[tip:x86/alternatives] x86/alternatives: Add macro comments

tip-bot for Borislav Petkov
2019-01-16T11:58:24Z

Commit-ID: 1c1ed4731cc81942a5b25f284a85257573829b9e
Gitweb: https://git.kernel.org/tip/1c1ed4731cc81942a5b25f284a85257573829b9e
Author: Borislav Petkov <bp@suse.de>
AuthorDate: Mon, 10 Dec 2018 12:21:48 +0100
Committer: Borislav Petkov <bp@suse.de>
CommitDate: Wed, 16 Jan 2019 12:40:07 +0100

x86/alternatives: Add macro comments

... so that when one stares at the .s output, one can find her way
around the resulting asm magic.

With it, ALTERNATIVE looks like this now:

# ALT: oldnstr
661:
...
662:
# ALT: padding
.skip ...
663:
.pushsection .altinstructions,"a"

...

.popsection
.pushsection .altinstr_replacement, "ax"
# ALT: replacement 1
6641:
...
6651:
.popsection

Merge __OLDINSTR() into OLDINSTR(), while at it.

No functional changes.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: X86 ML <x86@kernel.org>
Link: https://lkml.kernel.org/r/20181211222326.14581-2-bp@alien8.de
---
arch/x86/include/asm/alternative.h | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 0660e14690c8..373e2baca6ce 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -94,13 +94,12 @@ static inline int alternatives_text_reserved(void *start, void *end)
#define alt_total_slen alt_end_marker"b-661b"
#define alt_rlen(num) e_replacement(num)"f-"b_replacement(num)"f"

-#define __OLDINSTR(oldinstr, num) \
+#define OLDINSTR(oldinstr, num) \
+ "# ALT: oldnstr\n" \
"661:\n\t" oldinstr "\n662:\n" \
+ "# ALT: padding\n" \
".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * " \
- "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"
-
-#define OLDINSTR(oldinstr, num) \
- __OLDINSTR(oldinstr, num) \
+ "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n" \
alt_end_marker ":\n"

/*
@@ -116,7 +115,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
* additionally longer than the first replacement alternative.
*/
#define OLDINSTR_2(oldinstr, num1, num2) \
+ "# ALT: oldinstr2\n" \
"661:\n\t" oldinstr "\n662:\n" \
+ "# ALT: padding2\n" \
".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \
"(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \
alt_end_marker ":\n"
@@ -129,8 +130,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
" .byte " alt_rlen(num) "\n" /* replacement len */ \
" .byte " alt_pad_len "\n" /* pad len */

-#define ALTINSTR_REPLACEMENT(newinstr, feature, num) /* replacement */ \
- b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
+#define ALTINSTR_REPLACEMENT(newinstr, feature, num) /* replacement */ \
+ "# ALT: replacement " #num "\n" \
+ b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n"

/* alternative assembly primitive: */
#define ALTERNATIVE(oldinstr, newinstr, feature) \