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: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Michal Marek <mmarek@suse.cz>
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3 changed files with 19 additions and 2 deletions
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@ -501,6 +501,18 @@ more details, with real examples.
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gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used.
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Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options
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cc-disable-warning
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cc-disable-warning checks if gcc supports a given warning and returns
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the commandline switch to disable it. This special function is needed,
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because gcc 4.4 and later accept any unknown -Wno-* option and only
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warn about it if there is another warning in the source file.
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Example:
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KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
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In the above example, -Wno-unused-but-set-variable will be added to
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KBUILD_CFLAGS only if gcc really accepts it.
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cc-version
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cc-version returns a numerical version of the $(CC) compiler version.
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The format is <major><minor> where both are two digits. So for example
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4
Makefile
4
Makefile
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@ -569,7 +569,7 @@ endif
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# This warning generated too much noise in a regular build.
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# Use make W=1 to enable this warning (see scripts/Makefile.build)
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KBUILD_CFLAGS += $(call cc-option, -Wno-unused-but-set-variable)
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KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
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ifdef CONFIG_FRAME_POINTER
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KBUILD_CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
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@ -616,7 +616,7 @@ CHECKFLAGS += $(NOSTDINC_FLAGS)
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KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
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# disable pointer signed / unsigned warnings in gcc 4.0
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KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)
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KBUILD_CFLAGS += $(call cc-disable-warning, pointer-sign)
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# disable invalid "can't wrap" optimizations for signed / pointers
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KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow)
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@ -118,6 +118,11 @@ cc-option-yn = $(call try-run,\
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cc-option-align = $(subst -functions=0,,\
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$(call cc-option,-falign-functions=0,-malign-functions=0))
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# cc-disable-warning
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# Usage: cflags-y += $(call cc-disable-warning,unused-but-set-variable)
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cc-disable-warning = $(call try-run,\
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$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -xc /dev/null -o "$$TMP",-Wno-$(strip $(1)))
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# cc-version
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# Usage gcc-ver := $(call cc-version)
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cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
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