X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=Documentation%2Fkbuild%2Fmakefiles.txt;h=7a7753321a263f62c2a00c9d0e348716e701ac2c;hb=46015977e70f672ae6b20a1b5fb1e361208365ba;hp=1ca535bcc8c7d3adeae372d74bdea0fc801a9198;hpb=a0f97e06a43cf524e616f09e6af3398e1e9c1c5b;p=linux-2.6 diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 1ca535bcc8..7a7753321a 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -276,40 +276,39 @@ more details, with real examples. --- 3.7 Compilation flags - EXTRA_CFLAGS, EXTRA_AFLAGS, EXTRA_LDFLAGS + 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 $(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) is a string for per-directory options to $(LD). + ldflags-y is a string for per-directory options to $(LD). Example: #arch/m68k/fpsp040/Makefile - EXTRA_LDFLAGS := -x + ldflags-y := -x CFLAGS_$@, AFLAGS_$@ @@ -424,6 +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 @@ -494,9 +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 @@ -518,6 +518,28 @@ more details, with real examples. In this example for a specific GCC version the build will error out explaining to the user why it stops. + cc-cross-prefix + cc-cross-prefix is used to check if there exists a $(CC) in path with + one of the listed prefixes. The first prefix where there exist a + prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found + then nothing is returned. + Additional prefixes are separated by a single space in the + call of cc-cross-prefix. + This functionality is useful for architecture Makefiles that try + to set CROSS_COMPILE to well-known values but may have several + values to select between. + It is recommended only to try to set CROSS_COMPILE if it is a cross + build (host arch is different from target arch). And if CROSS_COMPILE + is already set then leave it with the old value. + + Example: + #arch/m68k/Makefile + ifneq ($(SUBARCH),$(ARCH)) + ifeq ($(CROSS_COMPILE),) + CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-) + endif + endif + === 4 Host Program support Kbuild supports building executables on the host for use during the @@ -782,7 +804,7 @@ When kbuild executes, the following steps are followed (roughly): Example: #arch/s390/Makefile LDFLAGS := -m elf_s390 - Note: EXTRA_LDFLAGS can be used to further customise + Note: ldflags-y can be used to further customise the flags used. See chapter 3.7. LDFLAGS_MODULE Options for $(LD) when linking modules @@ -819,14 +841,14 @@ 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 KBUILD_CFLAGS $(CC) compiler flags @@ -1098,8 +1120,8 @@ When kbuild executes, the following steps are followed (roughly): specified options when building the target vmlinux.lds. When building the *.lds target, kbuild uses the variables: - CPPFLAGS : Set in top-level Makefile - EXTRA_CPPFLAGS : May be set in the kbuild makefile + KBUILD_CPPFLAGS : Set in top-level Makefile + cppflags-y : May be set in the kbuild makefile CPPFLAGS_$(@F) : Target specific flags. Note that the full filename is used in this assignment.