Re: [PATCH] perf build: Do not duplicate CFLAGS in Python extension builds

[James Clark <james.clark@linaro.org>]

On 10/06/2026 12:23 pm, Jens Remus wrote:
> setuptools already uses CFLAGS.  Passing CFLAGS with additional flags as
> extra compile arguments causes CFLAGS to effectively get passed twice:
> 
> $ make -C tools/perf V=1 JOBS=1
> ...
> building 'perf' extension
> gcc [CFLAGS] -fPIC -Iutil/include -I/usr/include/python3.14 \
>    -c /root/linux/tools/perf/util/python.c \
>    -o python_ext_build/tmp/root/linux/tools/perf/util/python.o \
>    [CFLAGS] \
>    -fno-strict-aliasing -Wno-write-strings -Wno-unused-parameter \
>    -Wno-redundant-decls -Wno-cast-function-type \
>    -Wno-declaration-after-statement
> 
> Signed-off-by: Jens Remus <jremus@linux.ibm.com>

Reviewed-by: James Clark <james.clark@linaro.org>

> ---
> 
> Notes (jremus):
>      This patch applies on top of the perf-tools-next tree:
>      
>        git://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git  master
>      
>      Note that my "[PATCH v2] perf build: Respect V=1 for Python extension
>      builds" [1] needs to be applied to actually observe the Python extension
>      build command and output with V=1.
>      
>      [1]: https://lore.kernel.org/all/20260608160613.3153795-1-jremus@linux.ibm.com/
> 
>   tools/perf/util/setup.py | 13 ++++++-------
>   1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/perf/util/setup.py b/tools/perf/util/setup.py
> index b65b1792ca05..a0ce76624a23 100644
> --- a/tools/perf/util/setup.py
> +++ b/tools/perf/util/setup.py
> @@ -74,18 +74,17 @@ class install_lib(_install_lib):
>           self.build_dir = build_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', '-Wno-redundant-decls' ]
> +extra_cflags = ['-fno-strict-aliasing', '-Wno-write-strings', '-Wno-unused-parameter', '-Wno-redundant-decls' ]
>   if cc_is_clang:
> -    cflags += ["-Wno-unused-command-line-argument" ]
> +    extra_cflags += ["-Wno-unused-command-line-argument" ]
>       if clang_has_option("-Wno-cast-function-type-mismatch"):
> -        cflags += ["-Wno-cast-function-type-mismatch" ]
> +        extra_cflags += ["-Wno-cast-function-type-mismatch" ]
>   else:
> -    cflags += ['-Wno-cast-function-type' ]
> +    extra_cflags += ['-Wno-cast-function-type' ]
>   
>   # The python headers have mixed code with declarations (decls after asserts, for instance)
> -cflags += [ "-Wno-declaration-after-statement" ]
> +extra_cflags += [ "-Wno-declaration-after-statement" ]
>   
>   src_perf  = f'{srctree}/tools/perf'
>   build_lib = getenv('PYTHON_EXTBUILD_LIB')
> @@ -94,7 +93,7 @@ build_tmp = getenv('PYTHON_EXTBUILD_TMP')
>   perf = Extension('perf',
>                    sources = [ src_perf + '/util/python.c' ],
>   		         include_dirs = ['util/include'],
> -		         extra_compile_args = cflags,
> +		         extra_compile_args = extra_cflags,
>                    )
>   
>   setup(name='perf',