[4/5] i386: Add -mbranches-within-32B-boundaries

Message ID 20191112161905.10048-5-hjl.tools@gmail.com
State Superseded
Headers show
Series
  • i386: Optimize for Jump Conditional Code Erratum
Related show

Commit Message

H.J. Lu Nov. 12, 2019, 4:19 p.m.
Add -mbranches-within-32B-boundaries to enable

-malign-branch-boundary=32
-malign-branch=jcc+fused+jmp
-malign-branch-prefix-size=5

	* config/tc-i386.c (OPTION_MBRANCHES_WITH_32B_BOUNDARIES): New.
	(md_longopts): Add -mbranches-within-32B-boundaries.
	(md_parse_option): Handle -mbranches-within-32B-boundaries.
	(md_show_usage): Add -mbranches-within-32B-boundaries.
---
 gas/config/tc-i386.c | 13 +++++++++++++
 gas/doc/c-i386.texi  | 11 +++++++++++
 2 files changed, 24 insertions(+)

-- 
2.21.0

Patch

diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index cb96f8b348..52eb1c1a02 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -11897,6 +11897,7 @@  const char *md_shortopts = "qnO::";
 #define OPTION_MALIGN_BRANCH_BOUNDARY (OPTION_MD_BASE + 27)
 #define OPTION_MALIGN_BRANCH_PREFIX_SIZE (OPTION_MD_BASE + 28)
 #define OPTION_MALIGN_BRANCH (OPTION_MD_BASE + 29)
+#define OPTION_MBRANCHES_WITH_32B_BOUNDARIES (OPTION_MD_BASE + 30)
 
 struct option md_longopts[] =
 {
@@ -11935,6 +11936,7 @@  struct option md_longopts[] =
   {"malign-branch-boundary", required_argument, NULL, OPTION_MALIGN_BRANCH_BOUNDARY},
   {"malign-branch-prefix-size", required_argument, NULL, OPTION_MALIGN_BRANCH_PREFIX_SIZE},
   {"malign-branch", required_argument, NULL, OPTION_MALIGN_BRANCH},
+  {"mbranches-within-32B-boundaries", no_argument, NULL, OPTION_MBRANCHES_WITH_32B_BOUNDARIES},
   {"mamd64", no_argument, NULL, OPTION_MAMD64},
   {"mintel64", no_argument, NULL, OPTION_MINTEL64},
   {NULL, no_argument, NULL, 0}
@@ -12395,6 +12397,14 @@  md_parse_option (int c, const char *arg)
       free (saved);
       break;
 
+    case OPTION_MBRANCHES_WITH_32B_BOUNDARIES:
+      align_branch_power = 5;
+      align_branch_prefix_size = 5;
+      align_branch = (align_branch_jcc
+		      | align_branch_fused
+		      | align_branch_jmp);
+      break;
+
     case OPTION_MAMD64:
       intel64 = 0;
       break;
@@ -12658,6 +12668,9 @@  md_show_usage (FILE *stream)
   -malign-branch-prefix-size=NUM (default: 5)\n\
                           align branches with NUM prefixes per instruction\n"));
   fprintf (stream, _("\
+  -mbranches-within-32B-boundaries\n\
+                          align branches within 32 byte boundary\n"));
+  fprintf (stream, _("\
   -mamd64                 accept only AMD64 ISA [default]\n"));
   fprintf (stream, _("\
   -mintel64               accept only Intel64 ISA\n"));
diff --git a/gas/doc/c-i386.texi b/gas/doc/c-i386.texi
index 9b86ee3485..c2c655270b 100644
--- a/gas/doc/c-i386.texi
+++ b/gas/doc/c-i386.texi
@@ -449,6 +449,17 @@  This option specifies the maximum number of prefixes on an instruction
 to align branches.  @var{NUM} should be between 0 and 5.  The default
 @var{NUM} is 5.
 
+@cindex @samp{-mbranches-within-32B-boundaries} option, i386
+@cindex @samp{-mbranches-within-32B-boundaries} option, x86-64
+@item -mbranches-within-32B-boundaries
+This option aligns conditional jumps, fused conditional jumps and
+unconditional jumps within 32 byte boundary with up to 5 segment prefixes
+on an instruction.  It is equivalent to
+@option{-malign-branch-boundary=32}
+@option{-malign-branch=jcc+fused+jmp}
+@option{-malign-branch-prefix-size=5}.
+The default doesn't align branches.
+
 @cindex @samp{-mx86-used-note=} option, i386
 @cindex @samp{-mx86-used-note=} option, x86-64
 @item -mx86-used-note=@var{no}