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Re: [PATCH] fatal-signal: silence coverity warning

From: Pádraig Brady
Subject: Re: [PATCH] fatal-signal: silence coverity warning
Date: Fri, 29 Apr 2011 22:15:42 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100227 Thunderbird/3.0.3

On 29/04/11 22:00, Jim Meyering wrote:
> Eric Blake wrote:
>> On a glibc system, Coverity gives this warning:
>> Error: UNINIT:
>> m4-1.4.16/lib/fatal-signal.c:183: var_decl: Declaring variable "action" 
>> without initializer.
>> m4-1.4.16/lib/fatal-signal.c:198: uninit_use_in_call: Using uninitialized 
>> value "action": field "action".sa_restorer is uninitialized when calling 
>> "sigaction".
>> For glibc, the warning is spurious (the sa_restorer field is
>> silently overwritten inside the sigaction() implementation, so
>> it doesn't matter what the user assigns there, and leaving it
>> unitialized in the user is actually slightly more efficient).
>> But it could very well be a valid bug report for other platforms,
>> since POSIX allows other extension fields in struct sigaction;
>> always setting all extension fields to 0 (via memset) will
>> guarantee that those extension fields can't have arbitrary
>> behavior due to being uninitialized.
>> * lib/fatal-signal.c (install_handlers): Clear undocumented fields.
>> Signed-off-by: Eric Blake <address@hidden>
>> ---
>> I'm not sure whether we should apply this patch.  On the one
>> hand, you can argue (as I did in the commit message) that
>> uninitialized hidden members can be dangerous.  On the other
>> hand, you can argue that if you stick to just the POSIX-defined
>> sa_flags values, then you can't trigger any extensions that
>> would care about the contents of extension fields in the
>> first palce.
>> Thoughts on whether I should apply or ditch this patch?
> ...
>> diff --git a/lib/fatal-signal.c b/lib/fatal-signal.c
>> index aca9027..80ffda5 100644
>> --- a/lib/fatal-signal.c
>> +++ b/lib/fatal-signal.c
>> @@ -182,6 +182,7 @@ install_handlers ()
>>    size_t i;
>>    struct sigaction action;
>> +  memset (&action, 0, sizeof action);
>>    action.sa_handler = &fatal_signal_handler;
>>    /* If we get a fatal signal while executing fatal_signal_handler, enter
>>       fatal_signal_handler recursively, since it is reentrant.  Hence no
> I think the case for clearing the bits is a little
> stronger than the one for leaving them uninitialized, and would
> be even more in favor, it if only this initialization were portable:
>   struct sigaction action = {0,};
> Now that gcc is fixed,
> maybe we should use something like DECLARE_ZEROED_AUTO,
>   http://thread.gmane.org/gmane.comp.gnu.coreutils.general/1124/focus=1131
> here in gnulib, too.

Well {0,} is already used in gnulib.

I'm going to change manywarnings.m4 so that
-Wno-missing-field-initializers is added if needed.

Then we don't need to worry about any of this.


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