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Subject[PATCH 88/91] kbuild: Fix passing -Wno-* options to gcc 4.4+
2.6.27-longterm review patch.  If anyone has any objections, please let us know.

------------------

commit 8417da6f2128008c431c7d130af6cd3d9079922e upstream.

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: Greg Kroah-Hartman <gregkh@suse.de>
---
Documentation/kbuild/makefiles.txt | 12 ++++++++++++
Makefile | 4 ++--
scripts/Kbuild.include | 5 +++++
3 files changed, 19 insertions(+), 2 deletions(-)

Index: longterm-2.6.27/Documentation/kbuild/makefiles.txt
===================================================================
--- longterm-2.6.27.orig/Documentation/kbuild/makefiles.txt 2012-02-05 22:34:32.253915069 +0100
+++ longterm-2.6.27/Documentation/kbuild/makefiles.txt 2012-02-05 22:34:47.409917106 +0100
@@ -471,6 +471,18 @@
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: longterm-2.6.27/Makefile
===================================================================
--- longterm-2.6.27.orig/Makefile 2012-02-05 22:34:47.271916824 +0100
+++ longterm-2.6.27/Makefile 2012-02-05 22:34:47.412915249 +0100
@@ -531,7 +531,7 @@
KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)

# 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
@@ -561,7 +561,7 @@
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" optimzations for signed / pointers
KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow)
Index: longterm-2.6.27/scripts/Kbuild.include
===================================================================
--- longterm-2.6.27.orig/scripts/Kbuild.include 2012-02-05 22:34:32.256915061 +0100
+++ longterm-2.6.27/scripts/Kbuild.include 2012-02-05 22:34:47.418914568 +0100
@@ -117,6 +117,11 @@
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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