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Commit c7bb349e authored by Sam Ravnborg's avatar Sam Ravnborg
Browse files

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: default avatarSam Ravnborg <sam@ravnborg.org>
Cc: Oskar Schirmer <os@emlix.com>
Cc: Mikael Starvik <mikael.starvik@axis.com>
parent 4774bb1c

Documentation/kbuild/makefiles.txt

+75 −8
Original line number Diff line number Diff line
@@ -40,10 +40,16 @@ This document describes the Linux kernel Makefiles. 
	   --- 6.7 Custom kbuild commands

	   --- 6.8 Preprocessing linker scripts



	=== 7 Kbuild Variables

	=== 8 Makefile language

	=== 9 Credits

	=== 10 TODO

	=== 7 Kbuild syntax for exported headers

		--- 7.1 header-y

		--- 7.2 objhdr-y

		--- 7.3 destination-y

		--- 7.4 unifdef-y (deprecated)



	=== 8 Kbuild Variables

	=== 9 Makefile language

	=== 10 Credits

	=== 11 TODO



=== 1 Overview
@@ -1143,8 +1149,69 @@ When kbuild executes, the following steps are followed (roughly): 
	The kbuild infrastructure for *lds file are used in several

	architecture-specific files.



=== 7 Kbuild syntax for exported headers



The kernel include a set of headers that is exported to userspace.

Many headers can be exported as-is but other headers requires  a

minimal pre-processing before they are ready for user-space.

The pre-processing does:

- drop kernel specific annotations

- drop include of compiler.h

- drop all sections that is kernel internat (guarded by ifdef __KERNEL__)



Each relevant directory contain a file name "Kbuild" which specify the

headers to be exported.

See subsequent chapter for the syntax of the Kbuild file.



	--- 7.1 header-y



	header-y specify header files to be exported.



		Example:

			#include/linux/Kbuild

			header-y += usb/

			header-y += aio_abi.h



	The convention is to list one file per line and

	preferably in alphabetic order.



	header-y also specify which subdirectories to visit.

	A subdirectory is identified by a trailing '/' which

	can be seen in the example above for the usb subdirectory.



	Subdirectories are visited before their parent directories.



	--- 7.2 objhdr-y



	objhdr-y specifies generated files to be exported.

	Generated files are special as they need to be looked

	up in another directory when doing 'make O=...' builds.



		Example:

			#include/linux/Kbuild

			objhdr-y += version.h



	--- 7.3 destination-y



	When an architecture have a set of exported headers that needs to be

	exported to a different directory destination-y is used.

	destination-y specify the destination directory for all exported

	headers in the file where it is present.



		Example:

			#arch/xtensa/platforms/s6105/include/platform/Kbuild

			destination-y := include/linux



	In the example above all exported headers in the Kbuild file

	will be located in the directory "include/linux" when exported.





	--- 7.4 unifdef-y (deprecated)



	unifdef-y is deprecated. A direct replacement is header-y.





=== 7 Kbuild Variables

=== 8 Kbuild Variables



The top Makefile exports the following variables:
@@ -1206,7 +1273,7 @@ The top Makefile exports the following variables: 
	INSTALL_MOD_STRIP will used as the option(s) to the strip command.





=== 8 Makefile language

=== 9 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
@@ -1225,14 +1292,14 @@ time the left-hand side is used. 
There are some cases where "=" is appropriate.  Usually, though, ":="

is the right choice.



=== 9 Credits

=== 10 Credits



Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net>

Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>

Updates by Sam Ravnborg <sam@ravnborg.org>

Language QA by Jan Engelhardt <jengelh@gmx.de>



=== 10 TODO

=== 11 TODO



- Describe how kbuild supports shipped files with _shipped.

- Generating offset header files.

scripts/Makefile.headersinst

+2 −0
Original line number Diff line number Diff line
@@ -14,6 +14,8 @@ _dst := $(if $(dst),$(dst),$(obj)) 
kbuild-file := $(srctree)/$(obj)/Kbuild

include $(kbuild-file)



_dst := $(if $(destination-y),$(destination-y),$(_dst))



include scripts/Kbuild.include



install       := $(INSTALL_HDR_PATH)/$(_dst)