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x86, alternative, doc: Add comment for applying alternatives order 

Some string operation functions may be patched twice, e.g. on enhanced REP MOVSB
/STOSB processors, memcpy is patched first by fast string alternative function,
then it is patched by enhanced REP MOVSB/STOSB alternative function.

Add comment for applying alternatives order to warn people who may change the
applying alternatives order for any reason.

[ Documentation-only patch ]

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-4-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Fenghua Yu 2011-05-17 15:29:12 -07:00 committed by H. Peter Anvin
parent 161ec53c70
commit 5097313363
1 changed files with 9 additions and 0 deletions
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9
arch/x86/kernel/alternative.c
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@ -210,6 +210,15 @@ void __init_or_module apply_alternatives(struct alt_instr *start,
u8 insnbuf[MAX_PATCH_LEN];
DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
/*
* The scan order should be from start to end. A later scanned
* alternative code can overwrite a previous scanned alternative code.
* Some kernel functions (e.g. memcpy, memset, etc) use this order to
* patch code.
*
* So be careful if you want to change the scan order to any other
* order.
*/
for (a = start; a < end; a++) {
u8 *instr = a->instr;
BUG_ON(a->replacementlen > a->instrlen);