The answers are the same as the reply in [PATCH v4 5/6] On Sun, Oct 20, 2024 at 7:26 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > On Tue, Oct 15, 2024 at 6:33 AM Rong Xu <xur@xxxxxxxxxx> wrote: > > > > Enable -ffunction-sections by default for the AutoFDO build. > > > > With -ffunction-sections, the compiler places each function in its own > > section named .text.function_name instead of placing all functions in > > the .text section. In the AutoFDO build, this allows the linker to > > utilize profile information to reorganize functions for improved > > utilization of iCache and iTLB. > > > > Co-developed-by: Han Shen <shenhan@xxxxxxxxxx> > > Signed-off-by: Han Shen <shenhan@xxxxxxxxxx> > > Signed-off-by: Rong Xu <xur@xxxxxxxxxx> > > Suggested-by: Sriraman Tallam <tmsriram@xxxxxxxxxx> > > --- > > include/asm-generic/vmlinux.lds.h | 37 ++++++++++++++++++++++++------- > > scripts/Makefile.autofdo | 2 +- > > 2 files changed, 30 insertions(+), 9 deletions(-) > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index 5df589c60401..ace617d1af9b 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -95,18 +95,25 @@ > > * With LTO_CLANG, the linker also splits sections by default, so we need > > * these macros to combine the sections during the final link. > > * > > + * With LTO_CLANG, the linker also splits sections by default, so we need > > + * these macros to combine the sections during the final link. > > + * > > * RODATA_MAIN is not used because existing code already defines .rodata.x > > * sections to be brought in with rodata. > > */ > > -#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_MAIN .text .text.[0-9a-zA-Z_]* > > +#else > > +#define TEXT_MAIN .text > > +#endif > > +#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) > > #define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..L* .data..compoundliteral* .data.$__unnamed_* .data.$L* > > #define SDATA_MAIN .sdata .sdata.[0-9a-zA-Z_]* > > #define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* .rodata..L* > > #define BSS_MAIN .bss .bss.[0-9a-zA-Z_]* .bss..L* .bss..compoundliteral* > > #define SBSS_MAIN .sbss .sbss.[0-9a-zA-Z_]* > > #else > > -#define TEXT_MAIN .text > > #define DATA_MAIN .data > > #define SDATA_MAIN .sdata > > #define RODATA_MAIN .rodata > > @@ -549,6 +556,20 @@ > > __cpuidle_text_end = .; \ > > __noinstr_text_end = .; > > > > +#ifdef CONFIG_AUTOFDO_CLANG > > +#define TEXT_HOT \ > > + __hot_text_start = .; \ > > + *(.text.hot .text.hot.*) \ > > + __hot_text_end = .; > > +#define TEXT_UNLIKELY \ > > + __unlikely_text_start = .; \ > > + *(.text.unlikely .text.unlikely.*) \ > > + __unlikely_text_end = .; > > +#else > > +#define TEXT_HOT *(.text.hot .text.hot.*) > > +#define TEXT_UNLIKELY *(.text.unlikely .text.unlikely.*) > > +#endif > > > > 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. > > > 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. > > > > > > > > > > > > > + > > /* > > * .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
