[PATCH v4] kconfig: check for pkg-config on make {menu,n,g,x}config

[Randy Dunlap]

From: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>

Each of 'make {menu,n,g,x}config' uses (needs) pkg-config to make sure
that other required files are present and to determine build flags
settings, but none of these check that pkg-config itself is present.
Add a check for all 4 of these targets and update
Documentation/process/changes.rst to mention 'pkg-config'.

Fixes kernel bugzilla #77511:
https://bugzilla.kernel.org/show_bug.cgi?id=77511

Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: BjÃrn Forsman <bjorn.forsman@xxxxxxxxx>
---
v4: apply Masahiro's suggestions

Strictly speaking, pkg-config is not required if someone is only
using 'make {menu,n}config' since there are fallbacks for those
two targets.

 Documentation/process/changes.rst  |    8 ++++++++
 scripts/kconfig/Makefile           |    1 +
 scripts/kconfig/check-pkgconfig.sh |    8 ++++++++
 3 files changed, 17 insertions(+)

--- linux-next-20180628.orig/scripts/kconfig/Makefile
+++ linux-next-20180628/scripts/kconfig/Makefile
@@ -215,6 +215,7 @@ $(obj)/zconf.tab.o: $(obj)/zconf.lex.c
 
 # check if necessary packages are available, and configure build flags
 define filechk_conf_cfg
+	$(CONFIG_SHELL) $(srctree)/scripts/kconfig/check-pkgconfig.sh; \
 	$(CONFIG_SHELL) $<
 endef
 
--- /dev/null
+++ linux-next-20180628/scripts/kconfig/check-pkgconfig.sh
@@ -0,0 +1,8 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# Check for pkg-config presence
+
+if [ -z $(command -v pkg-config) ]; then
+	echo "'make *config' requires 'pkg-config'. Please install it." 1>&2
+	exit 1
+fi
--- linux-next-20180628.orig/Documentation/process/changes.rst
+++ linux-next-20180628/Documentation/process/changes.rst
@@ -81,6 +81,14 @@ The build system has, as of 4.13, switch
 rather than incremental linking (`ld -r`) for built-in.a intermediate steps.
 This requires binutils 2.20 or newer.
 
+pkg-config
+----------
+
+The build system, as of 4.18, requires pkg-config to check for installed
+kconfig tools and to determine flags settings for use in
+'make {menu,n,g,x}config'.  Previously pkg-config was being used but not
+verified or documented.
+
 Flex
 ----