linux-kernel - Re: [PATCH] kallsyms: ignore local block labels generated by compiler

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Message-ID: <20220128152147.mwjkf45z72qwdikq@mail.google.com>
Date:   Fri, 28 Jan 2022 23:21:47 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] kallsyms: ignore local block labels generated by compiler

On Fri, Jan 28, 2022 at 06:57:46PM +0800, Changbin Du wrote:
> The llvm compiler can generate lots of local block labels and they might
> overlap with C defined symbols. So let's ignore such local labels.
> 
> Before this change, dumpstack shows a local symbol for epc:
> [    0.040341][    T0] Hardware name: riscv-virtio,qemu (DT)
> [    0.040376][    T0] epc : .LBB6_14+0x22/0x6a
> [    0.040452][    T0]  ra : restore_all+0x12/0x6e
> 
> After this change, the C defined symbol is shown which is expected:
> [    0.035795][    T0] Hardware name: riscv-virtio,qemu (DT)
> [    0.036332][    T0] epc : trace_hardirqs_on+0x54/0x13c
> [    0.036567][    T0]  ra : restore_all+0x12/0x6e
> 
> Signed-off-by: Changbin Du <changbin.du@...il.com>
> ---
>  scripts/kallsyms.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 54ad86d13784..5f4be9d72a32 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -108,6 +108,7 @@ static bool is_ignored_symbol(const char *name, char type)
>  	/* Symbol names that begin with the following are ignored.*/
>  	static const char * const ignored_prefixes[] = {
>  		"$",			/* local symbols for ARM, MIPS, etc. */
> +		".LBB",			/* local block labels generated by compiler */
I aslo found many symbols like '.Ltmpxxx', '.L__unnamed_xx'. So should we just
ignore all symbols prefixed by '.L'?

>  		".LASANPC",		/* s390 kasan local symbols */
>  		"__crc_",		/* modversions */
>  		"__efistub_",		/* arm64 EFI stub namespace */
> -- 
> 2.32.0
> 

-- 
Cheers,
Changbin Du