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


From: Reuben Thomas
Subject: Re: Running bash under valgrind gives "invalid free()"
Date: Thu, 13 Apr 2017 15:33:05 +0100

On 12 April 2017 at 15:49, Chet Ramey <address@hidden> wrote:

It's a false positive, or a bug in valgrind. I took a quick look.  There's
one place in this code path where free() gets called.

​Julian Seward (valgrind author) pointed out:​

"
​…​
what you report is symptomatic of bash
​ ​
using its own malloc to allocate a block but the system free to release
​ ​
it.  Could that be the case?
​"

I had a look. Certainly at xmalloc.c:148 where free is called by xfree from the cleanup function called at unwind_prot.c:333, gdb reports:

p free
$7 = {void (void *)} 0x7ffff7df0d80 <free>

This is glibc free.

If I put a breakpoint on xmalloc and rerun, it is not hit.

If I put a breakpoint on shell.c:1399, and trace into savestring, I find it is running sh_xmalloc.

So it seems that the malloc and free calls are mismatched.


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