x86: Make alternative instruction pointers relative
This save a few bytes on x86-64 and means that future patches can
apply alternatives to unrelocated code.
Signed-off-by: Andy Lutomirski <luto@mit.edu>
Link: http://lkml.kernel.org/r/ff64a6b9a1a3860ca4a7b8b6dc7b4754f9491cd7.1310563276.git.luto@mit.edu
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a81f2d5..ddb207b 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -263,6 +263,7 @@
struct alt_instr *end)
{
struct alt_instr *a;
+ u8 *instr, *replacement;
u8 insnbuf[MAX_PATCH_LEN];
DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
@@ -276,25 +277,29 @@
* order.
*/
for (a = start; a < end; a++) {
- u8 *instr = a->instr;
+ instr = (u8 *)&a->instr_offset + a->instr_offset;
+ replacement = (u8 *)&a->repl_offset + a->repl_offset;
BUG_ON(a->replacementlen > a->instrlen);
BUG_ON(a->instrlen > sizeof(insnbuf));
BUG_ON(a->cpuid >= NCAPINTS*32);
if (!boot_cpu_has(a->cpuid))
continue;
+
+ memcpy(insnbuf, replacement, a->replacementlen);
+
+ /* 0xe8 is a relative jump; fix the offset. */
+ if (*insnbuf == 0xe8 && a->replacementlen == 5)
+ *(s32 *)(insnbuf + 1) += replacement - instr;
+
+ add_nops(insnbuf + a->replacementlen,
+ a->instrlen - a->replacementlen);
+
#ifdef CONFIG_X86_64
/* vsyscall code is not mapped yet. resolve it manually. */
if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) {
instr = __va(instr - (u8*)VSYSCALL_START + (u8*)__pa_symbol(&__vsyscall_0));
- DPRINTK("%s: vsyscall fixup: %p => %p\n",
- __func__, a->instr, instr);
}
#endif
- memcpy(insnbuf, a->replacement, a->replacementlen);
- if (*insnbuf == 0xe8 && a->replacementlen == 5)
- *(s32 *)(insnbuf + 1) += a->replacement - a->instr;
- add_nops(insnbuf + a->replacementlen,
- a->instrlen - a->replacementlen);
text_poke_early(instr, insnbuf, a->instrlen);
}
}