diff options
Diffstat (limited to 'Documentation/kbuild/makefiles.txt')
| -rw-r--r-- | Documentation/kbuild/makefiles.txt | 62 |
1 files changed, 32 insertions, 30 deletions
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index e08ef8759a0..f099b814d38 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -276,41 +276,39 @@ more details, with real examples. --- 3.7 Compilation flags - EXTRA_CFLAGS, EXTRA_AFLAGS, EXTRA_LDFLAGS, EXTRA_ARFLAGS + ccflags-y, asflags-y and ldflags-y + The three flags listed above applies only to the kbuild makefile + where they are assigned. They are used for all the normal + cc, as and ld invocation happenign during a recursive build. + Note: Flags with the same behaviour were previously named: + EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. + They are yet supported but their use are deprecated. - All the EXTRA_ variables apply only to the kbuild makefile - where they are assigned. The EXTRA_ variables apply to all - commands executed in the kbuild makefile. - - $(EXTRA_CFLAGS) specifies options for compiling C files with - $(CC). + ccflags-y specifies options for compiling C files with $(CC). Example: # drivers/sound/emu10k1/Makefile - EXTRA_CFLAGS += -I$(obj) - ifdef DEBUG - EXTRA_CFLAGS += -DEMU10K1_DEBUG - endif + ccflags-y += -I$(obj) + ccflags-$(DEBUG) += -DEMU10K1_DEBUG 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 + asflags-y is a similar string for per-directory options when compiling assembly language source. Example: #arch/x86_64/kernel/Makefile - EXTRA_AFLAGS := -traditional + asflags-y := -traditional - $(EXTRA_LDFLAGS) and $(EXTRA_ARFLAGS) are similar strings for - per-directory options to $(LD) and $(AR). + ldflags-y is a string for per-directory options to $(LD). Example: #arch/m68k/fpsp040/Makefile - EXTRA_LDFLAGS := -x + ldflags-y := -x CFLAGS_$@, AFLAGS_$@ @@ -425,6 +423,7 @@ more details, with real examples. as-instr checks if the assembler reports a specific instruction and then outputs either option1 or option2 C escapes are supported in the test instruction + Note: as-instr-option uses KBUILD_AFLAGS for $(AS) options cc-option cc-option is used to check if $(CC) supports a given option, and not @@ -438,6 +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 @@ -453,6 +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 @@ -464,10 +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. @@ -492,9 +494,9 @@ more details, with real examples. Example: #fs/reiserfs/Makefile - EXTRA_CFLAGS := $(call cc-ifversion, -lt, 0402, -O1) + ccflags-y := $(call cc-ifversion, -lt, 0402, -O1) - In this example, EXTRA_CFLAGS will be assigned the value -O1 if the + In this example, ccflags-y will be assigned the value -O1 if the $(CC) version is less than 4.2. cc-ifversion takes all the shell operators: -eq, -ne, -lt, -le, -gt, and -ge @@ -780,8 +782,8 @@ When kbuild executes, the following steps are followed (roughly): Example: #arch/s390/Makefile LDFLAGS := -m elf_s390 - Note: EXTRA_LDFLAGS and LDFLAGS_$@ can be used to further customise - the flags used. See chapter 7. + Note: ldflags-y can be used to further customise + the flags used. See chapter 3.7. LDFLAGS_MODULE Options for $(LD) when linking modules @@ -817,26 +819,26 @@ When kbuild executes, the following steps are followed (roughly): In this example, the binary $(obj)/image is a binary version of vmlinux. The usage of $(call if_changed,xxx) will be described later. - AFLAGS $(AS) assembler flags + KBUILD_AFLAGS $(AS) assembler flags Default value - see top level Makefile Append or modify as required per architecture. Example: #arch/sparc64/Makefile - AFLAGS += -m64 -mcpu=ultrasparc + KBUILD_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: @@ -848,7 +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 += $(call cc-option,-fno-unit-at-a-time) ... @@ -1096,8 +1098,8 @@ When kbuild executes, the following steps are followed (roughly): specified options when building the target vmlinux.lds. When building the *.lds target, kbuild uses the variables: - CPPFLAGS : Set in top-level Makefile - EXTRA_CPPFLAGS : May be set in the kbuild makefile + KBUILD_CPPFLAGS : Set in top-level Makefile + cppflags-y : May be set in the kbuild makefile CPPFLAGS_$(@F) : Target specific flags. Note that the full filename is used in this assignment. |