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x86/word-at-a-time: Remove .fixup usage

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Rewrite load_unaligned_zeropad() to not require .fixup text.

This is easiest done using asm-goto-output, where we can stick a C
label in the exception table entry. The fallback version isn't nearly
so nice but should work.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20211110101326.141775772@infradead.org
This commit is contained in:
Peter Zijlstra 2021-11-10 11:01:23 +01:00
parent d5d797dcbd
commit b776078025
1 changed files with 48 additions and 20 deletions
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68
arch/x86/include/asm/word-at-a-time.h
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@ -77,30 +77,58 @@ static inline unsigned long find_zero(unsigned long mask)
* and the next page not being mapped, take the exception and
* return zeroes in the non-existing part.
*/
#ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
static inline unsigned long load_unaligned_zeropad(const void *addr)
{
unsigned long ret, dummy;
unsigned long offset, data;
unsigned long ret;
asm_volatile_goto(
"1: mov %[mem], %[ret]\n"
_ASM_EXTABLE(1b, %l[do_exception])
: [ret] "=r" (ret)
: [mem] "m" (*(unsigned long *)addr)
: : do_exception);
return ret;
do_exception:
offset = (unsigned long)addr & (sizeof(long) - 1);
addr = (void *)((unsigned long)addr & ~(sizeof(long) - 1));
data = *(unsigned long *)addr;
ret = data >> offset * 8;
asm(
"1:\tmov %2,%0\n"
"2:\n"
".section .fixup,\"ax\"\n"
"3:\t"
"lea %2,%1\n\t"
"and %3,%1\n\t"
"mov (%1),%0\n\t"
"leal %2,%%ecx\n\t"
"andl %4,%%ecx\n\t"
"shll $3,%%ecx\n\t"
"shr %%cl,%0\n\t"
"jmp 2b\n"
".previous\n"
_ASM_EXTABLE(1b, 3b)
:"=&r" (ret),"=&c" (dummy)
:"m" (*(unsigned long *)addr),
"i" (-sizeof(unsigned long)),
"i" (sizeof(unsigned long)-1));
return ret;
}
#else /* !CONFIG_CC_HAS_ASM_GOTO_OUTPUT */
static inline unsigned long load_unaligned_zeropad(const void *addr)
{
unsigned long offset, data;
unsigned long ret, err = 0;
asm( "1: mov %[mem], %[ret]\n"
"2:\n"
_ASM_EXTABLE_FAULT(1b, 2b)
: [ret] "=&r" (ret), "+a" (err)
: [mem] "m" (*(unsigned long *)addr));
if (unlikely(err)) {
offset = (unsigned long)addr & (sizeof(long) - 1);
addr = (void *)((unsigned long)addr & ~(sizeof(long) - 1));
data = *(unsigned long *)addr;
ret = data >> offset * 8;
}
return ret;
}
#endif /* CONFIG_CC_HAS_ASM_GOTO_OUTPUT */
#endif /* _ASM_WORD_AT_A_TIME_H */