X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=Documentation%2Fkbuild%2Fmakefiles.txt;h=7a7753321a263f62c2a00c9d0e348716e701ac2c;hb=f3344c54cee4c446a39d046e47707ed9d259f72c;hp=4b3d6710c504c6257b7abd7d03129f9320e7c2c5;hpb=c4366889dda8110247be59ca41fddb82951a8c26;p=linux-2.6 diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 4b3d6710c5..7a7753321a 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -34,7 +34,7 @@ This document describes the Linux kernel Makefiles. --- 6.1 Set variables to tweak the build to the architecture --- 6.2 Add prerequisites to archprepare: --- 6.3 List directories to visit when descending - --- 6.4 Architecture specific boot images + --- 6.4 Architecture-specific boot images --- 6.5 Building non-kbuild targets --- 6.6 Commands useful for building a boot image --- 6.7 Custom kbuild commands @@ -124,7 +124,7 @@ more details, with real examples. Example: obj-y += foo.o - This tell kbuild that there is one object in that directory, named + This tells kbuild that there is one object in that directory, named foo.o. foo.o will be built from foo.c or foo.S. If foo.o shall be built as a module, the variable obj-m is used. @@ -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_$@ @@ -353,7 +351,7 @@ more details, with real examples. Special rules are used when the kbuild infrastructure does not provide the required support. A typical example is header files generated during the build process. - Another example are the architecture specific Makefiles which + Another example are the architecture-specific Makefiles which need special rules to prepare boot images etc. Special rules are written as normal Make rules. @@ -416,7 +414,7 @@ more details, with real examples. #arch/i386/kernel/Makefile vsyscall-flags += $(call ld-option, -Wl$(comma)--hash-style=sysv) - In the above example vsyscall-flags will be assigned the option + In the above example, vsyscall-flags will be assigned the option -Wl$(comma)--hash-style=sysv if it is supported by $(CC). The second argument is optional, and if supplied will be used if first argument is not supported. @@ -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 @@ -434,10 +433,11 @@ more details, with real examples. #arch/i386/Makefile cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) - In the above example cflags-y will be assigned the option + In the above example, cflags-y will be assigned the option -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. @@ -492,15 +494,51 @@ 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 The third parameter may be a text as in this example, but it may also be an expanded variable or a macro. + cc-fullversion + cc-fullversion is useful when the exact version of gcc is needed. + One typical use-case is when a specific GCC version is broken. + cc-fullversion points out a more specific version than cc-version does. + + Example: + #arch/powerpc/Makefile + $(Q)if test "$(call cc-fullversion)" = "040200" ; then \ + echo -n '*** GCC-4.2.0 cannot compile the 64-bit powerpc ' ; \ + false ; \ + fi + + 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 := $(call cc-cross-prefix, m68k-linux-gnu-) + endif + endif === 4 Host Program support @@ -750,10 +788,10 @@ When kbuild executes, the following steps are followed (roughly): located at the root of the obj tree. The very first objects linked are listed in head-y, assigned by arch/$(ARCH)/Makefile. -7) Finally, the architecture specific part does any required post processing +7) Finally, the architecture-specific part does any required post processing and builds the final bootimage. - This includes building boot records - - Preparing initrd images and thelike + - Preparing initrd images and the like --- 6.1 Set variables to tweak the build to the architecture @@ -766,8 +804,8 @@ 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 @@ -803,26 +841,26 @@ 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: @@ -834,7 +872,7 @@ 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) ... @@ -880,7 +918,7 @@ When kbuild executes, the following steps are followed (roughly): $(head-y) lists objects to be linked first in vmlinux. $(libs-y) lists directories where a lib.a archive can be located. - The rest lists directories where a built-in.o object file can be + The rest list directories where a built-in.o object file can be located. $(init-y) objects will be located after $(head-y). @@ -888,7 +926,7 @@ When kbuild executes, the following steps are followed (roughly): $(core-y), $(libs-y), $(drivers-y) and $(net-y). The top level Makefile defines values for all generic directories, - and arch/$(ARCH)/Makefile only adds architecture specific directories. + and arch/$(ARCH)/Makefile only adds architecture-specific directories. Example: #arch/sparc64/Makefile @@ -897,7 +935,7 @@ When kbuild executes, the following steps are followed (roughly): drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ ---- 6.4 Architecture specific boot images +--- 6.4 Architecture-specific boot images An arch Makefile specifies goals that take the vmlinux file, compress it, wrap it in bootstrapping code, and copy the resulting files @@ -924,7 +962,7 @@ When kbuild executes, the following steps are followed (roughly): "$(Q)$(MAKE) $(build)=