diff options
| author | Borislav Petkov <bp@suse.de> | 2015-04-04 16:40:45 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-05-06 11:25:31 +0200 |
| commit | 5b673a48c54594108aec368014efc7334743f06a (patch) | |
| tree | 746c6eb8c0bb62b897b74d5f724cef8f3b285c01 /arch/x86/include/asm | |
| parent | d9ee948d82203811a545ba26b0172fce4970d1dc (diff) | |
x86/alternatives: Document macros
Add some text to the macro magic for future reference and against
failing human memory.
Requested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav 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: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/include/asm')
| -rw-r--r-- | arch/x86/include/asm/alternative-asm.h | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h index bdf02eeee765..e7636bac7372 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 |