kernel: add common infrastructure for unaligned access
authorHarvey Harrison <>
Tue, 29 Apr 2008 08:03:27 +0000 (01:03 -0700)
committerLinus Torvalds <>
Tue, 29 Apr 2008 15:06:27 +0000 (08:06 -0700)
kernel: add common infrastructure for unaligned access

Create a linux/unaligned directory similar in spirit to the linux/byteorder
folder to hold generic implementations collected from various arches.

Currently there are five implementations:
1) packed_struct.h: C-struct based, from asm-generic/unaligned.h
2) le_byteshift.h: Open coded byte-swapping, heavily based on asm-arm
3) be_byteshift.h: Open coded byte-swapping, heavily based on asm-arm
4) memmove.h: taken from multiple implementations in tree
5) access_ok.h: taken from x86 and others, unaligned access is ok.

All of the new implementations checks for sizes not equal to 1,2,4,8
and will fail to link.

API additions:

get_unaligned_{le16|le32|le64|be16|be32|be64}(p) which is meant to replace
code of the form:
le16_to_cpu(get_unaligned((__le16 *)p));

put_unaligned_{le16|le32|le64|be16|be32|be64}(val, pointer) which is meant to
replace code of the form:
put_unaligned(cpu_to_le16(val), (__le16 *)p);

The headers that arches should include from their asm/unaligned.h:

access_ok.h : Wrappers of the byteswapping functions in asm/byteorder

Choose a particular implementation for little-endian access:
le_memmove.h (arch must be LE)
le_struct.h (arch must be LE)

Choose a particular implementation for big-endian access:
be_memmove.h (arch must be BE)
be_struct.h (arch must be BE)

After including as needed from the above, include unaligned/generic.h and
define your arch's get/put_unaligned as (for LE):

Signed-off-by: Harvey Harrison <>
Cc: <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
include/linux/unaligned/access_ok.h [new file with mode: 0644]
include/linux/unaligned/be_byteshift.h [new file with mode: 0644]
include/linux/unaligned/be_memmove.h [new file with mode: 0644]
include/linux/unaligned/be_struct.h [new file with mode: 0644]
include/linux/unaligned/generic.h [new file with mode: 0644]
include/linux/unaligned/le_byteshift.h [new file with mode: 0644]
include/linux/unaligned/le_memmove.h [new file with mode: 0644]
include/linux/unaligned/le_struct.h [new file with mode: 0644]
include/linux/unaligned/memmove.h [new file with mode: 0644]
include/linux/unaligned/packed_struct.h [new file with mode: 0644]