[PATCH] [2/98] kbuild: Fix passing -Wno-* options to gcc 4.4+

Andi Kleen
2011-07-27T00:42:45Z

From: Michal Marek <mmarek@suse.cz>

[ upstream commit 8417da6f2128008c431c7d130af6cd3d9079922e ]

Starting with 4.4, gcc will happily accept -Wno-<anything> in the
cc-option test and complain later when compiling a file that has some
other warning. This rather unexpected behavior is intentional as per
http://gcc.gnu.org/PR28322, so work around it by testing for support of
the opposite option (without the no-). Introduce a new Makefile function
cc-disable-warning that does this and update two uses of cc-option in
the toplevel Makefile.

Reported-and-tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/Documentation/kbuild/makefiles.txt
===================================================================
--- linux-2.6.35.y.orig/Documentation/kbuild/makefiles.txt
+++ linux-2.6.35.y/Documentation/kbuild/makefiles.txt
@@ -502,6 +502,18 @@ more details, with real examples.
gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used.
Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options

+ cc-disable-warning
+ cc-disable-warning checks if gcc supports a given warning and returns
+ the commandline switch to disable it. This special function is needed,
+ because gcc 4.4 and later accept any unknown -Wno-* option and only
+ warn about it if there is another warning in the source file.
+
+ Example:
+ KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
+
+ In the above example, -Wno-unused-but-set-variable will be added to
+ KBUILD_CFLAGS only if gcc really accepts it.
+
cc-version
cc-version returns a numerical version of the $(CC) compiler version.
The format is <major><minor> where both are two digits. So for example
Index: linux-2.6.35.y/Makefile
===================================================================
--- linux-2.6.35.y.orig/Makefile
+++ linux-2.6.35.y/Makefile
@@ -547,7 +547,7 @@ KBUILD_CFLAGS += $(call cc-option, -fno-
endif

# This warning generated too much noise in a regular build.
-KBUILD_CFLAGS += $(call cc-option, -Wno-unused-but-set-variable)
+KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)

ifdef CONFIG_FRAME_POINTER
KBUILD_CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
@@ -577,7 +577,7 @@ CHECKFLAGS += $(NOSTDINC_FLAGS)
KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)

# disable pointer signed / unsigned warnings in gcc 4.0
-KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)
+KBUILD_CFLAGS += $(call cc-disable-warning, pointer-sign)

# disable invalid "can't wrap" optimizations for signed / pointers
KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow)
Index: linux-2.6.35.y/scripts/Kbuild.include
===================================================================
--- linux-2.6.35.y.orig/scripts/Kbuild.include
+++ linux-2.6.35.y/scripts/Kbuild.include
@@ -118,6 +118,11 @@ cc-option-yn = $(call try-run,\
cc-option-align = $(subst -functions=0,,\
$(call cc-option,-falign-functions=0,-malign-functions=0))

+# cc-disable-warning
+# Usage: cflags-y += $(call cc-disable-warning,unused-but-set-variable)
+cc-disable-warning = $(call try-run,\
+ $(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -xc /dev/null -o "$$TMP",-Wno-$(strip $(1)))
+
# cc-version
# Usage gcc-ver := $(call cc-version)
cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))