Message-ID: <CAK7LNARqnhZuDf75_juBtdK0GV8jL_aDjnuyU=-8zjdCZetF1g@mail.gmail.com>
Date: Mon, 21 Oct 2024 11:15:07 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Rong Xu <xur@...gle.com>
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 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 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.





> +               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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