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

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Date:   Sat, 23 Jan 2021 23:53:26 +0530
From:   Aditya <yashsri421@...il.com>
To:     Joe Perches <joe@...ches.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 23/1/21 10:51 pm, Joe Perches wrote:
> 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
> 

Okay, Got it.. I'll use lkml link for the best.

>> 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/) {
> 

Okay.. Thanks. I'll modify the patch accordingly.

Thanks
Aditya
>> +			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);
>> +		}
>> +
> 
>