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Message-ID: <CAF1bQ=S1Hv=fJxk38dYkRTAXWQO_4W8QLTfbNRbihg8UvUKvGQ@mail.gmail.com> Date: Mon, 21 Oct 2024 16:43:12 -0700 From: Rong Xu <xur@...gle.com> To: Masahiro Yamada <masahiroy@...nel.org> Cc: Alice Ryhl <aliceryhl@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Arnd Bergmann <arnd@...db.de>, Bill Wendling <morbo@...gle.com>, Borislav Petkov <bp@...en8.de>, Breno Leitao <leitao@...ian.org>, Brian Gerst <brgerst@...il.com>, Dave Hansen <dave.hansen@...ux.intel.com>, David Li <davidxl@...gle.com>, Han Shen <shenhan@...gle.com>, Heiko Carstens <hca@...ux.ibm.com>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Josh Poimboeuf <jpoimboe@...nel.org>, Juergen Gross <jgross@...e.com>, Justin Stitt <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>, "Mike Rapoport (IBM)" <rppt@...nel.org>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Nicolas Schier <nicolas@...sle.eu>, "Paul E. McKenney" <paulmck@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Sami Tolvanen <samitolvanen@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, Wei Yang <richard.weiyang@...il.com>, workflows@...r.kernel.org, Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Maksim Panchenko <max4bolt@...il.com>, x86@...nel.org, linux-arch@...r.kernel.org, linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, Sriraman Tallam <tmsriram@...gle.com>, Krzysztof Pszeniczny <kpszeniczny@...gle.com> Subject: Re: [PATCH v4 3/6] Change the symbols order when --ffuntion-sections is enabled On Sun, Oct 20, 2024 at 7:15 PM Masahiro Yamada <masahiroy@...nel.org> wrote: > > On Tue, Oct 15, 2024 at 6:33 AM Rong Xu <xur@...gle.com> 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 "..". > > > > Why not for ".text.fixup"? > > $ git grep --name-only '\.text\.fixup' | xargs sed -i > 's/\.text\.fixup/.text..fixup/g' > I did not move .text.fixup because it currently groups together with TEXT_MAIN. Yes. For all the kernel annotated sections, we can replace them with a ".." string. For compiler generate strings, like .unlikely, .hot, and .split, we need a compiler change for that (maybe under an option). The process will be long. Or we can use an extra script, like objcopy to change them? > > > I do not know how to rename other sections that are generated by compilers. > > > > > > 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@...gle.com> > > Signed-off-by: Han Shen <shenhan@...gle.com> > > Signed-off-by: Rong Xu <xur@...gle.com> > > Suggested-by: Sriraman Tallam <tmsriram@...gle.com> > > Suggested-by: Krzysztof Pszeniczny <kpszeniczny@...gle.com> > > --- > > include/asm-generic/vmlinux.lds.h | 17 +++++++++++++++-- > > 1 file changed, 15 insertions(+), 2 deletions(-) > > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > > index eeadbaeccf88..5df589c60401 100644 > > --- a/include/asm-generic/vmlinux.lds.h > > +++ b/include/asm-generic/vmlinux.lds.h > > @@ -554,9 +554,21 @@ > > * 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 \ > > > Why did you do this conditionally? > > You are making this even more unmaintainable. Again, we don't want to change the default build. If you think the change can apply to the default build, we would be happy to remove the condition. > > > > > > > + 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) \ > > + NOINSTR_TEXT \ > > + *(.ref.text) > > +#else > > #define TEXT_TEXT \ > > ALIGN_FUNCTION(); \ > > *(.text.hot .text.hot.*) \ > > @@ -566,6 +578,7 @@ > > NOINSTR_TEXT \ > > *(.ref.text) \ > > *(.text.asan.* .text.tsan.*) > > +#endif > > > > > > /* sched.text is aling to function alignment to secure we have same > > -- > > 2.47.0.rc1.288.g06298d1525-goog > > > > > > > -- > Best Regards > Masahiro Yamada
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