linux-kernel - Re: [tip:x86/urgent] x86/dumpstack: Avoid uninitlized variable

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Date:   Mon, 5 Feb 2018 15:39:11 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Pitre <nico@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, bpetkov@...e.de,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86/dumpstack: Avoid uninitlized variable

On Mon, Feb 05, 2018 at 10:21:06PM +0100, Arnd Bergmann wrote:
> On Fri, Feb 2, 2018 at 11:36 PM, tip-bot for Arnd Bergmann
> <tipbot@...or.com> wrote:
> > Commit-ID:  ebfc15019cfa72496c674ffcb0b8ef10790dcddc
> > Gitweb:     https://git.kernel.org/tip/ebfc15019cfa72496c674ffcb0b8ef10790dcddc
> > Author:     Arnd Bergmann <arnd@...db.de>
> > AuthorDate: Fri, 2 Feb 2018 15:56:17 +0100
> > Committer:  Thomas Gleixner <tglx@...utronix.de>
> > CommitDate: Fri, 2 Feb 2018 23:33:50 +0100
> >
> > x86/dumpstack: Avoid uninitlized variable
> >
> > In some configurations, 'partial' does not get initialized, as shown by
> > this gcc-8 warning:
> >
> > arch/x86/kernel/dumpstack.c: In function 'show_trace_log_lvl':
> > arch/x86/kernel/dumpstack.c:156:4: error: 'partial' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >     show_regs_if_on_stack(&stack_info, regs, partial);
> >     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > This initializes it to false, to get the previous behavior in this case.
> >
> > Fixes: a9cdbe72c4e8 ("x86/dumpstack: Fix partial register dumps")
> 
> 
> I just noticed my annotation got lost when I sent the patch. I originally
> meant to ask Josh to double-check whether it should be 'false' or 'true'
> here, or if we maybe need a larger change.
> 
> Josh, could you take a look? Unfortunately I did not really understand
> your original commit, so I don't know what the safe choice is here
> in those cases in which 'partial' is uninitialized.

I think it doesn't matter, it seems to be a false positive warning.

The 'partial' variable is only used when 'regs' is non-NULL, and 'regs'
is only set in unwind_get_entry_regs() after 'partial' gets initialized.

-- 
Josh