Message-ID: <44193ca7-9d31-4b58-99cc-3300a6ad5289@gmail.com>
Date: Sat, 9 Nov 2024 16:38:58 +0100
From: Klara Modin <klarasmodin@...il.com>
To: Rong Xu <xur@...gle.com>, 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>,
 Masahiro Yamada <masahiroy@...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>, "David S. Miller"
 <davem@...emloft.net>, Andreas Larsson <andreas@...sler.com>,
 Yonghong Song <yonghong.song@...ux.dev>, Yabin Cui <yabinc@...gle.com>,
 Krzysztof Pszeniczny <kpszeniczny@...gle.com>,
 Sriraman Tallam <tmsriram@...gle.com>, Stephane Eranian <eranian@...gle.com>
Cc: x86@...nel.org, linux-arch@...r.kernel.org, sparclinux@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v6 3/7] Adjust symbol ordering in text output section

Hi,

On 2024-10-26 07:14, 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. 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.

With this patch (622240ea8d71a75055399fd4b3cc2b190e44d2e2 in 
next-20241108) my Edgerouter 6P hangs on boot (Cavium Octeon III, 
mips64, running in big endian). It's using device tree passed from the 
vendored u-boot (attached in case it's relevant).

Disabling dead code elimination does not fix the issue.

Please let me know if there's anything else you need.

Regards,
Klara Modin

> 
> 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>
> Tested-by: Yonghong Song <yonghong.song@...ux.dev>
> Tested-by: Yabin Cui <yabinc@...gle.com>
> Change-Id: I5202d40bc7e24f93c2bfb2f0d987e9dc57dec1b1
> ---
>   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

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