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x86/uaccess: Use XORL %0,%0 in __get_user_asm()

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XORL %0,%0 is equivalent to XORQ %0,%0 as both will zero the entire
register. Use XORL %0,%0 for all operand sizes to avoid REX prefix byte
when legacy registers are used and to avoid size prefix byte when 16bit
registers are used.

Zeroing the full register is OK in this use case.

As a result, the size of the .fixup section decreases by 20 bytes.

 [ bp: Massage commit message. ]

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20200827180904.96399-1-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2020-08-27 20:09:04 +02:00 • committed by Borislav Petkov
parent f75aef392f
commit 767ec7289e
1 changed files with 1 additions and 1 deletions
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2
arch/x86/include/asm/uaccess.h
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@ -343,7 +343,7 @@ do { \
"2:\n" \
".section .fixup,\"ax\"\n" \
"3: mov %[efault],%[errout]\n" \
" xor"itype" %[output],%[output]\n" \
" xorl %k[output],%k[output]\n" \
" jmp 2b\n" \
".previous\n" \
_ASM_EXTABLE_UA(1b, 3b) \