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Diffstat (limited to 'Documentation/kbuild/makefiles.txt')
| -rw-r--r-- | Documentation/kbuild/makefiles.txt | 192 |
1 files changed, 150 insertions, 42 deletions
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 0ef00bd6e54..c600e2f44a6 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -33,18 +33,21 @@ This document describes the Linux kernel Makefiles. === 6 Architecture 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 - --- 6.5 Building non-kbuild targets - --- 6.6 Commands useful for building a boot image - --- 6.7 Custom kbuild commands - --- 6.8 Preprocessing linker scripts + --- 6.2 Add prerequisites to archheaders: + --- 6.3 Add prerequisites to archprepare: + --- 6.4 List directories to visit when descending + --- 6.5 Architecture-specific boot images + --- 6.6 Building non-kbuild targets + --- 6.7 Commands useful for building a boot image + --- 6.8 Custom kbuild commands + --- 6.9 Preprocessing linker scripts + --- 6.10 Generic header files === 7 Kbuild syntax for exported headers --- 7.1 header-y - --- 7.2 objhdr-y + --- 7.2 genhdr-y --- 7.3 destination-y + --- 7.4 generic-y === 8 Kbuild Variables === 9 Makefile language @@ -250,7 +253,7 @@ more details, with real examples. This will create a library lib.a based on delay.o. For kbuild to actually recognize that there is a lib.a being built, the directory shall be listed in libs-y. - See also "6.3 List directories to visit when descending". + See also "6.4 List directories to visit when descending". Use of lib-y is normally restricted to lib/ and arch/*/lib. @@ -439,7 +442,7 @@ more details, with real examples. specified if first option are not supported. Example: - #arch/i386/kernel/Makefile + #arch/x86/kernel/Makefile vsyscall-flags += $(call cc-ldoption, -Wl$(comma)--hash-style=sysv) In the above example, vsyscall-flags will be assigned the option @@ -458,7 +461,7 @@ more details, with real examples. supported to use an optional second option. Example: - #arch/i386/Makefile + #arch/x86/Makefile cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) In the above example, cflags-y will be assigned the option @@ -499,6 +502,18 @@ more details, with real examples. gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used. Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options + cc-disable-warning + cc-disable-warning checks if gcc supports a given warning and returns + the commandline switch to disable it. This special function is needed, + because gcc 4.4 and later accept any unknown -Wno-* option and only + warn about it if there is another warning in the source file. + + Example: + KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) + + In the above example, -Wno-unused-but-set-variable will be added to + KBUILD_CFLAGS only if gcc really accepts it. + cc-version cc-version returns a numerical version of the $(CC) compiler version. The format is <major><minor> where both are two digits. So for example @@ -508,7 +523,7 @@ more details, with real examples. even though the option was accepted by gcc. Example: - #arch/i386/Makefile + #arch/x86/Makefile cflags-y += $(shell \ if [ $(call cc-version) -ge 0300 ] ; then \ echo "-mregparm=3"; fi ;) @@ -578,7 +593,7 @@ more details, with real examples. Example: #Makefile - LDFLAGS_vmlinux += $(call really-ld-option, -X) + LDFLAGS_vmlinux += $(call ld-option, -X) === 4 Host Program support @@ -788,7 +803,7 @@ but in the architecture makefiles where the kbuild infrastructure is not sufficient this sometimes needs to be explicit. Example: - #arch/i386/boot/Makefile + #arch/x86/boot/Makefile subdir- := compressed/ The above assignment instructs kbuild to descend down in the @@ -798,12 +813,12 @@ To support the clean infrastructure in the Makefiles that builds the final bootimage there is an optional target named archclean: Example: - #arch/i386/Makefile + #arch/x86/Makefile archclean: - $(Q)$(MAKE) $(clean)=arch/i386/boot + $(Q)$(MAKE) $(clean)=arch/x86/boot -When "make clean" is executed, make will descend down in arch/i386/boot, -and clean as usual. The Makefile located in arch/i386/boot/ may use +When "make clean" is executed, make will descend down in arch/x86/boot, +and clean as usual. The Makefile located in arch/x86/boot/ may use the subdir- trick to descend further down. Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is @@ -868,7 +883,7 @@ When kbuild executes, the following steps are followed (roughly): LDFLAGS_vmlinux uses the LDFLAGS_$@ support. Example: - #arch/i386/Makefile + #arch/x86/Makefile LDFLAGS_vmlinux := -e stext OBJCOPYFLAGS objcopy flags @@ -906,14 +921,15 @@ When kbuild executes, the following steps are followed (roughly): Often, the KBUILD_CFLAGS variable depends on the configuration. Example: - #arch/i386/Makefile - cflags-$(CONFIG_M386) += -march=i386 + #arch/x86/boot/compressed/Makefile + cflags-$(CONFIG_X86_32) := -march=i386 + cflags-$(CONFIG_X86_64) := -mcmodel=small KBUILD_CFLAGS += $(cflags-y) Many arch Makefiles dynamically run the target C compiler to probe supported options: - #arch/i386/Makefile + #arch/x86/Makefile ... cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ @@ -955,7 +971,25 @@ When kbuild executes, the following steps are followed (roughly): used when linking modules. This is often a linker script. From commandline LDFLAGS_MODULE shall be used (see kbuild.txt). ---- 6.2 Add prerequisites to archprepare: + KBUILD_ARFLAGS Options for $(AR) when creating archives + + $(KBUILD_ARFLAGS) set by the top level Makefile to "D" (deterministic + mode) if this option is supported by $(AR). + +--- 6.2 Add prerequisites to archheaders: + + The archheaders: rule is used to generate header files that + may be installed into user space by "make header_install" or + "make headers_install_all". In order to support + "make headers_install_all", this target has to be able to run + on an unconfigured tree, or a tree configured for another + architecture. + + It is run before "make archprepare" when run on the + architecture itself. + + +--- 6.3 Add prerequisites to archprepare: The archprepare: rule is used to list prerequisites that need to be built before starting to descend down in the subdirectories. @@ -971,7 +1005,7 @@ When kbuild executes, the following steps are followed (roughly): generating offset header files. ---- 6.3 List directories to visit when descending +--- 6.4 List directories to visit when descending An arch Makefile cooperates with the top Makefile to define variables which specify how to build the vmlinux file. Note that there is no @@ -1000,7 +1034,7 @@ When kbuild executes, the following steps are followed (roughly): drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ ---- 6.4 Architecture-specific boot images +--- 6.5 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 @@ -1019,8 +1053,8 @@ When kbuild executes, the following steps are followed (roughly): into the arch/$(ARCH)/boot/Makefile. Example: - #arch/i386/Makefile - boot := arch/i386/boot + #arch/x86/Makefile + boot := arch/x86/boot bzImage: vmlinux $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ @@ -1032,7 +1066,7 @@ When kbuild executes, the following steps are followed (roughly): To support this, $(archhelp) must be defined. Example: - #arch/i386/Makefile + #arch/x86/Makefile define archhelp echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' endif @@ -1046,12 +1080,12 @@ When kbuild executes, the following steps are followed (roughly): from vmlinux. Example: - #arch/i386/Makefile + #arch/x86/Makefile all: bzImage When "make" is executed without arguments, bzImage will be built. ---- 6.5 Building non-kbuild targets +--- 6.6 Building non-kbuild targets extra-y @@ -1064,14 +1098,14 @@ When kbuild executes, the following steps are followed (roughly): 2) kbuild knows what files to delete during "make clean" Example: - #arch/i386/kernel/Makefile + #arch/x86/kernel/Makefile extra-y := head.o init_task.o In this example, extra-y is used to list object files that shall be built, but shall not be linked as part of built-in.o. ---- 6.6 Commands useful for building a boot image +--- 6.7 Commands useful for building a boot image Kbuild provides a few macros that are useful when building a boot image. @@ -1093,7 +1127,7 @@ When kbuild executes, the following steps are followed (roughly): always be built. Assignments to $(targets) are without $(obj)/ prefix. if_changed may be used in conjunction with custom commands as - defined in 6.7 "Custom kbuild commands". + defined in 6.8 "Custom kbuild commands". Note: It is a typical mistake to forget the FORCE prerequisite. Another common pitfall is that whitespace is sometimes @@ -1114,7 +1148,7 @@ When kbuild executes, the following steps are followed (roughly): Compress target. Use maximum compression to compress target. Example: - #arch/i386/boot/Makefile + #arch/x86/boot/Makefile LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext @@ -1136,8 +1170,47 @@ When kbuild executes, the following steps are followed (roughly): resulting in the target file being recompiled for no obvious reason. + dtc + Create flattened device tree blob object suitable for linking + into vmlinux. Device tree blobs linked into vmlinux are placed + in an init section in the image. Platform code *must* copy the + blob to non-init memory prior to calling unflatten_device_tree(). + + To use this command, simply add *.dtb into obj-y or targets, or make + some other target depend on %.dtb + + A central rule exists to create $(obj)/%.dtb from $(src)/%.dts; + architecture Makefiles do no need to explicitly write out that rule. ---- 6.7 Custom kbuild commands + Example: + targets += $(dtb-y) + clean-files += *.dtb + DTC_FLAGS ?