Commit 50973133 authored May 17, 2011 by Fenghua Yu Committed by H. Peter Anvin May 17, 2011

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>

parent 161ec53c

arch/x86/kernel/alternative.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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);