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From: "Zdenek Sojka" <zsojka@seznam.cz>
To: "Jeff Law" <jeffreyalaw@gmail.com>
Cc: "Paul Floyd" <paulf@free.fr>,
	<gcc@gcc.gnu.org>
Subject: Re: distinguishing gcc compilation valgrind false positives
Date: Wed, 24 Nov 2021 20:41:08 +0100 (CET)
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Hello Jeff,

---------- P=C5=AFvodn=C3=AD e-mail ----------
Od: Jeff Law via Gcc <gcc@gcc.gnu.org>
Komu: Paul Floyd <paulf@free.fr>, gcc@gcc.gnu.org
Datum: 24. 11. 2021 20:33:02
P=C5=99edm=C4=9Bt: Re: distinguishing gcc compilation valgrind false posit=
ives 
" 

On 11/24/2021 12:15 PM, Paul Floyd via Gcc wrote: 
> 
> On 24/11/2021 20:05, Zdenek Sojka via Gcc wrote: 
>> Hello, 
>> 
>> from time to time, I come upon a testcase that failed during the 
>> automated 
>> runs, but passes during reduction; there are valgrind warnings present,=
 
>> however. How do I distinguish what warnings are valid and which are 
>> false 
>> positives? Is there any way gcc could prevent generating the false 
>> positives? 
> 
> 
> What makes you think that any are false positives? 
> 
> Memcheck generally has a low false positive rate (though I am little 
> biased). 
> 
> You need to read the source and decide based on that. 
Agreed.=C2=A0 Work from the assumption it's a real GCC issue until proven =

otherwise. 

I believe GCC has annotations to help valgrind that are turned on by a 
magic configuration option as well. 
"



I have gcc configured with --enable-valgrind-annotations , if that is the =

one you are talking about?


=C2=A0
"
Finally, there is an issue with sparsesets that will trigger a warning 
from valgrind.=C2=A0 Those are the only ones I would consistently ignore f=
rom 
GCC. 

Jeff "






Yes I remember those - but it would be nice to get rid of them anyway, at =

least to simplify testcase reduction by having no valgrind warning on a =

clean build.




I could also use a valgrind suppression file; this is also part of my 
question, if there is one readily available




Thanks,
Zdenek




=C2=A0
"
"