https://bugs.kde.org/show_bug.cgi?id=421931
Bug ID: 421931
Summary: Enhance valgrind to supress unfreed stderr.
Product: valgrind
Version: 3.15 SVN
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: wishlist
Priority: NOR
Component: general
Assignee: jsew...@acm.org
Reporter: car...@redhat.com
Target Milestone: ---
SUMMARY
In glibc the __libc_freeres() function which handles freeing all resources for
allocation trackers, will not free unbuffered streams. We don't free unbuffered
streams because users may expect to continue using them throughout all of the
process shutdown steps. As such, when you use stderr in your program it creates
a leak that can be seen by users.
STEPS TO REPRODUCE
1. Create leak.c
#include <stdio.h>
#include <wchar.h>
int main ( void )
{
fwprintf ( stderr , L"valgrind error\n" ) ;
return 0 ;
}
2. Compile.
3. Run with valgrind --leak-check=full --show-leak-kinds=all
OBSERVED RESULT
valgrind --leak-check=full --show-leak-kinds=all ./leak
==258071== Memcheck, a memory error detector
==258071== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==258071== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==258071== Command: ./leak
==258071==
valgrind error
==258071==
==258071== HEAP SUMMARY:
==258071== in use at exit: 5,120 bytes in 2 blocks
==258071== total heap usage: 2 allocs, 0 frees, 5,120 bytes allocated
==258071==
==258071== 1,024 bytes in 1 blocks are still reachable in loss record 1 of 2
==258071== at 0x483A809: malloc (vg_replace_malloc.c:309)
==258071== by 0x4907FC3: _IO_file_doallocate (filedoalloc.c:101)
==258071== by 0x490940C: _IO_wfile_doallocate (wfiledoalloc.c:70)
==258071== by 0x4916D1F: _IO_doallocbuf (genops.c:347)
==258071== by 0x4916D1F: _IO_doallocbuf (genops.c:342)
==258071== by 0x490FBBF: _IO_wfile_overflow (wfileops.c:429)
==258071== by 0x490D22E: __woverflow (wgenops.c:217)
==258071== by 0x490D22E: _IO_wdefault_xsputn (wgenops.c:317)
==258071== by 0x490D22E: _IO_wdefault_xsputn (wgenops.c:284)
==258071== by 0x490FDF0: _IO_wfile_xsputn (wfileops.c:1011)
==258071== by 0x490FDF0: _IO_wfile_xsputn (wfileops.c:957)
==258071== by 0x4906BC1: buffered_vfprintf (vfprintf-internal.c:2388)
==258071== by 0x4903E4B: __vfwprintf_internal (vfprintf-internal.c:1346)
==258071== by 0x490C439: fwprintf (fwprintf.c:33)
==258071== by 0x401152: main (leak.c:9)
==258071==
==258071== 4,096 bytes in 1 blocks are still reachable in loss record 2 of 2
==258071== at 0x483A809: malloc (vg_replace_malloc.c:309)
==258071== by 0x49093DC: _IO_wfile_doallocate (wfiledoalloc.c:79)
==258071== by 0x4916D1F: _IO_doallocbuf (genops.c:347)
==258071== by 0x4916D1F: _IO_doallocbuf (genops.c:342)
==258071== by 0x490FBBF: _IO_wfile_overflow (wfileops.c:429)
==258071== by 0x490D22E: __woverflow (wgenops.c:217)
==258071== by 0x490D22E: _IO_wdefault_xsputn (wgenops.c:317)
==258071== by 0x490D22E: _IO_wdefault_xsputn (wgenops.c:284)
==258071== by 0x490FDF0: _IO_wfile_xsputn (wfileops.c:1011)
==258071== by 0x490FDF0: _IO_wfile_xsputn (wfileops.c:957)
==258071== by 0x4906BC1: buffered_vfprintf (vfprintf-internal.c:2388)
==258071== by 0x4903E4B: __vfwprintf_internal (vfprintf-internal.c:1346)
==258071== by 0x490C439: fwprintf (fwprintf.c:33)
==258071== by 0x401152: main (leak.c:9)
==258071==
==258071== LEAK SUMMARY:
==258071== definitely lost: 0 bytes in 0 blocks
==258071== indirectly lost: 0 bytes in 0 blocks
==258071== possibly lost: 0 bytes in 0 blocks
==258071== still reachable: 5,120 bytes in 2 blocks
==258071== suppressed: 0 bytes in 0 blocks
==258071==
==258071== For lists of detected and suppressed errors, rerun with: -s
==258071== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
EXPECTED RESULT
- Given that stderr might be used a lot by developers we could enhance valgrind
to try supress unfreed unbuffered stderr at process exit.
- For a high QoI we would supress all unfreed unbuffered streams since the
expectation, at least in glibc, is that none of these are freed with
__libc_freeres() because the could continue to be used during process shutdown.
SOFTWARE/OS VERSIONS
Fedora 32:
valgrind-3.15.0-20.fc32.x86_64
ADDITIONAL INFORMATION
N/A
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