diff options
| -rw-r--r-- | Documentation/kbuild/makefiles.txt | 83 |
1 files changed, 43 insertions, 40 deletions
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 3d2f88ea14a5..b7d6abb501a6 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -22,7 +22,7 @@ This document describes the Linux kernel Makefiles. === 4 Host Program support --- 4.1 Simple Host Program --- 4.2 Composite Host Programs - --- 4.3 Defining shared libraries + --- 4.3 Defining shared libraries --- 4.4 Using C++ for host programs --- 4.5 Controlling compiler options for host programs --- 4.6 When host programs are actually built @@ -69,7 +69,7 @@ architecture-specific information to the top Makefile. Each subdirectory has a kbuild Makefile which carries out the commands passed down from above. The kbuild Makefile uses information from the -.config file to construct various file lists used by kbuild to build +.config file to construct various file lists used by kbuild to build any built-in or modular targets. scripts/Makefile.* contains all the definitions/rules etc. that @@ -203,9 +203,9 @@ more details, with real examples. Example: #fs/ext2/Makefile obj-$(CONFIG_EXT2_FS) += ext2.o - ext2-y := balloc.o bitmap.o + ext2-y := balloc.o bitmap.o ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o - + In this example, xattr.o is only part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) evaluates to 'y'. @@ -244,7 +244,7 @@ more details, with real examples. 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". - + Use of lib-y is normally restricted to lib/ and arch/*/lib. --- 3.6 Descending down in directories @@ -408,7 +408,7 @@ more details, with real examples. if first argument is not supported. ld-option - ld-option is used to check if $(CC) when used to link object files + ld-option is used to check if $(CC) when used to link object files supports the given option. An optional second option may be specified if first option are not supported. @@ -435,7 +435,7 @@ more details, with real examples. cflags-y will be assigned no value if first option is not supported. cc-option-yn - cc-option-yn is used to check if gcc supports a given option + cc-option-yn is used to check if gcc supports a given option and return 'y' if supported, otherwise 'n'. Example: @@ -443,7 +443,7 @@ more details, with real examples. biarch := $(call cc-option-yn, -m32) aflags-$(biarch) += -a32 cflags-$(biarch) += -m32 - + In the above example, $(biarch) is set to y if $(CC) supports the -m32 option. When $(biarch) equals 'y', the expanded variables $(aflags-y) and $(cflags-y) will be assigned the values -a32 and -m32, @@ -457,13 +457,13 @@ more details, with real examples. cc-option-align = -malign gcc >= 3.00 cc-option-align = -falign - + Example: 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. - + 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 @@ -491,7 +491,7 @@ more details, with real examples. In this example, EXTRA_CFLAGS will be assigned the value -O1 if the $(CC) version is less than 4.2. - cc-ifversion takes all the shell operators: + 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. @@ -507,7 +507,7 @@ The first step is to tell kbuild that a host program exists. This is done utilising the variable hostprogs-y. The second step is to add an explicit dependency to the executable. -This can be done in two ways. Either add the dependency in a rule, +This can be done in two ways. Either add the dependency in a rule, or utilise the variable $(always). Both possibilities are described in the following. @@ -524,7 +524,7 @@ Both possibilities are described in the following. Kbuild assumes in the above example that bin2hex is made from a single c-source file named bin2hex.c located in the same directory as the Makefile. - + --- 4.2 Composite Host Programs Host programs can be made up based on composite objects. @@ -535,7 +535,7 @@ Both possibilities are described in the following. Example: #scripts/lxdialog/Makefile - hostprogs-y := lxdialog + hostprogs-y := lxdialog lxdialog-objs := checklist.o lxdialog.o Objects with extension .o are compiled from the corresponding .c @@ -544,8 +544,8 @@ Both possibilities are described in the following. Finally, the two .o files are linked to the executable, lxdialog. Note: The syntax <executable>-y is not permitted for host-programs. ---- 4.3 Defining shared libraries - +--- 4.3 Defining shared libraries + Objects with extension .so are considered shared libraries, and will be compiled as position independent objects. Kbuild provides support for shared libraries, but the usage @@ -558,7 +558,7 @@ Both possibilities are described in the following. hostprogs-y := conf conf-objs := conf.o libkconfig.so libkconfig-objs := expr.o type.o - + Shared libraries always require a corresponding -objs line, and in the example above the shared library libkconfig is composed by the two objects expr.o and type.o. @@ -579,7 +579,7 @@ Both possibilities are described in the following. In the example above the executable is composed of the C++ file qconf.cc - identified by $(qconf-cxxobjs). - + If qconf is composed by a mixture of .c and .cc files, then an additional line can be used to identify this. @@ -588,7 +588,7 @@ Both possibilities are described in the following. hostprogs-y := qconf qconf-cxxobjs := qconf.o qconf-objs := check.o - + --- 4.5 Controlling compiler options for host programs When compiling host programs, it is possible to set specific flags. @@ -600,23 +600,23 @@ Both possibilities are described in the following. Example: #scripts/lxdialog/Makefile HOST_EXTRACFLAGS += -I/usr/include/ncurses - + To set specific flags for a single file the following construction is used: Example: #arch/ppc64/boot/Makefile HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE) - + It is also possible to specify additional options to the linker. - + Example: #scripts/kconfig/Makefile HOSTLOADLIBES_qconf := -L$(QTDIR)/lib When linking qconf, it will be passed the extra option "-L$(QTDIR)/lib". - + --- 4.6 When host programs are actually built Kbuild will only build host-programs when they are referenced @@ -631,7 +631,7 @@ Both possibilities are described in the following. $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist ( cd $(obj); ./gen-devlist ) < $< - The target $(obj)/devlist.h will not be built before + The target $(obj)/devlist.h will not be built before $(obj)/gen-devlist is updated. Note that references to the host programs in special rules must be prefixed with $(obj). @@ -650,7 +650,7 @@ Both possibilities are described in the following. --- 4.7 Using hostprogs-$(CONFIG_FOO) - A typcal pattern in a Kbuild file looks like this: + A typical pattern in a Kbuild file looks like this: Example: #scripts/Makefile @@ -682,7 +682,8 @@ When executing "make clean", the two files "devlist.h classlist.h" will be deleted. Kbuild will assume files to be in same relative directory as the Makefile except if an absolute path is specified (path starting with '/'). -To delete a directory hirachy use: +To delete a directory hierarchy use: + Example: #scripts/package/Makefile clean-dirs := $(objtree)/debian/ @@ -740,7 +741,7 @@ When kbuild executes, the following steps are followed (roughly): 5) Recursively descend down in all directories listed in init-* core* drivers-* net-* libs-* and build all targets. - The values of the above variables are expanded in arch/$(ARCH)/Makefile. -6) All object files are then linked and the resulting file vmlinux is +6) All object files are then linked and the resulting file vmlinux is located at the root of the obj tree. The very first objects linked are listed in head-y, assigned by arch/$(ARCH)/Makefile. @@ -762,7 +763,7 @@ When kbuild executes, the following steps are followed (roughly): LDFLAGS := -m elf_s390 Note: EXTRA_LDFLAGS and LDFLAGS_$@ can be used to further customise the flags used. See chapter 7. - + LDFLAGS_MODULE Options for $(LD) when linking modules LDFLAGS_MODULE is used to set specific flags for $(LD) when @@ -845,7 +846,7 @@ When kbuild executes, the following steps are followed (roughly): $(CFLAGS_MODULE) contains extra C compiler flags used to compile code for loadable kernel modules. - + --- 6.2 Add prerequisites to archprepare: The archprepare: rule is used to list prerequisites that need to be @@ -869,7 +870,7 @@ When kbuild executes, the following steps are followed (roughly): corresponding arch-specific section for modules; the module-building machinery is all architecture-independent. - + head-y, init-y, core-y, libs-y, drivers-y, net-y $(head-y) lists objects to be linked first in vmlinux. @@ -926,7 +927,7 @@ When kbuild executes, the following steps are followed (roughly): #arch/i386/Makefile define archhelp echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' - endef + endif When make is executed without arguments, the first goal encountered will be built. In the top level Makefile the first goal present @@ -938,7 +939,7 @@ When kbuild executes, the following steps are followed (roughly): Example: #arch/i386/Makefile - all: bzImage + all: bzImage When "make" is executed without arguments, bzImage will be built. @@ -961,7 +962,7 @@ When kbuild executes, the following steps are followed (roughly): 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 Kbuild provides a few macros that are useful when building a @@ -995,7 +996,7 @@ When kbuild executes, the following steps are followed (roughly): ld Link target. Often, LDFLAGS_$@ is used to set specific options to ld. - + objcopy Copy binary. Uses OBJCOPYFLAGS usually specified in arch/$(ARCH)/Makefile. @@ -1053,7 +1054,7 @@ When kbuild executes, the following steps are followed (roughly): BUILD arch/i386/boot/bzImage will be displayed with "make KBUILD_VERBOSE=0". - + --- 6.8 Preprocessing linker scripts @@ -1062,19 +1063,19 @@ When kbuild executes, the following steps are followed (roughly): The script is a preprocessed variant of the file vmlinux.lds.S located in the same directory. kbuild knows .lds files and includes a rule *lds.S -> *lds. - + Example: #arch/i386/kernel/Makefile always := vmlinux.lds - + #Makefile export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH) - - The assigment to $(always) is used to tell kbuild to build the + + The assignment to $(always) is used to tell kbuild to build the target vmlinux.lds. The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the 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 @@ -1180,3 +1181,5 @@ Language QA by Jan Engelhardt <jengelh@gmx.de> - Generating offset header files. - Add more variables to section 7? + + |