On Mon, Jul 29, 2024 at 2:34 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Sun, Jul 28, 2024 at 01:29:56PM -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 "..". This patch modifies the order of subsections within the > > text output section when the -ffunction-sections flag is enabled. > > Specifically, it repositions sections with certain fixed patterns (for > > example .text.unlikely) before TEXT_MAIN, ensuring that they are grouped > > and matched together. > > > > 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. > > > > 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> > > Suggested-by: Krzysztof Pszeniczny <kpszeniczny@xxxxxxxxxx> > > --- > > include/asm-generic/vmlinux.lds.h | 19 ++++++++++++++++--- > > 1 file changed, 16 insertions(+), 3 deletions(-) > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index 5703526d6ebf..f3de66bda293 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -582,9 +582,21 @@ > > * 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. > > + * 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) > > +#define TEXT_TEXT \ > > + *(.text.asan.* .text.tsan.*) \ > > + *(.text.unknown .text.unknown.*) \ > > + *(.text.unlikely .text.unlikely.*) \ > > + ALIGN_FUNCTION(); \ > > Why leave the above text sections unaligned? They are considered cold text. They are not aligned before the change. But I have no objections to making it aligned. (Sorry if you receive a duplicated message. I'm resending this in plain text mode.) > > > + *(.text.hot .text.hot.*) \ > > + *(TEXT_MAIN .text.fixup) \ > > + NOINSTR_TEXT \ > > + *(.ref.text) \ > > + MEM_KEEP(init.text*) > > +#else > > #define TEXT_TEXT \ > > ALIGN_FUNCTION(); \ > > *(.text.hot .text.hot.*) \ > > @@ -594,7 +606,8 @@ > > NOINSTR_TEXT \ > > *(.ref.text) \ > > *(.text.asan.* .text.tsan.*) \ > > - MEM_KEEP(init.text*) \ > > + MEM_KEEP(init.text*) > > +#endif > > > > > > /* sched.text is aling to function alignment to secure we have same > > -- > > 2.46.0.rc1.232.g9752f9e123-goog > >
