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Subject: Re: [PATCH] perf: Support Python 3.8+ in Makefile
To:     Sam Lunt <samueljlunt@gmail.com>, <linux-kernel@vger.kernel.org>,
        <peterz@infradead.org>, <mingo@redhat.com>, <acme@kernel.org>
CC:     <mark.rutland@arm.com>, <alexander.shishkin@linux.intel.com>,
        <jolsa@redhat.com>, <namhyung@kernel.org>, <trivial@kernel.org>
References: <20200131181123.tmamivhq4b7uqasr@gmail.com>
From:   He Zhe <zhe.he@windriver.com>
Message-ID: <30752f2a-fe0b-4150-c32d-07690fb43b82@windriver.com>
Date:   Mon, 17 Feb 2020 10:23:54 +0800
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On 2/1/20 2:11 AM, Sam Lunt wrote:
> Python 3.8 changed the output of 'python-config --ldflags' to no longer
> include the '-lpythonX.Y' flag (this apparently fixed an issue loading
> modules with a statically linked Python executable).  The libpython
> feature check in linux/build/feature fails if the Python library is not
> included in FEATURE_CHECK_LDFLAGS-libpython variable.
>
> This adds a check in the Makefile to determine if PYTHON_CONFIG accepts
> the '--embed' flag and passes that flag alongside '--ldflags' if so.
>
> tools/perf is the only place the libpython feature check is used.
>
> Signed-off-by: Sam Lunt <samuel.j.lunt@gmail.com>
> ---
>  tools/perf/Makefile.config | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index c90f4146e5a2..ccf99351f058 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -228,8 +228,17 @@ strip-libs  = $(filter-out -l%,$(1))
>
>  PYTHON_CONFIG_SQ := $(call shell-sq,$(PYTHON_CONFIG))
>
> +# Python 3.8 changed the output of `python-config --ldflags` to not include the
> +# '-lpythonX.Y' flag unless '--embed' is also passed. The feature check for
> +# libpython fails if that flag is not included in LDFLAGS
> +ifeq ($(shell $(PYTHON_CONFIG_SQ) --ldflags --embed 2>&1 1>/dev/null; echo $$?), 0)
> +  PYTHON_CONFIG_LDFLAGS := --ldflags --embed
> +else
> +  PYTHON_CONFIG_LDFLAGS := --ldflags
> +endif
> +
>  ifdef PYTHON_CONFIG
> -  PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) --ldflags 2>/dev/null)
> +  PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) $(PYTHON_CONFIG_LDFLAGS) 2>/dev/null)

I met the same problem. Would the following change be more simple and clear?

-  PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) --ldflags 2>/dev/null)
+  PYTHON_EMBED_LDOPTS := $(shell $(PYTHON_CONFIG_SQ) --ldflags --embed 2>/dev/null || $(PYTHON_CONFIG_SQ) --ldflags 2>/dev/null)


Thanks,
Zhe


>    PYTHON_EMBED_LDFLAGS := $(call strip-libs,$(PYTHON_EMBED_LDOPTS))
>    PYTHON_EMBED_LIBADD := $(call grep-libs,$(PYTHON_EMBED_LDOPTS)) -lutil
>    PYTHON_EMBED_CCOPTS := $(shell $(PYTHON_CONFIG_SQ) --includes 2>/dev/null)
>
> base-commit: d5d359b0ac3ffc319ca93c46a4cfd87093759ad6