{"id":1766,"date":"2012-12-23T08:50:54","date_gmt":"2012-12-23T08:50:54","guid":{"rendered":"https:\/\/lineo.es\/python-valgrind-extension-c\/"},"modified":"2026-04-01T07:17:16","modified_gmt":"2026-04-01T07:17:16","slug":"python-valgrind","status":"publish","type":"post","link":"https:\/\/lineo.es\/en\/python-valgrind\/","title":{"rendered":"Python: Running Valgrind on a C extension"},"content":{"rendered":"\t\t
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Python: Running Valgrind on a C extension<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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This is how I use\u00a0Valgrind<\/a>\u00a0to check for memory bugs in\u00a0pygit2<\/a>.<\/p>

Glibc with debug symbols<\/h4>

The first issue I run into is that Valgrind refused to work if\u00a0Glibc<\/a>\u00a0was not compiled with debug symbols.<\/p>

This is how I did in my\u00a0Gentoo<\/a>\u00a0notebook, I edited the \/etc\/portage\/make.conf file to enable the\u00a0splitdebug<\/i>\u00a0feature:<\/p>

\/etc\/portage\/make.conf\nFEATURES=\"${FEATURES} splitdebug compressdebug -nostrip\"<\/pre>
Then re-emerged the glibc:<\/p>
$ sudo emerge glibc<\/pre>
Then commented out the splitdebug feature to avoid emerging other packages with debug symbols (there is likely a better way to do this).<\/p>
Valgrind 3.7<\/h4>
The big problem is that running Valgrind with a Python C extension raises tons of false positives. There are a number of things you need to do to avoid all these false positives.<\/p>
The first one is to use latest version of Valgrind 3.7, because of some bug I forgot about present in version 3.6<\/p>
Python, compiling for a memory debugger<\/h4>
Now, you need to install a version of Python to be used with Valgrind:<\/p>
$ .\/configure --prefix=\/...\/Python-3.7.4-valgrind --<\/span>without<\/span>-<\/span>pymalloc <\/span>--<\/span>with<\/span>-<\/span>pydebug <\/span>--<\/span>with<\/span>-<\/span>valgrind<\/span><\/code> $ make $ make install<\/pre>
Install pytest and pygit2<\/h4>
$ curl https:\/\/bootstrap.pypa.io\/get-pip.py -o get-pip.py\n$ \/...\/Python-3.7.4-valgrind\/bin\/python3 get-pip.py\n$ \/...\/Python-3.7.4-valgrind\/bin\/pip install pytest\n[...]\n$ \/...\/Python-3.7.4-valgrind\/bin\/python3 setup.py install<\/pre>
The suppression file<\/h4>
Now you need to use the suppression file that you will find in the Python sources, at Misc\/valgrind-python.supp. This is how I run the unit tests in pygit2 to find issues:<\/p>
$ valgrind --trace-children=yes --suppressions=valgrind-python.supp \\\n    \/...\/Python-3.7.4-valgrind\/bin\/pytest<\/pre>
That\u2019s it.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"
This is how I use\u00a0Valgrind\u00a0to check for memory bugs in\u00a0pygit2. Glibc with debug symbols The first issue I run into is that Valgrind refused to work if\u00a0Glibc\u00a0was not compiled with debug symbols. This is how I did in my\u00a0Gentoo\u00a0notebook, I edited the \/etc\/portage\/make.conf file to enable the\u00a0splitdebug\u00a0feature: \/etc\/portage\/make.conf FEATURES=”${FEATURES} splitdebug compressdebug -nostrip” Then re-emerged the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"elementor_header_footer","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1766","post","type-post","status-publish","format-standard","hentry","category-sin-categoria"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/posts\/1766","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/comments?post=1766"}],"version-history":[{"count":5,"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/posts\/1766\/revisions"}],"predecessor-version":[{"id":2141,"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/posts\/1766\/revisions\/2141"}],"wp:attachment":[{"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/media?parent=1766"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/categories?post=1766"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lineo.es\/en\/wp-json\/wp\/v2\/tags?post=1766"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}