Commit 8417da6f authored by Michal Marek's avatar Michal Marek
Browse files

kbuild: Fix passing -Wno-* options to gcc 4.4+ 

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: default avatarStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: default avatarMichal Marek <mmarek@suse.cz>
parent bffd2020

Documentation/kbuild/makefiles.txt

+12 −0
Original line number Diff line number Diff line
@@ -501,6 +501,18 @@ 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

Makefile

+2 −2
Original line number Diff line number Diff line
@@ -569,7 +569,7 @@ endif 


# This warning generated too much noise in a regular build.

# Use make W=1 to enable this warning (see scripts/Makefile.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
@@ -616,7 +616,7 @@ 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)

scripts/Kbuild.include

+5 −0
Original line number Diff line number Diff line
@@ -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))

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