[PATCH 20/22] x86,word-at-a-time: Remove .fixup usage

Peter Zijlstra
2021-11-05T17:20:49Z

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>
---
arch/x86/include/asm/word-at-a-time.h | 67 ++++++++++++++++++++++++----------
1 file changed, 48 insertions(+), 19 deletions(-)

--- a/arch/x86/include/asm/word-at-a-time.h
+++ b/arch/x86/include/asm/word-at-a-time.h
@@ -77,30 +77,59 @@ static inline unsigned long find_zero(un
* 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 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);
+
+out:
+ return ret;
+
+do_exception: __cold;
+
+ offset = (unsigned long)addr & (sizeof(long) - 1);
+ addr = (void *)((unsigned long)addr & ~(sizeof(long) - 1));
+ data = *(unsigned long *)addr;
+ ret = data >> offset * 8;
+ goto out;
+}
+
+#else /* !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, err = 0;

- asm(
- "1:\tmov %2,%0\n"
+ asm( "1: mov %[mem], %[ret]\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));
+
+ _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 */