Re: [PATCH v4 4/6] AutoFDO: Enable -ffunction-sections for the AutoFDO build

[Masahiro Yamada <masahiroy@kernel.org>]

On Tue, Oct 22, 2024 at 8:32 AM Rong Xu <xur@google.com> wrote:
>
> The answers are the same as the reply in [PATCH v4 5/6]

> >
> >
> > Again, why is this conditional?
>
> The condition is to ensure that we don't change the default kernel
> build by any means. The new code will introduce a few new symbols.
>


Same answer.

I guess you prefer unmaintainable code
because you are not a maintainer.


> >
> > The only difference is *_start and *_end symbols are defined
> > when CONFIG_AUTOFDO_CLANG=y.
> >
> > And, where are these symbols used?
>
> These new symbols are currently unreferenced within the kernel source tree.
> However, they provide a valuable means of identifying hot and cold
> sections of text, and how large they are. I think they are useful information.

OK, then you are doing unrelated changes to
 include/asm-generic/vmlinux.lds.h.

This patch should touch only scripts/Makefile.autofdo

If you want to insert *_start and *_end markers,
you can add a separate patch, explaining your motivation.






>
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > > +
> > >  /*
> > >   * .text section. Map to function alignment to avoid address changes
> > >   * during second ld run in second ld pass when generating System.map
> > > @@ -557,30 +578,30 @@
> > >   * code elimination or function-section is enabled. Match these symbols
> > >   * first when in these builds.
> > >   */
> > > -#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG)
> > > +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
> > > +defined(CONFIG_AUTOFDO_CLANG)
> > >  #define TEXT_TEXT                                                      \
> > >                 ALIGN_FUNCTION();                                       \
> > >                 *(.text.asan.* .text.tsan.*)                            \
> > >                 *(.text.unknown .text.unknown.*)                        \
> > > -               *(.text.unlikely .text.unlikely.*)                      \
> > > +               TEXT_UNLIKELY                                           \
> > >                 . = ALIGN(PAGE_SIZE);                                   \
> > > -               *(.text.hot .text.hot.*)                                \
> > > +               TEXT_HOT                                                \
> > >                 *(TEXT_MAIN .text.fixup)                                \
> > >                 NOINSTR_TEXT                                            \
> > >                 *(.ref.text)
> > >  #else
> > >  #define TEXT_TEXT                                                      \
> > >                 ALIGN_FUNCTION();                                       \
> > > -               *(.text.hot .text.hot.*)                                \
> > > +               TEXT_HOT                                                \
> > >                 *(TEXT_MAIN .text.fixup)                                \
> > > -               *(.text.unlikely .text.unlikely.*)                      \
> > > +               TEXT_UNLIKELY                                           \
> > >                 *(.text.unknown .text.unknown.*)                        \
> > >                 NOINSTR_TEXT                                            \
> > >                 *(.ref.text)                                            \
> > >                 *(.text.asan.* .text.tsan.*)
> > >  #endif
> > >
> > > -
> > >  /* sched.text is aling to function alignment to secure we have same
> > >   * address even at second ld pass when generating System.map */
> > >  #define SCHED_TEXT                                                     \
> > > diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo
> > > index 1c9f224bc221..9c9a530ef090 100644
> > > --- a/scripts/Makefile.autofdo
> > > +++ b/scripts/Makefile.autofdo
> > > @@ -10,7 +10,7 @@ ifndef CONFIG_DEBUG_INFO
> > >  endif
> > >
> > >  ifdef CLANG_AUTOFDO_PROFILE
> > > -  CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE)
> > > +  CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) -ffunction-sections
> > >  endif
> > >
> > >  ifdef CONFIG_LTO_CLANG_THIN
> > > --
> > > 2.47.0.rc1.288.g06298d1525-goog
> > >
> > >
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada
>


--
Best Regards
Masahiro Yamada