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0652035a57
In theory, compilers should be able to work this out themselves so we can use a simpler version based on the swab() helpers. I have verified that this works on all supported compiler versions (gcc-4.9 and up, clang-10 and up). Looking at the object code produced by gcc-11, I found that the impact is mostly a change in inlining decisions that lead to slightly larger code. In other cases, this version produces explicit byte swaps in place of separate byte access, or comparing against pre-swapped constants. While the source code is clearly simpler, I have not seen an indication of the new version actually producing better code on Arm, so maybe we want to skip this after all. From what I can tell, gcc recognizes the byteswap pattern in the byteshift.h header and can turn it into explicit instructions, but it does not turn a __builtin_bswap32() back into individual bytes when that would result in better output, e.g. when storing a byte-reversed constant. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
25 lines
760 B
C
25 lines
760 B
C
#ifndef __ASM_ARM_UNALIGNED_H
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#define __ASM_ARM_UNALIGNED_H
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/*
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* We generally want to set CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS on ARMv6+,
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* but we don't want to use linux/unaligned/access_ok.h since that can lead
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* to traps on unaligned stm/ldm or strd/ldrd.
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*/
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#include <asm/byteorder.h>
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#if defined(__LITTLE_ENDIAN)
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# include <linux/unaligned/le_struct.h>
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# include <linux/unaligned/generic.h>
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# define get_unaligned __get_unaligned_le
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# define put_unaligned __put_unaligned_le
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#elif defined(__BIG_ENDIAN)
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# include <linux/unaligned/be_struct.h>
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# include <linux/unaligned/generic.h>
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# define get_unaligned __get_unaligned_be
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# define put_unaligned __put_unaligned_be
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#else
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# error need to define endianess
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#endif
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#endif /* __ASM_ARM_UNALIGNED_H */
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