From 824b5a40dd3de0bd58fa306f4be8d6e13e1c327d Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@suse.com>
Date: Wed, 23 Aug 2023 09:25:52 +0200
Subject: [PATCH] build: make cc-option properly deal with unrecognized
 sub-options

In options like -march=, it may be only the sub-option which is
unrecognized by the compiler. In such an event the error message often
splits option and argument, typically saying something like "bad value
'<argument>' for '<option>'. Instead of extend the grep invocation, stop
parsing compiler output altogether. Instead substitute -Wno-* options by
their -W* counterparts for probing (obviously assuming that such a
counterpart always exists).

Suggested-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
---
 Config.mk | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/Config.mk b/Config.mk
index dc3afaa47e..29c29f8d7f 100644
--- a/Config.mk
+++ b/Config.mk
@@ -85,17 +85,17 @@ PYTHON_PREFIX_ARG ?= --prefix="$(prefix)"
 
 # cc-option: Check if compiler supports first option, else fall back to second.
 #
-# This is complicated by the fact that unrecognised -Wno-* options:
+# This is complicated by the fact that with most gcc versions unrecognised
+# -Wno-* options:
 #   (a) are ignored unless the compilation emits a warning; and
 #   (b) even then produce a warning rather than an error
-# To handle this we do a test compile, passing the option-under-test, on a code
-# fragment that will always produce a warning (integer assigned to pointer).
-# We then grep for the option-under-test in the compiler's output, the presence
-# of which would indicate an "unrecognized command-line option" warning/error.
+# Further Clang also only warns for unrecognised -W* options.  To handle this
+# we do a test compile, substituting -Wno-* by -W* and adding -Werror.  This
+# way all unrecognised options are diagnosed uniformly, allowing us to merely
+# check exit status.
 #
 # Usage: cflags-y += $(call cc-option,$(CC),-march=winchip-c6,-march=i586)
-cc-option = $(shell if test -z "`echo 'void*p=1;' | \
-              $(1) $(2) -c -o /dev/null -x c - 2>&1 | grep -- $(2:-Wa$(comma)%=%) -`"; \
+cc-option = $(shell if $(1) $(2:-Wno-%=-W%) -Werror -c -o /dev/null -x c /dev/null >/dev/null 2>&1; \
               then echo "$(2)"; else echo "$(3)"; fi ;)
 
 # cc-option-add: Add an option to compilation flags, but only if supported.