linux-kernel - Re: [PATCH v3] checkpatch: add warning for avoiding .L prefix symbols in assembly files

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Message-ID: <a7329e5d5661ed6478a7eb33db854a6357447c16.camel@perches.com>
Date:   Sat, 23 Jan 2021 13:01:42 -0800
From:   Joe Perches <joe@...ches.com>
To:     Aditya Srivastava <yashsri421@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     lukas.bulwahn@...il.com, dwaipayanray1@...il.com,
        broonie@...nel.org, ndesaulniers@...gle.com, jpoimboe@...hat.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] checkpatch: add warning for avoiding .L prefix
 symbols in assembly files

On Sun, 2021-01-24 at 00:34 +0530, Aditya Srivastava wrote:
> objtool requires that all code must be contained in an ELF symbol.
> Symbol names that have a '.L' prefix do not emit symbol table entries, as
> they have special meaning for the assembler.
> 
> '.L' prefixed symbols can be used within a code region, but should be
> avoided for denoting a range of code via 'SYM_*_START/END' annotations.
> 
> Add a new check to emit a warning on finding the usage of '.L' symbols
> for '.S' files, if it denotes range of code via SYM_*_START/END
> annotation pair.
> 
> Suggested-by: Mark Brown <broonie@...nel.org>
> Link: https://lore.kernel.org/lkml/20210112210154.GI4646@sirena.org.uk
> Signed-off-by: Aditya Srivastava <yashsri421@...il.com>

Acked-by: Joe Perches <joe@...ches.com>

> ---
> * Applies perfectly on next-20210122
> 
> Changes in v3:
> - Modify regex for SYM_*_START/END pair
> - remove check for arch/x86/entry/* and arch/x86/lib/*
> - change 'Link:' in commit message to lkml
> - Modify commit description accordingly
> 
> Changes in v2:
> - Reduce the check to only SYM_*_START/END lines
> - Reduce the check for only .S files in arch/x86/entry/* and arch/x86/lib/* as suggested by Josh and Nick
> - Modify commit message
> 
>  scripts/checkpatch.pl | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 7030c4d6d126..4a03326c87b6 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -3590,6 +3590,13 @@ sub process {
>  			}
>  		}
>  
> 
> +# check for .L prefix local symbols in .S files
> +		if ($realfile =~ /\.S$/ &&
> +		    $line =~ /^\+\s*(?:[A-Z]+_)?SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
> +			WARN("AVOID_L_PREFIX",
> +			     "Avoid using '.L' prefixed local symbol names for denoting a range of code via 'SYM_*_START/END' annotations; see Documentation/asm-annotations.rst\n" . $herecurr);
> +		}
> +
>  # check we are in a valid source file C or perl if not then ignore this hunk
>  		next if ($realfile !~ /\.(h|c|pl|dtsi|dts)$/);
>  
>