linux-kernel - [RFC PATCH 1/4] x86/alternatives: Add macro comments

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Message-Id: <20181211222326.14581-2-bp@alien8.de>
Date:   Tue, 11 Dec 2018 23:23:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     X86 ML <x86@...nel.org>, Andy Lutomirski <luto@...capital.net>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [RFC PATCH 1/4] x86/alternatives: Add macro comments

From: Borislav Petkov <bp@...e.de>

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

For example, 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@...e.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 d7faa16622d8..8d38b296a18a 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -87,13 +87,12 @@ 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"
 
 /*
@@ -109,7 +108,9 @@ 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"
@@ -122,8 +123,9 @@ 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)			\
-- 
2.19.1