Commit-ID: 5b673a48c54594108aec368014efc7334743f06a Gitweb: http://git.kernel.org/tip/5b673a48c54594108aec368014efc7334743f06a Author: Borislav Petkov <bp@xxxxxxx> AuthorDate: Sat, 4 Apr 2015 16:40:45 +0200 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Wed, 6 May 2015 11:25:31 +0200 x86/alternatives: Document macros Add some text to the macro magic for future reference and against failing human memory. Requested-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/include/asm/alternative-asm.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h index bdf02ee..e7636ba 100644 --- a/arch/x86/include/asm/alternative-asm.h +++ b/arch/x86/include/asm/alternative-asm.h @@ -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 -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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