linux-kernel - Re: [PATCH] tools/objtool: tolerate STT

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Date:   Tue, 20 Dec 2022 14:21:48 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tools/objtool: tolerate STT_NOTYPE symbols at end of
 section



Le 20/12/2022 à 11:13, Nicholas Piggin a écrit :
> Hand-written asm often contains non-function symbols in executable
> sections. _end symbols for finding the size of instruction blocks
> for runtime processing is one such usage.
> 
> optprobe_template_end is one example that causes the warning:
> 
>    objtool: optprobe_template_end(): can't find starting instruction
> 
> This is because the symbol happens to be at the end of the file (and
> therefore end of a section in the object file).
> 
> So ignore end-of-section STT_NOTYPE symbols instead of bailing out
> because an instruction can't be found. While we're here, add a more
> descriptive warning for STT_FUNC symbols found at the end of a
> section.

There's a patch to solve this already as far as I understand. They seem 
different.

See 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20221208072813.25799-1-sv@linux.ibm.com/

> 
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> ---
>   tools/objtool/check.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 4350be739f4f..4b7c8b33069e 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -427,6 +427,15 @@ static int decode_instructions(struct objtool_file *file)
>   			if (func->type != STT_NOTYPE && func->type != STT_FUNC)
>   				continue;
>   
> +			if (func->offset == sec->sh.sh_size) {
> +				/* Heuristic: likely an "end" symbol */
> +				if (func->type == STT_NOTYPE)
> +					continue;
> +				WARN("%s(): STT_FUNC at end of section",
> +				     func->name);
> +				return -1;
> +			}
> +
>   			if (func->return_thunk || func->alias != func)
>   				continue;
>