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

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Message-ID: <fb1b511d71761c99a9bece803f508b674fce9962.camel@perches.com>
Date:   Wed, 20 Jan 2021 10:43:22 -0800
From:   Joe Perches <joe@...ches.com>
To:     Aditya <yashsri421@...il.com>, linux-kernel@...r.kernel.org
Cc:     lukas.bulwahn@...il.com, dwaipayanray1@...il.com,
        broonie@...nel.org, linux-kernel-mentees@...ts.linuxfoundation.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] checkpatch: add warning for avoiding .L prefix symbols
 in assembly files

On Wed, 2021-01-20 at 18:23 +0530, Aditya wrote:
> On 20/1/21 2:51 pm, Joe Perches wrote:
> > On Wed, 2021-01-20 at 12:55 +0530, Aditya Srivastava wrote:
> > > Local symbols prefixed with '.L' 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
> > > in '.S' files, if it lies within SYM_*_START/END annotation pair.
> > 
> > I believe this needs a test for $file as it won't work well on
> > patches as the SYM_*_START/END may not be in the patch context.
> > 
> Okay.
> 
> > Also, is this supposed to work for local labels like '.L<foo>:'?
> > I don't think a warning should be generated for those.
> > 
> Yes, currently it will generate warning for all symbols which start
> with .L and have non- white character symbol following it, if it is
> lying within SYM_*_START/END annotation pair.
> 
> Should I reduce the check to \.L_\S+ instead? (please note "_"
> following ".L")

Use grep first.  That would still match several existing labels.

> Pardon me, I'm not good with assembly :/

Spending time reading docs can help with that.

Mark?  Can you please comment about the below?

I believe the test should be:

	if ($realfile =~ /\.S$/ &&
	    $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
		WARN(...);
	}

so that only this code currently matches:

$ git grep -P '^\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L' -- '*.S'
arch/x86/boot/compressed/head_32.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
arch/x86/boot/compressed/head_32.S:SYM_FUNC_END(.Lrelocated)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lrelocated)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lpaging_enabled)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lno_longmode)
arch/x86/boot/compressed/head_64.S:SYM_FUNC_END(.Lno_longmode)
arch/x86/boot/pmjump.S:SYM_FUNC_START_LOCAL_NOALIGN(.Lin_pm32)
arch/x86/boot/pmjump.S:SYM_FUNC_END(.Lin_pm32)
arch/x86/entry/entry_64.S:SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs)
arch/x86/entry/entry_64.S:SYM_CODE_END(.Lbad_gs)
arch/x86/lib/copy_user_64.S:SYM_CODE_START_LOCAL(.Lcopy_user_handle_tail)
arch/x86/lib/copy_user_64.S:SYM_CODE_END(.Lcopy_user_handle_tail)
arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_clac)
arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_clac)
arch/x86/lib/getuser.S:SYM_CODE_START_LOCAL(.Lbad_get_user_8_clac)
arch/x86/lib/getuser.S:SYM_CODE_END(.Lbad_get_user_8_clac)
arch/x86/lib/putuser.S:SYM_CODE_START_LOCAL(.Lbad_put_user_clac)
arch/x86/lib/putuser.S:SYM_CODE_END(.Lbad_put_user_clac)
arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_START_LOCAL(.Lwakeup_idt)
arch/x86/realmode/rm/wakeup_asm.S:SYM_DATA_END(.Lwakeup_idt)