kbuild: doc: replace arch/$(ARCH)/ with arch/$(SRCARCH)/
Precisely speaking, the arch directory is specified by $(SRCARCH),
not $(ARCH).
In old days, $(ARCH) actually matched to the arch directory because
32-bit and 64-bit were supported as separate architectures.
Most architectures (except arm/arm64) were unified like follows:
arch/i386, arch/x86_64 -> arch/x86
arch/sh, arch/sh64 -> arch/sh
arch/sparc, arch/sparc64 -> arch/sparc
To not break the user interface, commit 6752ed90da ("Kbuild: allow
arch/xxx to use a different source path") introduced SRCARCH to point
to the arch directory, still allowing to pass in the former ARCH=i386
or ARCH=x86_64.
Update the documents for preciseness, and add the explanation of SRCARCH.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
This commit is contained in:
Masahiro Yamada
parent
b044a535d9
commit
8c4d9b145b
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@ -67,11 +67,11 @@ This document describes the Linux kernel Makefiles.
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The Makefiles have five parts::
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Makefile the top Makefile.
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.config the kernel configuration file.
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arch/$(ARCH)/Makefile the arch Makefile.
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scripts/Makefile.* common rules etc. for all kbuild Makefiles.
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kbuild Makefiles exist in every subdirectory
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Makefile the top Makefile.
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.config the kernel configuration file.
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arch/$(SRCARCH)/Makefile the arch Makefile.
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scripts/Makefile.* common rules etc. for all kbuild Makefiles.
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kbuild Makefiles exist in every subdirectory
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The top Makefile reads the .config file, which comes from the kernel
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configuration process.
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@ -82,7 +82,7 @@ It builds these goals by recursively descending into the subdirectories of
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the kernel source tree.
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The list of subdirectories which are visited depends upon the kernel
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configuration. The top Makefile textually includes an arch Makefile
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with the name arch/$(ARCH)/Makefile. The arch Makefile supplies
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with the name arch/$(SRCARCH)/Makefile. The arch Makefile supplies
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architecture-specific information to the top Makefile.
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Each subdirectory has a kbuild Makefile which carries out the commands
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@ -933,7 +933,7 @@ When "make clean" is executed, make will descend down in arch/x86/boot,
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and clean as usual. The Makefile located in arch/x86/boot/ may use
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the subdir- trick to descend further down.
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Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is
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Note 1: arch/$(SRCARCH)/Makefile cannot use "subdir-", because that file is
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included in the top level makefile, and the kbuild infrastructure
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is not operational at that point.
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@ -946,9 +946,9 @@ be visited during "make clean".
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The top level Makefile sets up the environment and does the preparation,
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before starting to descend down in the individual directories.
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The top level makefile contains the generic part, whereas
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arch/$(ARCH)/Makefile contains what is required to set up kbuild
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arch/$(SRCARCH)/Makefile contains what is required to set up kbuild
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for said architecture.
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To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines
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To do so, arch/$(SRCARCH)/Makefile sets up a number of variables and defines
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a few targets.
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When kbuild executes, the following steps are followed (roughly):
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@ -956,14 +956,14 @@ When kbuild executes, the following steps are followed (roughly):
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1) Configuration of the kernel => produce .config
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2) Store kernel version in include/linux/version.h
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3) Updating all other prerequisites to the target prepare:
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- Additional prerequisites are specified in arch/$(ARCH)/Makefile
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- Additional prerequisites are specified in arch/$(SRCARCH)/Makefile
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4) Recursively descend down in all directories listed in
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init-* core* drivers-* net-* libs-* and build all targets.
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- The values of the above variables are expanded in arch/$(ARCH)/Makefile.
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- The values of the above variables are expanded in arch/$(SRCARCH)/Makefile.
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5) All object files are then linked and the resulting file vmlinux is
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located at the root of the obj tree.
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The very first objects linked are listed in head-y, assigned by
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arch/$(ARCH)/Makefile.
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arch/$(SRCARCH)/Makefile.
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6) Finally, the architecture-specific part does any required post processing
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and builds the final bootimage.
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- This includes building boot records
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@ -1169,7 +1169,7 @@ When kbuild executes, the following steps are followed (roughly):
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$(core-y), $(libs-y), $(drivers-y) and $(net-y).
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The top level Makefile defines values for all generic directories,
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and arch/$(ARCH)/Makefile only adds architecture-specific
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and arch/$(SRCARCH)/Makefile only adds architecture-specific
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directories.
