linux-kernel - Re: [PATCH] kallsyms: ignore all local labels prefixed by '.L'

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Date:   Thu, 3 Feb 2022 09:01:23 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Changbin Du <changbin.du@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] kallsyms: ignore all local labels prefixed by '.L'

On Tue, Feb 01, 2022 at 11:42:59AM -0800, Nick Desaulniers wrote:
> On Mon, Jan 31, 2022 at 5:33 PM Changbin Du <changbin.du@...il.com> wrote:
> 
> Make sure to mark the version of your patches (this is v2, IIUC). `git
> format-patch -v2 HEAD~`
>
Sure, I fogot to add version NO. this time. Thanks for your reminding.

> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> 
> >
> > The llvm compiler can generate lots of local labels ('.LBB', '.Ltmpxxx',
> > '.L__unnamed_xx', etc.). These symbols usually are useless for debugging.
> > And they might overlap with handwritten symbols.
> >
> > Before this change, a dumpstack shows a local symbol for epc:
> > [    0.040341][    T0] Hardware name: riscv-virtio,qemu (DT)
> > [    0.040376][    T0] epc : .LBB6_14+0x22/0x6a
> > [    0.040452][    T0]  ra : restore_all+0x12/0x6e
> >
> > The simple solution is that we can ignore all local labels prefixed by '.L'.
> > For handwritten symbols which need to be preserved should drop the '.L'
> > prefix.
> >
> > After this change, the C defined symbol is shown so we can locate the
> > problematical code immediately:
> > [    0.035795][    T0] Hardware name: riscv-virtio,qemu (DT)
> > [    0.036332][    T0] epc : trace_hardirqs_on+0x54/0x13c
> > [    0.036567][    T0]  ra : restore_all+0x12/0x6e
> >
> > Signed-off-by: Changbin Du <changbin.du@...il.com>
> > ---
> >  scripts/kallsyms.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> > index 54ad86d13784..8caabddf817c 100644
> > --- a/scripts/kallsyms.c
> > +++ b/scripts/kallsyms.c
> > @@ -108,7 +108,7 @@ static bool is_ignored_symbol(const char *name, char type)
> >         /* Symbol names that begin with the following are ignored.*/
> >         static const char * const ignored_prefixes[] = {
> >                 "$",                    /* local symbols for ARM, MIPS, etc. */
> > -               ".LASANPC",             /* s390 kasan local symbols */
> > +               ".L",                   /* local labels, .LBB,.Ltmpxxx,.L__unnamed_xx,.LASANPC, etc. */
> >                 "__crc_",               /* modversions */
> >                 "__efistub_",           /* arm64 EFI stub namespace */
> >                 "__kvm_nvhe_",          /* arm64 non-VHE KVM namespace */
> > --
> > 2.32.0
> >
> 
> 
> -- 
> Thanks,
> ~Nick Desaulniers

-- 
Cheers,
Changbin Du