= -p 1024 + + dtc_cpp + This is just like dtc as describe above, except that the C pre- + processor is invoked upon the .dtsp file before compiling the result + with dtc. + + In order for build dependencies to work, all files compiled using + dtc_cpp must use the C pre-processor's #include functionality and not + dtc's /include/ functionality. + + Using the C pre-processor allows use of #define to create named + constants. In turn, the #defines will typically appear in a header + file, which may be shared with regular C code. Since the dtc language + represents a data structure rather than code in C syntax, similar + restrictions are placed on a header file included by a device tree + file as for a header file included by an assembly language file. + In particular, the C pre-processor is passed -x assembler-with-cpp, + which sets macro __ASSEMBLY__. __DTS__ is also set. These allow header + files to restrict their content to that compatible with device tree + source. + + A central rule exists to create $(obj)/%.dtb from $(src)/%.dtsp; + architecture Makefiles do no need to explicitly write out that rule. + +--- 6.8 Custom kbuild commands When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand of a command is normally displayed. @@ -1159,12 +1232,12 @@ When kbuild executes, the following steps are followed (roughly): When updating the $(obj)/bzImage target, the line - BUILD arch/i386/boot/bzImage + BUILD arch/x86/boot/bzImage will be displayed with "make KBUILD_VERBOSE=0". ---- 6.8 Preprocessing linker scripts +--- 6.9 Preprocessing linker scripts When the vmlinux image is built, the linker script arch/$(ARCH)/kernel/vmlinux.lds is used. @@ -1173,7 +1246,7 @@ When kbuild executes, the following steps are followed (roughly): kbuild knows .lds files and includes a rule *lds.S -> *lds. Example: - #arch/i386/kernel/Makefile + #arch/x86/kernel/Makefile always := vmlinux.lds #Makefile @@ -1194,6 +1267,14 @@ When kbuild executes, the following steps are followed (roughly): The kbuild infrastructure for *lds file are used in several architecture-specific files. +--- 6.10 Generic header files + + The directory include/asm-generic contains the header files + that may be shared between individual architectures. + The recommended approach how to use a generic header file is + to list the file in the Kbuild file. + See "7.4 generic-y" for further info on syntax etc. + === 7 Kbuild syntax for exported headers The kernel include a set of headers that is exported to userspace. @@ -1226,15 +1307,15 @@ See subsequent chapter for the syntax of the Kbuild file. Subdirectories are visited before their parent directories. - --- 7.2 objhdr-y + --- 7.2 genhdr-y - objhdr-y specifies generated files to be exported. + genhdr-y specifies generated files to be exported. Generated files are special as they need to be looked up in another directory when doing 'make O=...' builds. Example: #include/linux/Kbuild - objhdr-y += version.h + genhdr-y += version.h --- 7.3 destination-y @@ -1250,6 +1331,32 @@ See subsequent chapter for the syntax of the Kbuild file. In the example above all exported headers in the Kbuild file will be located in the directory "include/linux" when exported. + --- 7.4 generic-y + + If an architecture uses a verbatim copy of a header from + include/asm-generic then this is listed in the file + arch/$(ARCH)/include/asm/Kbuild like this: + + Example: + #arch/x86/include/asm/Kbuild + generic-y += termios.h + generic-y += rtc.h + + During the prepare phase of the build a wrapper include + file is generated in the directory: + + arch/$(ARCH)/include/generated/asm + + When a header is exported where the architecture uses + the generic header a similar wrapper is generated as part + of the set of exported headers in the directory: + + usr/include/asm + + The generated wrapper will in both cases look like the following: + + Example: termios.h + #include <asm-generic/termios.h> === 8 Kbuild Variables @@ -1310,7 +1417,8 @@ The top Makefile exports the following variables: If this variable is specified, will cause modules to be stripped after they are installed. If INSTALL_MOD_STRIP is '1', then the default option --strip-debug will be used. Otherwise, - INSTALL_MOD_STRIP will used as the option(s) to the strip command. + INSTALL_MOD_STRIP value will be used as the option(s) to the strip + command. === 9 Makefile language |