| Message ID | 20241026051410.2819338-4-xur@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add AutoFDO and Propeller support for Clang build | expand |
On Fri, Oct 25, 2024 at 10:14:05PM -0700, Rong Xu wrote: > When the -ffunction-sections compiler option is enabled, each function > is placed in a separate section named .text.function_name rather than > putting all functions in a single .text section. > > However, using -function-sections can cause problems with the > linker script. The comments included in include/asm-generic/vmlinux.lds.h > note these issues.: > “TEXT_MAIN here will match .text.fixup and .text.unlikely if dead > code elimination is enabled, so these sections should be converted > to use ".." first.” > > It is unclear whether there is a straightforward method for converting > a suffix to "..". While I'm not a fan of the potential loss of a page, I'm not aware of a way to do this renaming. If we want to keep these as "cold", then this is probably the best way to do it. > This patch modifies the order of subsections within the text output > section. Specifically, it repositions sections with certain fixed patterns > (for example .text.unlikely) before TEXT_MAIN, ensuring that they are > grouped and matched together. It also places .text.hot section at the > beginning of a page to help the TLB performance. > > Note that the limitation arises because the linker script employs glob > patterns instead of regular expressions for string matching. While there > is a method to maintain the current order using complex patterns, this > significantly complicates the pattern and increases the likelihood of > errors. > > This patch also changes vmlinux.lds.S for the sparc64 architecture to > accommodate specific symbol placement requirements. > > Co-developed-by: Han Shen <shenhan@google.com> > Signed-off-by: Han Shen <shenhan@google.com> > Signed-off-by: Rong Xu <xur@google.com> > Suggested-by: Sriraman Tallam <tmsriram@google.com> > Suggested-by: Krzysztof Pszeniczny <kpszeniczny@google.com> > Tested-by: Yonghong Song <yonghong.song@linux.dev> > Tested-by: Yabin Cui <yabinc@google.com> > Change-Id: I5202d40bc7e24f93c2bfb2f0d987e9dc57dec1b1 Reviewed-by: Kees Cook <kees@kernel.org> -Kees > --- > arch/sparc/kernel/vmlinux.lds.S | 5 +++++ > include/asm-generic/vmlinux.lds.h | 19 ++++++++++++------- > 2 files changed, 17 insertions(+), 7 deletions(-) > > diff --git a/arch/sparc/kernel/vmlinux.lds.S b/arch/sparc/kernel/vmlinux.lds.S > index d317a843f7ea9..f1b86eb303404 100644 > --- a/arch/sparc/kernel/vmlinux.lds.S > +++ b/arch/sparc/kernel/vmlinux.lds.S > @@ -48,6 +48,11 @@ SECTIONS > { > _text = .; > HEAD_TEXT > + ALIGN_FUNCTION(); > +#ifdef CONFIG_SPARC64 > + /* Match text section symbols in head_64.S first */ > + *head_64.o(.text) > +#endif > TEXT_TEXT > SCHED_TEXT > LOCK_TEXT > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index eeadbaeccf88b..fd901951549c0 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -553,19 +553,24 @@ > * .text section. Map to function alignment to avoid address changes > * during second ld run in second ld pass when generating System.map > * > - * TEXT_MAIN here will match .text.fixup and .text.unlikely if dead > - * code elimination is enabled, so these sections should be converted > - * to use ".." first. > + * TEXT_MAIN here will match symbols with a fixed pattern (for example, > + * .text.hot or .text.unlikely) if dead code elimination or > + * function-section is enabled. Match these symbols first before > + * TEXT_MAIN to ensure they are grouped together. > + * > + * Also placing .text.hot section at the beginning of a page, this > + * would help the TLB performance. > */ > #define TEXT_TEXT \ > ALIGN_FUNCTION(); \ > + *(.text.asan.* .text.tsan.*) \ > + *(.text.unknown .text.unknown.*) \ > + *(.text.unlikely .text.unlikely.*) \ > + . = ALIGN(PAGE_SIZE); \ > *(.text.hot .text.hot.*) \ > *(TEXT_MAIN .text.fixup) \ > - *(.text.unlikely .text.unlikely.*) \ > - *(.text.unknown .text.unknown.*) \ > NOINSTR_TEXT \ > - *(.ref.text) \ > - *(.text.asan.* .text.tsan.*) > + *(.ref.text) > > > /* sched.text is aling to function alignment to secure we have same > -- > 2.47.0.163.g1226f6d8fa-goog >
diff --git a/arch/sparc/kernel/vmlinux.lds.S b/arch/sparc/kernel/vmlinux.lds.S index d317a843f7ea9..f1b86eb303404 100644 --- a/arch/sparc/kernel/vmlinux.lds.S +++ b/arch/sparc/kernel/vmlinux.lds.S @@ -48,6 +48,11 @@ SECTIONS { _text = .; HEAD_TEXT + ALIGN_FUNCTION(); +#ifdef CONFIG_SPARC64 + /* Match text section symbols in head_64.S first */ + *head_64.o(.text) +#endif TEXT_TEXT SCHED_TEXT LOCK_TEXT diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index eeadbaeccf88b..fd901951549c0 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -553,19 +553,24 @@ * .text section. Map to function alignment to avoid address changes * during second ld run in second ld pass when generating System.map * - * TEXT_MAIN here will match .text.fixup and .text.unlikely if dead - * code elimination is enabled, so these sections should be converted - * to use ".." first. + * TEXT_MAIN here will match symbols with a fixed pattern (for example, + * .text.hot or .text.unlikely) if dead code elimination or + * function-section is enabled. Match these symbols first before + * TEXT_MAIN to ensure they are grouped together. + * + * Also placing .text.hot section at the beginning of a page, this + * would help the TLB performance. */ #define TEXT_TEXT \ ALIGN_FUNCTION(); \ + *(.text.asan.* .text.tsan.*) \ + *(.text.unknown .text.unknown.*) \ + *(.text.unlikely .text.unlikely.*) \ + . = ALIGN(PAGE_SIZE); \ *(.text.hot .text.hot.*) \ *(TEXT_MAIN .text.fixup) \ - *(.text.unlikely .text.unlikely.*) \ - *(.text.unknown .text.unknown.*) \ NOINSTR_TEXT \ - *(.ref.text) \ - *(.text.asan.* .text.tsan.*) + *(.ref.text) /* sched.text is aling to function alignment to secure we have same