linux-kernel - Re: drivers/tty/serial/8250/8250_fintek.c:364: warning: 'probe_data' is used uninitialized in this function

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Date:   Wed, 09 Aug 2017 11:47:42 -0400
From:   Daniel Micay <danielmicay@...il.com>
To:     Arnd Bergmann <arnd@...db.de>,
        kbuild test robot <fengguang.wu@...el.com>
Cc:     kbuild-all@...org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: drivers/tty/serial/8250/8250_fintek.c:364: warning:
 'probe_data' is used uninitialized in this function

On Wed, 2017-08-09 at 17:32 +0200, Arnd Bergmann wrote:
> On Wed, Aug 9, 2017 at 5:07 PM, kbuild test robot
> <fengguang.wu@...el.com> wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin
> > ux.git master
> > head:   bfa738cf3dfae2111626650f86135f93c5ff0a22
> > commit: 6974f0c4555e285ab217cee58b6e874f776ff409
> > include/linux/string.h: add the option of fortified string.h
> > functions
> > date:   4 weeks ago
> > config: x86_64-randconfig-v0-08092220 (attached as .config)
> > compiler: gcc-4.4 (Debian 4.4.7-8) 4.4.7
> > reproduce:
> >         git checkout 6974f0c4555e285ab217cee58b6e874f776ff409
> >         # save the attached .config to linux build tree
> >         make ARCH=x86_64
> > 
> > All warnings (new ones prefixed by >>):
> > 
> >    In file included from include/linux/bitmap.h:8,
> >                     from include/linux/cpumask.h:11,
> >                     from arch/x86/include/asm/cpumask.h:4,
> >                     from arch/x86/include/asm/msr.h:10,
> >                     from arch/x86/include/asm/processor.h:20,
> >                     from arch/x86/include/asm/cpufeature.h:4,
> >                     from arch/x86/include/asm/thread_info.h:52,
> >                     from include/linux/thread_info.h:37,
> >                     from arch/x86/include/asm/preempt.h:6,
> >                     from include/linux/preempt.h:80,
> >                     from include/linux/spinlock.h:50,
> >                     from include/linux/seqlock.h:35,
> >                     from include/linux/time.h:5,
> >                     from include/linux/stat.h:18,
> >                     from include/linux/module.h:10,
> >                     from drivers/tty/serial/8250/8250_fintek.c:11:
> >    include/linux/string.h: In function 'strcpy':
> >    include/linux/string.h:209: warning: '______f' is static but
> > declared in inline function 'strcpy' which is not static
> >    include/linux/string.h:211: warning: '______f' is static but
> > declared in inline function 'strcpy' which is not static
> 
> 
> This clearly comes from __trace_if() when CONFIG_PROFILE_ALL_BRANCHES
> is enabled. I did not see the warning with gcc-7.1.1, and I guess this
> only
> happens on older compilers like the gcc-4.4 that was used here.
> 
> What is the reason for __FORTIFY_INLINE to be "extern __always_inline"
> rather than "static __always_inline"? If they cannot just be 'static',
> maybe
> this can be changed to depend on the compiler version.
> 
>        Arnd

It's important to get the semantics of using extern. It means if you do
something like &memcpy, it resolves to the address of the direct symbol
instead of generating a useless thunk for that object file. It might
also be required for Clang compatibility, I don't remember.

It could have a compiler version dependency or maybe one specifically
tied to old compiler && CONFIG_PROFILE_ALL_BRANCHES / other options that
conflict with it like that.