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Diffstat (limited to 'Documentation/kbuild/makefiles.rst')
| -rw-r--r-- | Documentation/kbuild/makefiles.rst | 69 |
1 files changed, 31 insertions, 38 deletions
diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index b9b50553bfc5..0e0eb2c8da7d 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -28,7 +28,6 @@ This document describes the Linux kernel Makefiles. --- 4.3 Using C++ for host programs --- 4.4 Controlling compiler options for host programs --- 4.5 When host programs are actually built - --- 4.6 Using hostprogs-$(CONFIG_FOO) === 5 Kbuild clean infrastructure @@ -297,9 +296,19 @@ more details, with real examples. If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular) the corresponding obj- variable will be set, and kbuild will descend down in the ext2 directory. - Kbuild only uses this information to decide that it needs to visit - the directory, it is the Makefile in the subdirectory that - specifies what is modular and what is built-in. + + Kbuild uses this information not only to decide that it needs to visit + the directory, but also to decide whether or not to link objects from + the directory into vmlinux. + + When Kbuild descends into the directory with 'y', all built-in objects + from that directory are combined into the built-in.a, which will be + eventually linked into vmlinux. + + When Kbuild descends into the directory with 'm', in contrast, nothing + from that directory will be linked into vmlinux. If the Makefile in + that directory specifies obj-y, those objects will be left orphan. + It is very likely a bug of the Makefile or of dependencies in Kconfig. It is good practice to use a `CONFIG_` variable when assigning directory names. This allows kbuild to totally skip the directory if the @@ -585,11 +594,11 @@ compilation stage. Two steps are required in order to use a host executable. The first step is to tell kbuild that a host program exists. This is -done utilising the variable hostprogs-y. +done utilising the variable "hostprogs". 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, -or utilise the variable $(always). +or utilise the variable "always-y". Both possibilities are described in the following. 4.1 Simple Host Program @@ -602,7 +611,7 @@ Both possibilities are described in the following. Example:: - hostprogs-y := bin2hex + hostprogs := bin2hex 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 @@ -620,7 +629,7 @@ Both possibilities are described in the following. Example:: #scripts/lxdialog/Makefile - hostprogs-y := lxdialog + hostprogs := lxdialog lxdialog-objs := checklist.o lxdialog.o Objects with extension .o are compiled from the corresponding .c @@ -640,7 +649,7 @@ Both possibilities are described in the following. Example:: #scripts/kconfig/Makefile - hostprogs-y := qconf + hostprogs := qconf qconf-cxxobjs := qconf.o In the example above the executable is composed of the C++ file @@ -652,7 +661,7 @@ Both possibilities are described in the following. Example:: #scripts/kconfig/Makefile - hostprogs-y := qconf + hostprogs := qconf qconf-cxxobjs := qconf.o qconf-objs := check.o @@ -700,7 +709,7 @@ Both possibilities are described in the following. Example:: #drivers/pci/Makefile - hostprogs-y := gen-devlist + hostprogs := gen-devlist $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist ( cd $(obj); ./gen-devlist ) < $< @@ -708,47 +717,31 @@ Both possibilities are described in the following. $(obj)/gen-devlist is updated. Note that references to the host programs in special rules must be prefixed with $(obj). - (2) Use $(always) + (2) Use always-y When there is no suitable special rule, and the host program - shall be built when a makefile is entered, the $(always) + shall be built when a makefile is entered, the always-y variable shall be used. Example:: #scripts/lxdialog/Makefile - hostprogs-y := lxdialog - always := $(hostprogs-y) + hostprogs := lxdialog + always-y := $(hostprogs) This will tell kbuild to build lxdialog even if not referenced in any rule. -4.6 Using hostprogs-$(CONFIG_FOO) ---------------------------------- - - A typical pattern in a Kbuild file looks like this: - - Example:: - - #scripts/Makefile - hostprogs-$(CONFIG_KALLSYMS) += kallsyms - - Kbuild knows about both 'y' for built-in and 'm' for module. - So if a config symbol evaluates to 'm', kbuild will still build - the binary. In other words, Kbuild handles hostprogs-m exactly - like hostprogs-y. But only hostprogs-y is recommended to be used - when no CONFIG symbols are involved. - 5 Kbuild clean infrastructure ============================= "make clean" deletes most generated files in the obj tree where the kernel is compiled. This includes generated files such as host programs. -Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always), -$(extra-y) and $(targets). They are all deleted during "make clean". -Files matching the patterns "*.[oas]", "*.ko", plus some additional files -generated by kbuild are deleted all over the kernel src tree when -"make clean" is executed. +Kbuild knows targets listed in $(hostprogs), $(always-y), $(always-m), +$(always-), $(extra-y), $(extra-) and $(targets). They are all deleted +during "make clean". Files matching the patterns "*.[oas]", "*.ko", plus +some additional files generated by kbuild are deleted all over the kernel +source tree when "make clean" is executed. Additional files or directories can be specified in kbuild makefiles by use of $(clean-files). @@ -1259,12 +1252,12 @@ When kbuild executes, the following steps are followed (roughly): Example:: #arch/x86/kernel/Makefile - always := vmlinux.lds + extra-y := vmlinux.lds #Makefile export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH) - The assignment to $(always) is used to tell kbuild to build the + The assignment to extra-y 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. |