From: Segher Boessenkool <segher@kernel.crashing.org>
To: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Cc: syzkaller@googlegroups.com, linuxppc-dev@lists.ozlabs.org,
dvyukov@google.com
Subject: Re: [PATCH 1/2] powerpc/64s: Work around spurious warning on old gccs with -fsanitize-coverage
Date: Thu, 7 Feb 2019 01:49:47 -0600 [thread overview]
Message-ID: <20190207074947.GT14180@gate.crashing.org> (raw)
In-Reply-To: <630e392b-e9a7-6b1e-e3d8-c5382f94e5d7@au1.ibm.com>
On Thu, Feb 07, 2019 at 05:59:48PM +1100, Andrew Donnellan wrote:
> On 7/2/19 5:37 pm, Segher Boessenkool wrote:
> >On Thu, Feb 07, 2019 at 04:33:23PM +1100, Andrew Donnellan wrote:
> >>Some older gccs (<GCC 7), when invoked with -fsanitize-coverage=trace-pc,
> >>cause a spurious uninitialised variable warning in dt_cpu_ftrs.c:
> >>
> >> arch/powerpc/kernel/dt_cpu_ftrs.c: In function
> >> ‘cpufeatures_process_feature’:
> >> arch/powerpc/kernel/dt_cpu_ftrs.c:686:7: warning: ‘m’ may be used
> >> uninitialized in this function [-Wmaybe-uninitialized]
> >> if (m->cpu_ftr_bit_mask)
> >
> >It seems to me the warning is correct? If enable_unknown is false and no
> >cpu_feature is found, it will in
> >
> > if (m->cpu_ftr_bit_mask)
> > cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
> >
> >enable random features (whatever was last in the table), or indeed access
> >via NULL if the table is length 0? So maybe this should be
> >
> > if (known && m->cpu_ftr_bit_mask)
> > cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
> >
> >instead? (The code would be much clearer if all the known vs. !known
> >codepath was fully separated here).
>
> The table is never length 0, it's a statically defined array.
Sure, and presumably that is why newer GCC doesn't warn. But what about
the other point? Is this code ever correct? Enabling random features
(in cur_cpu_spec->cpu_features) when the name isn't found seems wrong.
Segher
next prev parent reply other threads:[~2019-02-07 7:51 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-07 5:33 [PATCH 1/2] powerpc/64s: Work around spurious warning on old gccs with -fsanitize-coverage Andrew Donnellan
2019-02-07 5:33 ` [PATCH 2/2] powerpc: Enable kcov Andrew Donnellan
2019-02-07 6:37 ` [PATCH 1/2] powerpc/64s: Work around spurious warning on old gccs with -fsanitize-coverage Segher Boessenkool
2019-02-07 6:59 ` Andrew Donnellan
2019-02-07 7:49 ` Segher Boessenkool [this message]
2019-02-08 0:34 ` Andrew Donnellan
2019-02-08 3:02 ` Michael Ellerman
2019-02-08 3:11 ` Andrew Donnellan
2019-02-08 15:41 ` Segher Boessenkool
2019-02-10 5:14 ` Andrew Donnellan
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