Commit c7bb349e authored by Sam Ravnborg's avatar Sam Ravnborg

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
......@@ -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.
......
......@@ -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)
......
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