[PATCH 1/1] perf tools: Use Python devtools for version autodetection rather than runtime

[James Clark <james.clark@arm.com>]

This fixes the issue where the build will fail if only the Python2
runtime is installed but the Python3 devtools are installed. Currently
the workaround is 'make PYTHON=python3'.

Fix it by autodetecting Python based on whether python[x]-config exists
rather than just python[x] because both are needed for the build. Then
-config is stripped to find the Python runtime.

Testing
=======

 * Auto detect links with Python3 when the v3 devtools are installed
   and only Python 2 runtime is installed
 * Auto detect links with Python2 when both devtools are installed
 * Sensible warning is printed if no Python devtools are installed
 * 'make PYTHON=x' still automatically sets PYTHON_CONFIG=x-config
 * 'make PYTHON=x' fails if x-config doesn't exist
 * 'make PYTHON=python3' overrides Python2 devtools
 * 'make PYTHON=python2' overrides Python3 devtools
 * 'make PYTHON_CONFIG=x-config' works
 * 'make PYTHON=x PYTHON_CONFIG=x' works
 * 'make PYTHON=missing' reports an error
 * 'make PYTHON_CONFIG=missing' reports an error

Fixes: 79373082fa9d ("perf python: Autodetect python3 binary")
Signed-off-by: James Clark <james.clark@arm.com>
---
 tools/perf/Makefile.config | 39 ++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 96ad944ca6a8..b3fbb746e7f0 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -239,18 +239,33 @@ ifdef PARSER_DEBUG
 endif
 
 # Try different combinations to accommodate systems that only have
-# python[2][-config] in weird combinations but always preferring
-# python2 and python2-config as per pep-0394. If python2 or python
-# aren't found, then python3 is used.
-PYTHON_AUTO := python
-PYTHON_AUTO := $(if $(call get-executable,python3),python3,$(PYTHON_AUTO))
-PYTHON_AUTO := $(if $(call get-executable,python),python,$(PYTHON_AUTO))
-PYTHON_AUTO := $(if $(call get-executable,python2),python2,$(PYTHON_AUTO))
-override PYTHON := $(call get-executable-or-default,PYTHON,$(PYTHON_AUTO))
-PYTHON_AUTO_CONFIG := \
-  $(if $(call get-executable,$(PYTHON)-config),$(PYTHON)-config,python-config)
-override PYTHON_CONFIG := \
-  $(call get-executable-or-default,PYTHON_CONFIG,$(PYTHON_AUTO_CONFIG))
+# python[2][3]-config in weird combinations in the following order of
+# priority from lowest to highest:
+#   * python3-config
+#   * python-config
+#   * python2-config as per pep-0394.
+#   * $(PYTHON)-config (If PYTHON is user supplied but PYTHON_CONFIG isn't)
+#
+PYTHON_AUTO := python-config
+PYTHON_AUTO := $(if $(call get-executable,python3-config),python3-config,$(PYTHON_AUTO))
+PYTHON_AUTO := $(if $(call get-executable,python-config),python-config,$(PYTHON_AUTO))
+PYTHON_AUTO := $(if $(call get-executable,python2-config),python2-config,$(PYTHON_AUTO))
+
+# If PYTHON is defined but PYTHON_CONFIG isn't, then take $(PYTHON)-config as if it was the user
+# supplied value for PYTHON_CONFIG. Because it's "user supplied", error out if it doesn't exist.
+ifdef PYTHON
+  ifndef PYTHON_CONFIG
+    PYTHON_CONFIG_AUTO := $(call get-executable,$(PYTHON)-config)
+    PYTHON_CONFIG := $(if $(PYTHON_CONFIG_AUTO),$(PYTHON_CONFIG_AUTO),\
+                          $(call $(error $(PYTHON)-config not found)))
+  endif
+endif
+
+# Select either auto detected python and python-config or use user supplied values if they are
+# defined. get-executable-or-default fails with an error if the first argument is supplied but
+# doesn't exist.
+override PYTHON_CONFIG := $(call get-executable-or-default,PYTHON_CONFIG,$(PYTHON_AUTO))
+override PYTHON := $(call get-executable-or-default,PYTHON,$(subst -config,,$(PYTHON_AUTO)))
 
 grep-libs  = $(filter -l%,$(1))
 strip-libs  = $(filter-out -l%,$(1))
-- 
2.28.0