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Commit 5b673a48 authored by Borislav Petkov's avatar Borislav Petkov Committed by Ingo Molnar
Browse files

x86/alternatives: Document macros 



Add some text to the macro magic for future reference and against
failing human memory.

Requested-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent d9ee948d

arch/x86/include/asm/alternative-asm.h

+18 −0
Original line number Diff line number Diff line
@@ -18,6 +18,12 @@ 
	.endm

#endif



/*

 * Issue one struct alt_instr descriptor entry (need to put it into

 * the section .altinstructions, see below). This entry contains

 * enough information for the alternatives patching code to patch an

 * instruction. See apply_alternatives().

 */

.macro altinstruction_entry orig alt feature orig_len alt_len pad_len

	.long \orig - .

	.long \alt - .
@@ -27,6 +33,12 @@ 
	.byte \pad_len

.endm



/*

 * Define an alternative between two instructions. If @feature is

 * present, early code in apply_alternatives() replaces @oldinstr with

 * @newinstr. ".skip" directive takes care of proper instruction padding

 * in case @newinstr is longer than @oldinstr.

 */

.macro ALTERNATIVE oldinstr, newinstr, feature

140:

	\oldinstr
@@ -55,6 +67,12 @@ 
 */

#define alt_max_short(a, b)	((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))





/*

 * Same as ALTERNATIVE macro above but for two alternatives. If CPU

 * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has

 * @feature2, it replaces @oldinstr with @feature2.

 */

.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2

140:

	\oldinstr