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Re: Running bash under valgrind gives "invalid free()"


From: Chet Ramey
Subject: Re: Running bash under valgrind gives "invalid free()"
Date: Thu, 13 Apr 2017 11:27:48 -0400
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On 4/13/17 11:18 AM, Reuben Thomas wrote:
> On 13 April 2017 at 16:11, Chet Ramey <address@hidden
> <mailto:address@hidden>> wrote:
> 
> 
>     I see no reason why, since all of these things are defined in the same
>     file and are statically linked, `free' would resolve to the glibc free
>     when malloc resolves to the bash malloc.
> 
> 
> So this is the real problem?​

If it is, it's a valgrind artifact.  Contrary to Julian's (?) assumption,
free() resolves to the bash free implementation when compiled normally. I
tested this on a Fedora 25 VM I was using for something else.  Putting a
breakpoint in xfree, running bash -c '', and stepping through it ends up
in the free() defined in lib/malloc/malloc.c.

>  
> ​Do you have any suggestions for how I might investigate this?​

Personally, I think the problem is that valgrind makes invalid assumptions:
that interposing malloc/realloc/free is sufficient.  I showed it isn't.

You can try building without the bash malloc, but that's kind of a drastic
solution to just get rid of a valgrind false positive.

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/



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