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SubjectRe: [FYI][PATCH 1/1] tools build: Remove needless libpython-version feature check that breaks test-all fast path
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On 30/11/2021 13:26, Arnaldo Carvalho de Melo wrote:
> Since 66dfdff03d196e51 ("perf tools: Add Python 3 support") we don't use
> the tools/build/feature/test-libpython-version.c version in any Makefile
> feature check:
>
> $ find tools/ -type f | xargs grep feature-libpython-version
> $
>
> The only place where this was used was removed in 66dfdff03d196e51:
>
> - ifneq ($(feature-libpython-version), 1)
> - $(warning Python 3 is not yet supported; please set)
> - $(warning PYTHON and/or PYTHON_CONFIG appropriately.)
> - $(warning If you also have Python 2 installed, then)
> - $(warning try something like:)
> - $(warning $(and ,))
> - $(warning $(and ,) make PYTHON=python2)
> - $(warning $(and ,))
> - $(warning Otherwise, disable Python support entirely:)
> - $(warning $(and ,))
> - $(warning $(and ,) make NO_LIBPYTHON=1)
> - $(warning $(and ,))
> - $(error $(and ,))
> - else
> - LDFLAGS += $(PYTHON_EMBED_LDFLAGS)
> - EXTLIBS += $(PYTHON_EMBED_LIBADD)
> - LANG_BINDINGS += $(obj-perf)python/perf.so
> - $(call detected,CONFIG_LIBPYTHON)
> - endif
>
> And nowadays we either build with PYTHON=python3 or just install the
> python3 devel packages and perf will build against it.

I just tried this and found a combo that doesn't work and fails with this
error (unrelated to this change):

Makefile.config:812: No 'python-config' tool was found: disables Python support - please install python-devel/python-dev

The combo is when the python2 runtime is installed, but the python3 devtools
are installed. I didn't realise this when I added the python 3 autodetection,
I only fixed the issue for a system that was solely python3.

Do you think I should fix this? Currently the workaround is PYTHON=python3,
maybe it's enough of an edge case that it's ok?


>
> But the leftover feature-libpython-version check made the fast path
> feature detection to break in all cases except when python2 devel files
> were installed:
>
> $ rpm -qa | grep python.*devel
> python3-devel-3.9.7-1.fc34.x86_64
> $ rm -rf /tmp/build/perf ; mkdir -p /tmp/build/perf ;
> $ make -C tools/perf O=/tmp/build/perf install-bin
> make: Entering directory '/var/home/acme/git/perf/tools/perf'
> BUILD: Doing 'make -j32' parallel build
> HOSTCC /tmp/build/perf/fixdep.o
> <SNIP>
> $ cat /tmp/build/perf/feature/test-all.make.output
> In file included from test-all.c:18:
> test-libpython-version.c:5:10: error: #error
> 5 | #error
> | ^~~~~
> $ ldd ~/bin/perf | grep python
> libpython3.9.so.1.0 => /lib64/libpython3.9.so.1.0 (0x00007fda6dbcf000)
> $
>
> As python3 is the norm these days, fix this by just removing the unused
> feature-libpython-version feature check, making the test-all fast path
> to work with the common case.
>
> With this:
>
> $ rm -rf /tmp/build/perf ; mkdir -p /tmp/build/perf ;
> $ make -C tools/perf O=/tmp/build/perf install-bin |& head
> make: Entering directory '/var/home/acme/git/perf/tools/perf'
> BUILD: Doing 'make -j32' parallel build
> HOSTCC /tmp/build/perf/fixdep.o
> HOSTLD /tmp/build/perf/fixdep-in.o
> LINK /tmp/build/perf/fixdep
>
> Auto-detecting system features:
> ... dwarf: [ on ]
> ... dwarf_getlocations: [ on ]
> ... glibc: [ on ]
> $ ldd ~/bin/perf | grep python
> libpython3.9.so.1.0 => /lib64/libpython3.9.so.1.0 (0x00007f58800b0000)
> $ cat /tmp/build/perf/feature/test-all.make.output
> $
>
> Fixes: 66dfdff03d196e51 ("perf tools: Add Python 3 support")
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Cc: Ian Rogers <irogers@google.com>
> Cc: Jaroslav Škarvada <jskarvad@redhat.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
> tools/build/Makefile.feature | 1 -
> tools/build/feature/Makefile | 4 ----
> tools/build/feature/test-all.c | 5 -----
> tools/build/feature/test-libpython-version.c | 11 -----------
> tools/perf/Makefile.config | 2 --
> 5 files changed, 23 deletions(-)
> delete mode 100644 tools/build/feature/test-libpython-version.c
>


Reviewed-by: James Clark <james.clark@arm.com>

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