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| -rw-r--r-- | Documentation/kbuild/makefiles.rst | 183 |
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diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index b80257a03830..2a18aea7c043 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -29,31 +29,37 @@ This document describes the Linux kernel Makefiles. --- 4.4 Controlling compiler options for host programs --- 4.5 When host programs are actually built - === 5 Kbuild clean infrastructure - - === 6 Architecture Makefiles - --- 6.1 Set variables to tweak the build to the architecture - --- 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 - --- 6.11 Post-link pass - - === 7 Kbuild syntax for exported headers - --- 7.1 no-export-headers - --- 7.2 generic-y - --- 7.3 generated-y - --- 7.4 mandatory-y - - === 8 Kbuild Variables - === 9 Makefile language - === 10 Credits - === 11 TODO + === 5 Userspace Program support + --- 5.1 Simple Userspace Program + --- 5.2 Composite Userspace Programs + --- 5.3 Controlling compiler options for userspace programs + --- 5.4 When userspace programs are actually built + + === 6 Kbuild clean infrastructure + + === 7 Architecture Makefiles + --- 7.1 Set variables to tweak the build to the architecture + --- 7.2 Add prerequisites to archheaders: + --- 7.3 Add prerequisites to archprepare: + --- 7.4 List directories to visit when descending + --- 7.5 Architecture-specific boot images + --- 7.6 Building non-kbuild targets + --- 7.7 Commands useful for building a boot image + --- 7.8 Custom kbuild commands + --- 7.9 Preprocessing linker scripts + --- 7.10 Generic header files + --- 7.11 Post-link pass + + === 8 Kbuild syntax for exported headers + --- 8.1 no-export-headers + --- 8.2 generic-y + --- 8.3 generated-y + --- 8.4 mandatory-y + + === 9 Kbuild Variables + === 10 Makefile language + === 11 Credits + === 12 TODO 1 Overview ========== @@ -732,7 +738,88 @@ Both possibilities are described in the following. This will tell kbuild to build lxdialog even if not referenced in any rule. -5 Kbuild clean infrastructure +5 Userspace Program support +=========================== + +Just like host programs, Kbuild also supports building userspace executables +for the target architecture (i.e. the same architecture as you are building +the kernel for). + +The syntax is quite similar. The difference is to use "userprogs" instead of +"hostprogs". + +5.1 Simple Userspace Program +---------------------------- + + The following line tells kbuild that the program bpf-direct shall be + built for the target architecture. + + Example:: + + userprogs := bpf-direct + + Kbuild assumes in the above example that bpf-direct is made from a + single C source file named bpf-direct.c located in the same directory + as the Makefile. + +5.2 Composite Userspace Programs +-------------------------------- + + Userspace programs can be made up based on composite objects. + The syntax used to define composite objects for userspace programs is + similar to the syntax used for kernel objects. + $(<executable>-objs) lists all objects used to link the final + executable. + + Example:: + + #samples/seccomp/Makefile + userprogs := bpf-fancy + bpf-fancy-objs := bpf-fancy.o bpf-helper.o + + Objects with extension .o are compiled from the corresponding .c + files. In the above example, bpf-fancy.c is compiled to bpf-fancy.o + and bpf-helper.c is compiled to bpf-helper.o. + + Finally, the two .o files are linked to the executable, bpf-fancy. + Note: The syntax <executable>-y is not permitted for userspace programs. + +5.3 Controlling compiler options for userspace programs +------------------------------------------------------- + + When compiling userspace programs, it is possible to set specific flags. + The programs will always be compiled utilising $(CC) passed + the options specified in $(KBUILD_USERCFLAGS). + To set flags that will take effect for all userspace programs created + in that Makefile, use the variable userccflags. + + Example:: + + # samples/seccomp/Makefile + userccflags += -I usr/include + + To set specific flags for a single file the following construction + is used: + + Example:: + + bpf-helper-userccflags += -I user/include + + It is also possible to specify additional options to the linker. + + Example:: + + # net/bpfilter/Makefile + bpfilter_umh-userldflags += -static + + When linking bpfilter_umh, it will be passed the extra option -static. + +5.4 When userspace programs are actually built +---------------------------------------------- + + Same as "When host programs are actually built". + +6 Kbuild clean infrastructure ============================= "make clean" deletes most generated files in the obj tree where the kernel @@ -790,7 +877,7 @@ is not operational at that point. Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will be visited during "make clean". -6 Architecture Makefiles +7 Architecture Makefiles ======================== The top level Makefile sets up the environment and does the preparation, @@ -820,7 +907,7 @@ When kbuild executes, the following steps are followed (roughly): - Preparing initrd images and the like -6.1 Set variables to tweak the build to the architecture +7.1 Set variables to tweak the build to the architecture -------------------------------------------------------- LDFLAGS @@ -967,7 +1054,7 @@ When kbuild executes, the following steps are followed (roughly): KBUILD_VMLINUX_LIBS together specify all the object files used to link vmlinux. -6.2 Add prerequisites to archheaders +7.2 Add prerequisites to archheaders ------------------------------------ The archheaders: rule is used to generate header files that @@ -977,7 +1064,7 @@ When kbuild executes, the following steps are followed (roughly): architecture itself. -6.3 Add prerequisites to archprepare +7.3 Add prerequisites to archprepare ------------------------------------ The archprepare: rule is used to list prerequisites that need to be @@ -995,7 +1082,7 @@ When kbuild executes, the following steps are followed (roughly): generating offset header files. -6.4 List directories to visit when descending +7.4 List directories to visit when descending --------------------------------------------- An arch Makefile cooperates with the top Makefile to define variables @@ -1030,7 +1117,7 @@ When kbuild executes, the following steps are followed (roughly): drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ -6.5 Architecture-specific boot images +7.5 Architecture-specific boot images ------------------------------------- An arch Makefile specifies goals that take the vmlinux file, compress @@ -1085,7 +1172,7 @@ When kbuild executes, the following steps are followed (roughly): When "make" is executed without arguments, bzImage will be built. -6.6 Building non-kbuild targets +7.6 Building non-kbuild targets ------------------------------- extra-y @@ -1108,7 +1195,7 @@ 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.a. -6.7 Commands useful for building a boot image +7.7 Commands useful for building a boot image --------------------------------------------- Kbuild provides a few macros that are useful when building a @@ -1211,7 +1298,7 @@ When kbuild executes, the following steps are followed (roughly): targets += $(dtb-y) DTC_FLAGS ?= -p 1024 -6.8 Custom kbuild commands +7.8 Custom kbuild commands -------------------------- When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand @@ -1241,7 +1328,7 @@ When kbuild executes, the following steps are followed (roughly): will be displayed with "make KBUILD_VERBOSE=0". -6.9 Preprocessing linker scripts +7.9 Preprocessing linker scripts -------------------------------- When the vmlinux image is built, the linker script @@ -1274,7 +1361,7 @@ When kbuild executes, the following steps are followed (roughly): The kbuild infrastructure for `*lds` files is used in several architecture-specific files. -6.10 Generic header files +7.10 Generic header files ------------------------- The directory include/asm-generic contains the header files @@ -1283,7 +1370,7 @@ When kbuild executes, the following steps are followed (roughly): to list the file in the Kbuild file. See "7.2 generic-y" for further info on syntax etc. -6.11 Post-link pass +7.11 Post-link pass ------------------- If the file arch/xxx/Makefile.postlink exists, this makefile @@ -1299,7 +1386,7 @@ When kbuild executes, the following steps are followed (roughly): For example, powerpc uses this to check relocation sanity of the linked vmlinux file. -7 Kbuild syntax for exported headers +8 Kbuild syntax for exported headers ------------------------------------ The kernel includes a set of headers that is exported to userspace. @@ -1319,14 +1406,14 @@ A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and arch/<arch>/include/asm/ to list asm files coming from asm-generic. See subsequent chapter for the syntax of the Kbuild file. -7.1 no-export-headers +8.1 no-export-headers --------------------- no-export-headers is essentially used by include/uapi/linux/Kbuild to avoid exporting specific headers (e.g. kvm.h) on architectures that do not support it. It should be avoided as much as possible. -7.2 generic-y +8.2 generic-y ------------- If an architecture uses a verbatim copy of a header from @@ -1356,7 +1443,7 @@ See subsequent chapter for the syntax of the Kbuild file. #include <asm-generic/termios.h> -7.3 generated-y +8.3 generated-y --------------- If an architecture generates other header files alongside generic-y @@ -1370,7 +1457,7 @@ See subsequent chapter for the syntax of the Kbuild file. #arch/x86/include/asm/Kbuild generated-y += syscalls_32.h -7.4 mandatory-y +8.4 mandatory-y --------------- mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild @@ -1380,7 +1467,7 @@ See subsequent chapter for the syntax of the Kbuild file. in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate a wrapper of the asm-generic one. -8 Kbuild Variables +9 Kbuild Variables ================== The top Makefile exports the following variables: @@ -1438,8 +1525,8 @@ The top Makefile exports the following variables: command. -9 Makefile language -=================== +10 Makefile language +==================== The kernel Makefiles are designed to be run with GNU Make. The Makefiles use only the documented features of GNU Make, but they do use many @@ -1458,7 +1545,7 @@ time the left-hand side is used. There are some cases where "=" is appropriate. Usually, though, ":=" is the right choice. -10 Credits +11 Credits ========== - Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> @@ -1466,7 +1553,7 @@ is the right choice. - Updates by Sam Ravnborg <sam@ravnborg.org> - Language QA by Jan Engelhardt <jengelh@gmx.de> -11 TODO +12 TODO ======= - Describe how kbuild supports shipped files with _shipped. |