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

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, 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 <>
Signed-off-by: default avatarMichal Marek <>
parent bffd2020
......@@ -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 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.
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 returns a numerical version of the $(CC) compiler version.
The format is <major><minor> where both are two digits. So for example
......@@ -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/
KBUILD_CFLAGS += $(call cc-option, -Wno-unused-but-set-variable)
KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
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)
......@@ -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/ $(CC))
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