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

From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Nicolas Pitre <nico@linaro.org>, Vlastimil Babka <vbabka@suse.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	bpetkov@suse.de,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andi Kleen <ak@linux.intel.com>,
	linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/dumpstack: Avoid uninitlized variable
Date: Mon, 5 Feb 2018 15:39:11 -0600	[thread overview]
Message-ID: <20180205213911.2auyud6a3k2ng7jx@treble> (raw)
In-Reply-To: <CAK8P3a3MMwRQ00YxuPhEmNzqiMn4+VX48b82831i+kCqruCMfQ@mail.gmail.com>

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@zytor.com> wrote:
> > Commit-ID:  ebfc15019cfa72496c674ffcb0b8ef10790dcddc
> > Gitweb:     https://git.kernel.org/tip/ebfc15019cfa72496c674ffcb0b8ef10790dcddc
> > Author:     Arnd Bergmann <arnd@arndb.de>
> > AuthorDate: Fri, 2 Feb 2018 15:56:17 +0100
> > Committer:  Thomas Gleixner <tglx@linutronix.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