Date: Tue, 29 Mar 2011 02:59:47 -0500 From: Eitan Adler <lists@eitanadler.com> To: David Demelier <demelier.david@gmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: printf() leak? Message-ID: <AANLkTikyzSj8Nypo1ZDJhs97k-YZ65qda18vkSDNhnFz@mail.gmail.com> In-Reply-To: <4D918988.8090802@gmail.com> References: <4D918988.8090802@gmail.com>
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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.
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]
> =3D=3D67840=3D=3D =C2=A0 =C2=A0 =C2=A0 =C2=A0 suppressed: 4,096 bytes in =
1 blocks
Lets take a look at what valgrind says immediately after this:
=3D=3D14481=3D=3D For counts of detected and suppressed errors, rerun with:=
-v
One of the lines we get is
--14508-- used_suppression: 1 libc puts leak
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=3D168767 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 :-)
Thank you for trying to make FreeBSD better!
--=20
Eitan Adler
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