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| author | Sam Ravnborg <sam@neptun.(none)> | 2007-10-14 22:21:35 +0200 |
|---|---|---|
| committer | Sam Ravnborg <sam@neptun.(none)> | 2007-10-14 22:21:35 +0200 |
| commit | a0f97e06a43cf524e616f09e6af3398e1e9c1c5b (patch) | |
| tree | 2503b24bdbc144aea9ea5bde6ead94b3406eaf98 /Documentation/kbuild/makefiles.txt | |
| parent | 9a39e273d4df0560c724c5fe71f6314a0583ca2b (diff) | |
kbuild: enable 'make CFLAGS=...' to add additional options to CC
The variable CFLAGS is a wellknown variable and the usage by
kbuild may result in unexpected behaviour.
On top of that several people over time has asked for a way to
pass in additional flags to gcc.
This patch replace use of CFLAGS with KBUILD_CFLAGS all over the
tree and enabling one to use:
make CFLAGS=...
to specify additional gcc commandline options.
One usecase is when trying to find gcc bugs but other
use cases has been requested too.
Patch was tested on following architectures:
alpha, arm, i386, x86_64, mips, sparc, sparc64, ia64, m68k
Test was simple to do a defconfig build, apply the patch and check
that nothing got rebuild.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Diffstat (limited to 'Documentation/kbuild/makefiles.txt')
| -rw-r--r-- | Documentation/kbuild/makefiles.txt | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 54bbfd37f15..1ca535bcc8c 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -294,7 +294,7 @@ more details, with real examples. This variable is necessary because the top Makefile owns the - variable $(CFLAGS) and uses it for compilation flags for the + variable $(KBUILD_CFLAGS) and uses it for compilation flags for the entire tree. $(EXTRA_AFLAGS) is a similar string for per-directory options @@ -437,6 +437,7 @@ more details, with real examples. -march=pentium-mmx if supported by $(CC), otherwise -march=i586. The second argument to cc-option is optional, and if omitted, cflags-y will be assigned no value if first option is not supported. + Note: cc-option uses KBUILD_CFLAGS for $(CC) options cc-option-yn cc-option-yn is used to check if gcc supports a given option @@ -452,6 +453,7 @@ more details, with real examples. option. When $(biarch) equals 'y', the expanded variables $(aflags-y) and $(cflags-y) will be assigned the values -a32 and -m32, respectively. + Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options cc-option-align gcc versions >= 3.0 changed the type of options used to specify @@ -463,10 +465,11 @@ more details, with real examples. cc-option-align = -falign Example: - CFLAGS += $(cc-option-align)-functions=4 + KBUILD_CFLAGS += $(cc-option-align)-functions=4 In the above example, the option -falign-functions=4 is used for gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used. + Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options cc-version cc-version returns a numerical version of the $(CC) compiler version. @@ -825,17 +828,17 @@ When kbuild executes, the following steps are followed (roughly): #arch/sparc64/Makefile AFLAGS += -m64 -mcpu=ultrasparc - CFLAGS $(CC) compiler flags + KBUILD_CFLAGS $(CC) compiler flags Default value - see top level Makefile Append or modify as required per architecture. - Often, the CFLAGS variable depends on the configuration. + Often, the KBUILD_CFLAGS variable depends on the configuration. Example: #arch/i386/Makefile cflags-$(CONFIG_M386) += -march=i386 - CFLAGS += $(cflags-y) + KBUILD_CFLAGS += $(cflags-y) Many arch Makefiles dynamically run the target C compiler to probe supported options: @@ -847,7 +850,7 @@ When kbuild executes, the following steps are followed (roughly): -march=pentium2,-march=i686) ... # Disable unit-at-a-time mode ... - CFLAGS += $(call cc-option,-fno-unit-at-a-time) + KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time) ... |