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

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Date:   Mon, 5 Feb 2018 22:48:36 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
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 5, 2018 at 10:39 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 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.

Right, got it now. So my patch is correct either way, just the description
could have been better.

       Arnd