread
From: Gregory Herrero @ 2020-07-23 12:44 UTC (permalink / raw)
To: Mark Rutland; +Cc: linux-kernel, rostedt, stable, will, catalin.marinas
Hi Mark,
On Thu, Jul 23, 2020 at 12:52:16PM +0100, Mark Rutland wrote:
> Hi Gregory,
>
> As a general thing, for patches affecting arm64 could you please Cc the
> linx-arm-kernel mailing list (linux-arm-kernel@lists.infradead.org).
> Some folk working on arm/arm64 aren't subscribed to LKML, and it means
> patches like this may get missed.
>
Got it, I will do that next time.
> On Fri, Jul 17, 2020 at 04:33:38PM +0200, gregory.herrero@oracle.com wrote:
> > From: Gregory Herrero <gregory.herrero@oracle.com>
> >
> > Currently, if a section has a relocation to '_mcount' symbol, a new
> > __mcount_loc entry will be added whatever the relocation type is.
> > This is problematic when a relocation to '_mcount' is in the middle of a
> > section and is not a call for ftrace use.
> >
> > Such relocation could be generated with below code for example:
> > bool is_mcount(unsigned long addr)
> > {
> > return (target == (unsigned long) &_mcount);
> > }
> >
> > With this snippet of code, ftrace will try to patch the mcount location
> > generated by this code on module load and fail with:
> >
> > Call trace:
> > ftrace_bug+0xa0/0x28c
> > ftrace_process_locs+0x2f4/0x430
> > ftrace_module_init+0x30/0x38
> > load_module+0x14f0/0x1e78
> > __do_sys_finit_module+0x100/0x11c
> > __arm64_sys_finit_module+0x28/0x34
> > el0_svc_common+0x88/0x194
> > el0_svc_handler+0x38/0x8c
> > el0_svc+0x8/0xc
> > ---[ end trace d828d06b36ad9d59 ]---
> > ftrace failed to modify
> > [<ffffa2dbf3a3a41c>] 0xffffa2dbf3a3a41c
> > actual: 66:a9:3c:90
> > Initializing ftrace call sites
> > ftrace record flags: 2000000
> > (0)
> > expected tramp: ffffa2dc6cf66724
>
> Which code specifically is this triggering for? Is this something in an
> upstream kernel, or out-of-tree patches?
>
We faced this issue while porting Ksplice on ARM64 architecture. So
that's an out-of-tree module. And we got this issue because we have
multiple references to '_mcount' like the one described in the commit
description of this patch.
> Can you say which toolchain you're using, too?
>
We are using native gcc version: gcc (GCC) 7.3.0 20180125 (Red Hat 7.3.0-5)
And native binutils 2.31.1.
> > So Limit the relocation type to R_AARCH64_CALL26 as in perl version of
> > recordmcount.
>
> Given our patching code expects each callsite to be:
>
> bl _mcount
>
> ... this looks sane to me, and I *think* that's sound for modules too.
>
Ok great.
> > Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount")
>
> That's a 32-bit arm commit. I suspect that was meant to be:
>
> Fixes: af64d2aa872a1747 ("ftrace: Add arm64 support to recordmcount")
>
Right.
> > Signed-off-by: Gregory Herrero <gregory.herrero@oracle.com>
> > ---
> > scripts/recordmcount.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
> > index 7225107a9aaf..e59022b3f125 100644
> > --- a/scripts/recordmcount.c
> > +++ b/scripts/recordmcount.c
> > @@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp)
> > return 1;
> > }
> >
> > +static int arm64_is_fake_mcount(Elf64_Rel const *rp)
> > +{
> > + return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26;
> > +}
> > +
> > /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
> > * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
> > * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
> > @@ -547,6 +552,7 @@ static int do_file(char const *const fname)
> > make_nop = make_nop_arm64;
> > rel_type_nop = R_AARCH64_NONE;
> > ideal_nop = ideal_nop4_arm64;
> > + is_fake_mcount64 = arm64_is_fake_mcount;
> > break;
>
> As above, I think this is sound, but if you could answer my questions
> that'd be helpful.
>
Thanks for the review,
Greg
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
2020-07-17 14:33 [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64 gregory.herrero
` (2 preceding siblings ...)
2020-07-23 11:52 ` Mark Rutland
@ 2020-07-24 12:14 ` Catalin Marinas
3 siblings, 0 replies; 10+ messages in thread
From: Catalin Marinas @ 2020-07-24 12:14 UTC (permalink / raw)
To: gregory.herrero, linux-kernel
Cc: Will Deacon, rostedt, Mark Rutland, linux-arm-kernel
On Fri, 17 Jul 2020 16:33:38 +0200, gregory.herrero@oracle.com wrote:
> Currently, if a section has a relocation to '_mcount' symbol, a new
> __mcount_loc entry will be added whatever the relocation type is.
> This is problematic when a relocation to '_mcount' is in the middle of a
> section and is not a call for ftrace use.
>
> Such relocation could be generated with below code for example:
> bool is_mcount(unsigned long addr)
> {
> return (target == (unsigned long) &_mcount);
> }
>
> [...]
Applied to arm64 (for-next/misc), thanks!
[1/1] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64.
https://git.kernel.org/arm64/c/ea0eada45632
--
Catalin
^ permalink raw reply [flat|nested] 10+ messages in thread