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

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Message-ID: <CAFP8O3+g3KDe1eepGiCXqwMU6K2ve_2ai69WRBCORrr5UAJT+A@mail.gmail.com>
Date:   Fri, 22 Jan 2021 12:36:03 -0800
From:   Fāng-ruì Sòng <maskray@...gle.com>
To:     Aditya <yashsri421@...il.com>
Cc:     Joe Perches <joe@...ches.com>, LKML <linux-kernel@...r.kernel.org>,
        lukas.bulwahn@...il.com, dwaipayanray1@...il.com,
        Mark Brown <broonie@...nel.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] checkpatch: add warning for avoiding .L prefix symbols in
 assembly files

On Fri, Jan 22, 2021 at 12:13 PM Aditya <yashsri421@...il.com> wrote:
>
> On 23/1/21 12:40 am, Joe Perches wrote:
> > On Fri, 2021-01-22 at 18:48 +0530, Aditya wrote:
> >> On 21/1/21 12:13 am, Joe Perches wrote:
> >>> I believe the test should be:
> >>>
> >>>     if ($realfile =~ /\.S$/ &&
> >>>         $line =~ /^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) {
> >>
> >> Joe, with this regex, we won't be able to match
> >> "jmp  .L_restore
> >> SYM_FUNC_END(\name)"
> >
> > I think that's not an issue.
> >
> >> which was replaced in this patch in the discussion:
> >> https://groups.google.com/g/clang-built-linux/c/-drkmLgu-cU/m/phKe-Tb6CgAJ
> >>
> >> Here, "jmp  .L_restore" was also replaced to fix the error.
> >
> > Notice that this line was also replaced in the same patch:
> >
> >  #ifdef CONFIG_PREEMPTION
> > -SYM_CODE_START_LOCAL_NOALIGN(.L_restore)
> > +SYM_CODE_START_LOCAL_NOALIGN(__thunk_restore)
> >
> >
> >> However, if this
> >> regex(/^\+\s*SYM_[A-Z]+_(?:START|END)(?:_[A-Z_]+)?\s*\(\s*\.L/) is
> >> correct, maybe we don't need to check for $file as we are now checking
> >> for just one line.
> >>
> >> What do you think?
> >
> > The test I wrote was complete, did not use $file and emits a
> > warning on the use of CODE_SYM_START_LOCAL_NOALIGN(.L_restore)
> >
> > I think it's sufficient.
> >
>
> Okay, Thanks.. I will send the modified patch :)
>
> Thanks
> Aditya

I am slightly concerned with the direction here.   jmp .Lsym is fine
and is probably preferable in cases where you absolutely want to emit
a local symbol.
(there is a related -z unique-symbol GNU ld+FGKASLR thing I shall
analyze in my spare time)

If the problem is just that STT_SECTION symbols are missing, can
objtool do something to conceptually synthesize them?