Date: Tue, 29 Mar 2011 10:08:33 +0200 From: David Demelier <demelier.david@gmail.com> To: Eitan Adler <lists@eitanadler.com> Cc: freebsd-questions@freebsd.org Subject: Re: printf() leak? Message-ID: <4D919381.70109@gmail.com> In-Reply-To: <AANLkTikyzSj8Nypo1ZDJhs97k-YZ65qda18vkSDNhnFz@mail.gmail.com> References: <4D918988.8090802@gmail.com> <AANLkTikyzSj8Nypo1ZDJhs97k-YZ65qda18vkSDNhnFz@mail.gmail.com>
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On 29/03/2011 09:59, Eitan Adler wrote:
> Hi David,
>
>> It seems printf() always alloc something and does not free it:
>
> What compiler and what optimizations? Most compilers will optimize a
> printf without any special formatting into a puts call instead of a
> printf call.
I was using clang / gcc without any optimisations.
> For example clang -O3 -fomit-frame-pointer (which I use for clarity
> here) outputs this code:
>
> .file "leak.c"
> ...
> main: # @main
> # BB#0: # %entry
> subl $12, %esp
> movl $str, (%esp)
> calll puts
> xorl %eax, %eax
> addl $12, %esp
> ret
> .Ltmp0:
> ...
> str:
> .asciz "Hi"
> .size str, 3
> ...
>
> [snip]
>> ==67840== suppressed: 4,096 bytes in 1 blocks
>
> Lets take a look at what valgrind says immediately after this:
> ==14481== For counts of detected and suppressed errors, rerun with: -v
>
> One of the lines we get is
> --14508-- used_suppression: 1 libc puts leak
>
I didn't see this one, thanks!
> Which means it is a known issue and has been specially marked as to
> avoid being reported by valgrind.
>
> Lets take a look to see where this suppression happens: in
> /usr/local/lib/valgrind/default.supp we find
> {
> libc puts leak
> Memcheck:Leak
> fun:malloc
> obj:/lib/libc.so.7
> obj:/lib/libc.so.7
> obj:/lib/libc.so.7
> fun:puts
> fun:main
> }
>
> After some investigation I was able to find the following commit:
> http://p4db.freebsd.org/chv.cgi?CH=168767 which shows when this
> suppression was added and by whom.
>
> I trust that if you are interested in the details of why this leak is
> detected you have the skills to follow up on this by yourself :-)
>
Thanks a lot for the details.
> Thank you for trying to make FreeBSD better!
>
>
:-)
--
David Demelier
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