linux-kernel - Re: [PATCH] tools: perf: Avoid error message when building with no python installed

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Date:	Tue, 28 Jul 2015 13:49:12 +0100
From:	Pawel Moll <pawel.moll@....com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tools: perf: Avoid error message when building with no
 python installed

On Mon, 2015-07-27 at 19:36 +0100, Jiri Olsa wrote:
> > @@ -150,7 +150,7 @@ ifndef NO_LIBPYTHON
> >    PYTHON2 := $(if $(call get-executable,python2),python2,python)
> >    override PYTHON := $(call get-executable-or-default,PYTHON,$(PYTHON2))
> >    PYTHON2_CONFIG := \
> > -    $(if $(call get-executable,$(PYTHON)-config),$(PYTHON)-config,python-config)
> > +    $(if $(PYTHON),$(if $(call get-executable,$(PYTHON)-config),$(PYTHON)-config,python-config))
> >    override PYTHON_CONFIG := \
> >      $(call get-executable-or-default,PYTHON_CONFIG,$(PYTHON2_CONFIG))
> 
> haven't tried, but seems like we want to add also the else part
> to get default into PYTHON_CONFIG?
> -    $(if $(PYTHON),$(if $(call get-executable,$(PYTHON)-config),$(PYTHON)-config,python-config))
> +    $(if $(PYTHON),$(if $(call get-executable,$(PYTHON)-config),$(PYTHON)-config,python-config),python-config)

It's not strictly necessary, because the issue here is just executing
"command -v -c" (followed by "onfig" :-), but of course it will still
work.

> it fails anyway later either way, but seems like the 'python-config'
> was the default case that was meant to fail later

Well, yes, I had the same impression. But at the same time
get-executable-or-default is constructed in such a way that either of
the variants must be a real executable:

--8<-----------
# get-supplied-or-default-executable
#
# Usage: absolute-executable-path-or-empty = $(call get-executable-or-default,variable,default)
#
define get-executable-or-default
$(if $($(1)),$(call _ge_attempt,$($(1)),$(1)),$(call _ge_attempt,$(2)))
endef
_ge_attempt = $(if $(get-executable),$(get-executable),$(call _gea_err,$(2)))
_gea_err  = $(if $(1),$(error Please set '$(1)' appropriately))
--8<-----------

See? Both alternatives in the $(if $($(1)) monster do _ge_attempt... So
one could say that the change may rather look like this (untested):

--8<-----------
diff --git a/tools/perf/config/utilities.mak
b/tools/perf/config/utilities.mak
index 0ebef09..78135dc 100644
--- a/tools/perf/config/utilities.mak
+++ b/tools/perf/config/utilities.mak
@@ -173,7 +173,7 @@ _ge-abspath = $(if $(is-executable),$(1))
 # Usage: absolute-executable-path-or-empty = $(call
get-executable-or-default,variable,default)
 #
 define get-executable-or-default
-$(if $($(1)),$(call _ge_attempt,$($(1)),$(1)),$(call _ge_attempt,$(2)))
+$(if $($(1)),$(call _ge_attempt,$($(1)),$(1)),$(2))
 endef
 _ge_attempt = $(if $(get-executable),$(get-executable),$(call _gea_err,
$(2)))
 _gea_err  = $(if $(1),$(error Please set '$(1)' appropriately))
--8<-----------

Pawel

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