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hacking: Add some details to handle Valgrind output

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hacking: Add some text around the running of Valgrind along with example
output for "real" vs. "false positives".

cfg.mk: Add hacking.in.html to sc_prohibit_raw_allocation
This commit is contained in:
John Ferlan 2013-02-05 10:03:56 -05:00
parent 1d8b4f0592
commit a141a43e33
2 changed files with 94 additions and 4 deletions
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2
cfg.mk
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@ -823,7 +823,7 @@ exclude_file_name_regexp--sc_prohibit_nonreentrant = \
^((po|tests)/|docs/.*(py|html\.in)|run.in$$)
exclude_file_name_regexp--sc_prohibit_raw_allocation = \
^(src/util/viralloc\.[ch]|examples/.*|tests/securityselinuxhelper.c)$$
^(docs/hacking\.html\.in)|(src/util/viralloc\.[ch]|examples/.*|tests/securityselinuxhelper.c)$$
exclude_file_name_regexp--sc_prohibit_readlink = \
^src/(util/virutil|lxc/lxc_container)\.c$$

96
docs/hacking.html.in
View File

@ -109,8 +109,9 @@
make syntax-check
make -C tests valgrind
</pre>
<p>
The latter test checks for memory leaks.
<p><a href="http://valgrind.org/">Valgrind</a> is a test that checks
for memory management issues, such as leaks or use of uninitialized
variables.
</p>
<p>
@ -134,7 +135,96 @@
<p>There is also a <code>./run</code> script at the top level,
to make it easier to run programs that have not yet been
installed, as well as to wrap invocations of various tests
under gdb or valgrind.</p>
under gdb or Valgrind.
</p>
</li>
<li><p>The Valgrind test should produce similar output to
<code>make check</code>. If the output has traces within libvirt
API's, then investigation is required in order to determine the
cause of the issue. Output such as the following indicates some
sort of leak:
</p>
<pre>
==5414== 4 bytes in 1 blocks are definitely lost in loss record 3 of 89
==5414== at 0x4A0881C: malloc (vg_replace_malloc.c:270)
==5414== by 0x34DE0AAB85: xmlStrndup (in /usr/lib64/libxml2.so.2.7.8)
==5414== by 0x4CC97A6: virDomainVideoDefParseXML (domain_conf.c:7410)
==5414== by 0x4CD581D: virDomainDefParseXML (domain_conf.c:10188)
==5414== by 0x4CD8C73: virDomainDefParseNode (domain_conf.c:10640)
==5414== by 0x4CD8DDB: virDomainDefParse (domain_conf.c:10590)
==5414== by 0x41CB1D: testCompareXMLToArgvHelper (qemuxml2argvtest.c:100)
==5414== by 0x41E20F: virtTestRun (testutils.c:161)
==5414== by 0x41C7CB: mymain (qemuxml2argvtest.c:866)
==5414== by 0x41E84A: virtTestMain (testutils.c:723)
==5414== by 0x34D9021734: (below main) (in /usr/lib64/libc-2.15.so)
</pre>
<p>In this example, the <code>virDomainDefParseXML()</code> had
an error path where the <code>virDomainVideoDefPtr video</code>
pointer was not properly disposed. By simply adding a
<code>virDomainVideoDefFree(video);</code> in the error path,
the issue was resolved.
</p>
<p>Another common mistake is calling a printing function, such as
<code>VIR_DEBUG()</code> without initializing a variable to be
printed. The following example involved a call which could return
an error, but not set variables passed by reference to the call.
The solution was to initialize the variables prior to the call.
</p>
<pre>
==4749== Use of uninitialised value of size 8
==4749== at 0x34D904650B: _itoa_word (in /usr/lib64/libc-2.15.so)
==4749== by 0x34D9049118: vfprintf (in /usr/lib64/libc-2.15.so)
==4749== by 0x34D9108F60: __vasprintf_chk (in /usr/lib64/libc-2.15.so)
==4749== by 0x4CAEEF7: virVasprintf (stdio2.h:199)
==4749== by 0x4C8A55E: virLogVMessage (virlog.c:814)
==4749== by 0x4C8AA96: virLogMessage (virlog.c:751)
==4749== by 0x4DA0056: virNetTLSContextCheckCertKeyUsage (virnettlscontext.c:225)
==4749== by 0x4DA06DB: virNetTLSContextCheckCert (virnettlscontext.c:439)
==4749== by 0x4DA1620: virNetTLSContextNew (virnettlscontext.c:562)
==4749== by 0x4DA26FC: virNetTLSContextNewServer (virnettlscontext.c:927)
==4749== by 0x409C39: testTLSContextInit (virnettlscontexttest.c:467)
==4749== by 0x40AB8F: virtTestRun (testutils.c:161)
</pre>
<p>Valgrind will also find some false positives or code paths
which cannot be resolved by making changes to the libvirt code.
For these paths, it is possible to add a filter to avoid the
errors. For example:
</p>
<pre>
==4643== 7 bytes in 1 blocks are possibly lost in loss record 4 of 20
==4643== at 0x4A0881C: malloc (vg_replace_malloc.c:270)
==4643== by 0x34D90853F1: strdup (in /usr/lib64/libc-2.15.so)
==4643== by 0x34EEC2C08A: ??? (in /usr/lib64/libnl.so.1.1)
==4643== by 0x34EEC15B81: ??? (in /usr/lib64/libnl.so.1.1)
==4643== by 0x34D8C0EE15: call_init.part.0 (in /usr/lib64/ld-2.15.so)
==4643== by 0x34D8C0EECF: _dl_init (in /usr/lib64/ld-2.15.so)
==4643== by 0x34D8C01569: ??? (in /usr/lib64/ld-2.15.so)
</pre>
<p>In this instance, it is acceptible to modify the
<code>tests/.valgrind.supp</code> file in order to add a
suppression filter. The filter should be unique enough to
not suppress real leaks, but it should be generic enough to
cover multiple code paths. The format of the entry can be
found in the documentation found at the
<a href="http://valgrind.org/">Valgrind home page.</a>
The following trace was added to <code>tests/.valgrind.supp</code>
in order to suppress the warning:
</p>
<pre>
{
dlInitMemoryLeak1
Memcheck:Leak
fun:?alloc
...
fun:call_init.part.0
fun:_dl_init
...
obj:*/lib*/ld-2.*so*
}
</pre>
</li>
<li>Update tests and/or documentation, particularly if you are adding
a new feature or changing the output of a program.</li>