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kbuild: enable 'make CFLAGS=...' to add additional options to CC

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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 <[email protected]>
This commit is contained in:
Sam Ravnborg 2007-10-14 22:21:35 +02:00
commit a0f97e06a4
46 changed files with 137 additions and 136 deletions
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15
Documentation/kbuild/makefiles.txt
View file

@ -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)
...