linux-kernel - Re: [PATCH v2] checkpatch: add warning for avoiding .L prefix symbols in assembly files

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Message-ID: <d5eacb78bd354d26725c34d887a75bf1e8f27a04.camel@perches.com>
Date:   Sat, 23 Jan 2021 09:21:02 -0800
From:   Joe Perches <joe@...ches.com>
To:     Aditya Srivastava <yashsri421@...il.com>,
        linux-kernel@...r.kernel.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
Subject: Re: [PATCH v2] checkpatch: add warning for avoiding .L prefix
 symbols in assembly files

On Sat, 2021-01-23 at 20:44 +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 in arch/x86/entry/* and arch/x86/lib/*, if it denotes
> range of code via SYM_*_START/END annotation pair.
> 
> Suggested-by: Mark Brown <broonie@...nel.org>
> Link: https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/4staOlf-CgAJ

Please do not use groups.google.com links, or if you must, please
use links that are readable.

For instance, this is a better link as it shows the context without
struggling with the poor interface:

https://groups.google.com/g/clang-built-linux/c/E-naBMt_1SM

> Signed-off-by: Aditya Srivastava <yashsri421@...il.com>
> ---
> * Applies perfectly on next-20210122
> 
> 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

I think that's unnecessary.

> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -3590,6 +3590,13 @@ sub process {
>  			}
>  		}
>  
> 
> +# check for .L prefix local symbols in .S files
> +		if ($realfile =~ m@...ch/x86/(?:entry|lib)/.*\.S$@ &&

Using /.S$/ should be enough

> +		    $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {

This might need to be

+		    $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);
> +		}
> +