[PATCH 3.16 366/366] perf tools: Fix python extension build for gcc 8

Ben Hutchings
2018-11-11T20:32:32Z

From: Jiri Olsa <jolsa@kernel.org>

commit b7a313d84e853049062011d78cb04b6decd12f5c upstream.

The gcc 8 compiler won't compile the python extension code with the
following errors (one example):

python.c:830:15: error: cast between incompatible function types from \
‘PyObject * (*)(struct pyrf_evsel *, PyObject *, PyObject *)’ \
uct _object * (*)(struct pyrf_evsel *, struct _object *, struct _object *)’} to \
‘PyObject * (*)(PyObject *, PyObject *)’ {aka ‘struct _object * (*)(struct _objeuct \
_object *)’} [-Werror=cast-function-type]
.ml_meth = (PyCFunction)pyrf_evsel__open,

The problem with the PyMethodDef::ml_meth callback is that its type is
determined based on the PyMethodDef::ml_flags value, which we set as
METH_VARARGS | METH_KEYWORDS.

That indicates that the callback is expecting an extra PyObject* arg, and is
actually PyCFunctionWithKeywords type, but the base PyMethodDef::ml_meth type
stays PyCFunction.

Previous gccs did not find this, gcc8 now does. Fixing this by silencing this
warning for python.c build.

Commiter notes:

Do not do that for CC=clang, as it breaks the build in some clang
versions, like the ones in fedora up to fedora27:

fedora:25:error: unknown warning option '-Wno-cast-function-type'; did you mean '-Wno-bad-function-cast'? [-Werror,-Wunknown-warning-option]
fedora:26:error: unknown warning option '-Wno-cast-function-type'; did you mean '-Wno-bad-function-cast'? [-Werror,-Wunknown-warning-option]
fedora:27:error: unknown warning option '-Wno-cast-function-type'; did you mean '-Wno-bad-function-cast'? [-Werror,-Wunknown-warning-option]
#

those have:

clang version 3.9.1 (tags/RELEASE_391/final)

The one in rawhide accepts that:

clang version 6.0.0 (tags/RELEASE_600/final)

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Link: http://lkml.kernel.org/r/20180319082902.4518-2-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
tools/perf/util/setup.py | 2 ++
1 file changed, 2 insertions(+)

--- a/tools/perf/util/setup.py
+++ b/tools/perf/util/setup.py
@@ -21,6 +21,7 @@ class install_lib(_install_lib):
cflags = getenv('CFLAGS', '').split()
# switch off several checks (need to be at the end of cflags list)
cflags += ['-fno-strict-aliasing', '-Wno-write-strings', '-Wno-unused-parameter' ]
+cflags += ['-Wno-cast-function-type' ]

build_lib = getenv('PYTHON_EXTBUILD_LIB')
build_tmp = getenv('PYTHON_EXTBUILD_TMP')