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Example::
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@ -1189,15 +1189,15 @@ When kbuild executes, the following steps are followed (roughly):
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The actual goals are not standardized across architectures.
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It is common to locate any additional processing in a boot/
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directory below arch/$(ARCH)/.
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directory below arch/$(SRCARCH)/.
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Kbuild does not provide any smart way to support building a
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target specified in boot/. Therefore arch/$(ARCH)/Makefile shall
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target specified in boot/. Therefore arch/$(SRCARCH)/Makefile shall
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call make manually to build a target in boot/.
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The recommended approach is to include shortcuts in
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arch/$(ARCH)/Makefile, and use the full path when calling down
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into the arch/$(ARCH)/boot/Makefile.
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arch/$(SRCARCH)/Makefile, and use the full path when calling down
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into the arch/$(SRCARCH)/boot/Makefile.
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Example::
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@ -1217,7 +1217,7 @@ When kbuild executes, the following steps are followed (roughly):
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#arch/x86/Makefile
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define archhelp
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echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)'
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echo '* bzImage - Compressed kernel image (arch/x86/boot/bzImage)'
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endif
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When make is executed without arguments, the first goal encountered
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@ -1332,7 +1332,7 @@ When kbuild executes, the following steps are followed (roughly):
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objcopy
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Copy binary. Uses OBJCOPYFLAGS usually specified in
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arch/$(ARCH)/Makefile.
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arch/$(SRCARCH)/Makefile.
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OBJCOPYFLAGS_$@ may be used to set additional options.
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gzip
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@ -1395,7 +1395,7 @@ When kbuild executes, the following steps are followed (roughly):
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--------------------------------
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When the vmlinux image is built, the linker script
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arch/$(ARCH)/kernel/vmlinux.lds is used.
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arch/$(SRCARCH)/kernel/vmlinux.lds is used.
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The script is a preprocessed variant of the file vmlinux.lds.S
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located in the same directory.
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kbuild knows .lds files and includes a rule `*lds.S` -> `*lds`.
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@ -1405,9 +1405,6 @@ When kbuild executes, the following steps are followed (roughly):
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#arch/x86/kernel/Makefile
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extra-y := vmlinux.lds
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#Makefile
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export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
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The assignment to extra-y is used to tell kbuild to build the
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target vmlinux.lds.
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The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the
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@ -1481,7 +1478,7 @@ See subsequent chapter for the syntax of the Kbuild file.
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If an architecture uses a verbatim copy of a header from
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include/asm-generic then this is listed in the file
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arch/$(ARCH)/include/asm/Kbuild like this:
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arch/$(SRCARCH)/include/asm/Kbuild like this:
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Example::
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@ -1492,7 +1489,7 @@ See subsequent chapter for the syntax of the Kbuild file.
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During the prepare phase of the build a wrapper include
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file is generated in the directory::
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arch/$(ARCH)/include/generated/asm
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arch/$(SRCARCH)/include/generated/asm
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When a header is exported where the architecture uses
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the generic header a similar wrapper is generated as part
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@ -1527,8 +1524,8 @@ See subsequent chapter for the syntax of the Kbuild file.
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to define the minimum set of ASM headers that all architectures must have.
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This works like optional generic-y. If a mandatory header is missing
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in arch/$(ARCH)/include/(uapi/)/asm, Kbuild will automatically generate
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a wrapper of the asm-generic one.
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in arch/$(SRCARCH)/include/(uapi/)/asm, Kbuild will automatically
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generate a wrapper of the asm-generic one.
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9 Kbuild Variables
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==================
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@ -1564,6 +1561,16 @@ The top Makefile exports the following variables:
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make ARCH=m68k ...
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SRCARCH
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This variable specifies the directory in arch/ to build.
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ARCH and SRCARCH may not necessarily match. A couple of arch
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directories are biarch, that is, a single `arch/*/` directory supports
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both 32-bit and 64-bit.
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For example, you can pass in ARCH=i386, ARCH=x86_64, or ARCH=x86.
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For all of them, SRCARCH=x86 because arch/x86/ supports both i386 and
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x86_64.
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INSTALL_PATH
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This variable defines a place for the arch Makefiles to install
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@ -332,7 +332,7 @@ according to the following rule:
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There are two notable exceptions to this rule: larger
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subsystems have their own directory under include/, such as
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include/scsi; and architecture specific headers are located
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under arch/$(ARCH)/include/.
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under arch/$(SRCARCH)/include/.
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4.1 Kernel Includes
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-------------------
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