kbuild: introduce destination-y for exported headers
xtensa and arm have asked for a possibility to export headers and locate them in a specific directory when exported. Introduce destiantion-y to support this. This patch in additiona adds some limited documentation for the variables used for exported headers. Signed-off-by: Sam Ravnborg <sam@ravnborg.org> Cc: Oskar Schirmer <os@emlix.com> Cc: Mikael Starvik <mikael.starvik@axis.com>hifive-unleashed-5.1
Sam Ravnborg
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@ -40,10 +40,16 @@ This document describes the Linux kernel Makefiles.
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--- 6.7 Custom kbuild commands
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--- 6.8 Preprocessing linker scripts
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=== 7 Kbuild Variables
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=== 8 Makefile language
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=== 9 Credits
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=== 10 TODO
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=== 7 Kbuild syntax for exported headers
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--- 7.1 header-y
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--- 7.2 objhdr-y
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--- 7.3 destination-y
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--- 7.4 unifdef-y (deprecated)
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=== 8 Kbuild Variables
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=== 9 Makefile language
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=== 10 Credits
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=== 11 TODO
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=== 1 Overview
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@ -1143,8 +1149,69 @@ When kbuild executes, the following steps are followed (roughly):
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The kbuild infrastructure for *lds file are used in several
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architecture-specific files.
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=== 7 Kbuild syntax for exported headers
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=== 7 Kbuild Variables
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The kernel include a set of headers that is exported to userspace.
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Many headers can be exported as-is but other headers requires a
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minimal pre-processing before they are ready for user-space.
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The pre-processing does:
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- drop kernel specific annotations
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- drop include of compiler.h
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- drop all sections that is kernel internat (guarded by ifdef __KERNEL__)
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Each relevant directory contain a file name "Kbuild" which specify the
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headers to be exported.
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See subsequent chapter for the syntax of the Kbuild file.
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--- 7.1 header-y
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header-y specify header files to be exported.
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Example:
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#include/linux/Kbuild
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header-y += usb/
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header-y += aio_abi.h
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The convention is to list one file per line and
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preferably in alphabetic order.
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header-y also specify which subdirectories to visit.
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A subdirectory is identified by a trailing '/' which
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can be seen in the example above for the usb subdirectory.
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Subdirectories are visited before their parent directories.
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--- 7.2 objhdr-y
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objhdr-y specifies generated files to be exported.
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Generated files are special as they need to be looked
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up in another directory when doing 'make O=...' builds.
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Example:
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#include/linux/Kbuild
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objhdr-y += version.h
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--- 7.3 destination-y
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When an architecture have a set of exported headers that needs to be
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exported to a different directory destination-y is used.
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destination-y specify the destination directory for all exported
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headers in the file where it is present.
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Example:
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#arch/xtensa/platforms/s6105/include/platform/Kbuild
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destination-y := include/linux
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In the example above all exported headers in the Kbuild file
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will be located in the directory "include/linux" when exported.
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--- 7.4 unifdef-y (deprecated)
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unifdef-y is deprecated. A direct replacement is header-y.
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=== 8 Kbuild Variables
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The top Makefile exports the following variables:
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@ -1206,7 +1273,7 @@ The top Makefile exports the following variables:
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INSTALL_MOD_STRIP will used as the option(s) to the strip command.
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=== 8 Makefile language
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=== 9 Makefile language
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The kernel Makefiles are designed to be run with GNU Make. The Makefiles
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use only the documented features of GNU Make, but they do use many
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@ -1225,14 +1292,14 @@ time the left-hand side is used.
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There are some cases where "=" is appropriate. Usually, though, ":="
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is the right choice.
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=== 9 Credits
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=== 10 Credits
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Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net>
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Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
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Updates by Sam Ravnborg <sam@ravnborg.org>
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Language QA by Jan Engelhardt <jengelh@gmx.de>
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=== 10 TODO
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=== 11 TODO
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- Describe how kbuild supports shipped files with _shipped.
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- Generating offset header files.
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@ -14,6 +14,8 @@ _dst := $(if $(dst),$(dst),$(obj))
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kbuild-file := $(srctree)/$(obj)/Kbuild
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include $(kbuild-file)
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_dst := $(if $(destination-y),$(destination-y),$(_dst))
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include scripts/Kbuild.include
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install := $(INSTALL_HDR_PATH)/$(_dst)
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