Add -momit_lock_prefix=[no|yes] option

This option serves as a workaround for processors, which fail on lock
prefix.

gas/
	* config/tc-i386.c (omit_lock_prefix): New.
	(output_insn): Omit lock prefix if omit_lock_prefix is true.
	(OPTION_omit_lock_prefix): New.
	(md_longopts): Add momit-lock-prefix.
	(md_parse_option): Handle momit-lock-prefix.
	(md_show_usage): Add momit-lock-prefix=[no|yes].
	* doc/c-i386.texi (momit-lock-prefix): Document.

gas/testsuite/

	* gas/i386/i386.exp: Run new tests.
	* gas/i386/omit-lock-no.d: New.
	* gas/i386/omit-lock-yes.d: Ditto.
	* gas/i386/omit-lock.s: Ditto.

8 files changed, 88 insertions, 0 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index b7926f4..2a584fd 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,13 @@
+2014-08-06  Ilya Tocar  <ilya.tocar@intel.com>
+
+	* config/tc-i386.c (omit_lock_prefix): New.
+	(output_insn): Omit lock prefix if omit_lock_prefix is true.
+	(OPTION_omit_lock_prefix): New.
+	(md_longopts): Add momit-lock-prefix.
+	(md_parse_option): Handle momit-lock-prefix.
+	(md_show_usage): Add momit-lock-prefix=[no|yes].
+	* doc/c-i386.texi (momit-lock-prefix): Document.
+
 2014-08-01  Takashi Yoshii  <yoshii.takashi@renesas.com>
 
 	PR 10378
diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index c61d22b..ab5a319 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -543,6 +543,10 @@ static int add_bnd_prefix = 0;
 /* 1 if pseudo index register, eiz/riz, is allowed .  */
 static int allow_index_reg = 0;
 
+/* 1 if the assembler should ignore LOCK prefix, even if it was
+   specified explicitly.  */
+static int omit_lock_prefix = 0;
+
 static enum check_kind
   {
     check_none = 0,
@@ -6938,6 +6942,15 @@ output_insn (void)
       unsigned int j;
       unsigned int prefix;
 
+      /* Some processors fail on LOCK prefix. This options makes
+	 assembler ignore LOCK prefix and serves as a workaround.  */
+      if (omit_lock_prefix)
+	{
+	  if (i.tm.base_opcode == LOCK_PREFIX_OPCODE)
+	    return;
+	  i.prefix[LOCK_PREFIX] = 0;
+	}
+
       /* Since the VEX/EVEX prefix contains the implicit prefix, we
 	 don't need the explicit prefix.  */
       if (!i.tm.opcode_modifier.vex && !i.tm.opcode_modifier.evex)
@@ -9532,6 +9545,7 @@ const char *md_shortopts = "qn";
 #define OPTION_MEVEXLIG (OPTION_MD_BASE + 16)
 #define OPTION_MEVEXWIG (OPTION_MD_BASE + 17)
 #define OPTION_MBIG_OBJ (OPTION_MD_BASE + 18)
+#define OPTION_omit_lock_prefix (OPTION_MD_BASE + 19)
 
 struct option md_longopts[] =
 {
@@ -9561,6 +9575,7 @@ struct option md_longopts[] =
 # if defined (TE_PE) || defined (TE_PEP)
   {"mbig-obj", no_argument, NULL, OPTION_MBIG_OBJ},
 #endif
+  {"momit-lock-prefix", required_argument, NULL, OPTION_omit_lock_prefix},
   {NULL, no_argument, NULL, 0}
 };
 size_t md_longopts_size = sizeof (md_longopts);
@@ -9848,6 +9863,15 @@ md_parse_option (int c, char *arg)
       break;
 #endif
 
+    case OPTION_omit_lock_prefix:
+      if (strcasecmp (arg, "yes") == 0)
+        omit_lock_prefix = 1;
+      else if (strcasecmp (arg, "no") == 0)
+        omit_lock_prefix = 0;
+      else
+        as_fatal (_("invalid -momit-lock-prefix= option: `%s'"), arg);
+      break;
+
     default:
       return 0;
     }
@@ -10004,6 +10028,9 @@ md_show_usage (FILE *stream)
   fprintf (stream, _("\
   -mbig-obj               generate big object files\n"));
 #endif
+  fprintf (stream, _("\
+  -momit-lock-prefix=[no|yes]\n\
+                          strip all lock prefixes\n"));
 }
 
 #if ((defined (OBJ_MAYBE_COFF) && defined (OBJ_MAYBE_AOUT)) \
diff --git a/gas/doc/c-i386.texi b/gas/doc/c-i386.texi
index c1631c2..0c2e134 100644
--- a/gas/doc/c-i386.texi
+++ b/gas/doc/c-i386.texi
@@ -291,6 +291,18 @@ if such prefix was not explicitly specified in the source code.
 On x86-64 PE/COFF target this option forces the use of big object file
 format, which allows more than 32768 sections.
 
+@cindex @samp{-momit-lock-prefix=} option, i386
+@cindex @samp{-momit-lock-prefix=} option, x86-64
+@item -momit-lock-prefix=@var{no}
+@itemx -momit-lock-prefix=@var{yes}
+These options control how the assembler should encode lock prefix.
+This option is intended as a workaround for processors, that fail on
+lock prefix. This option can only be safely used with single-core,
+single-thread computers
+@option{-momit-lock-prefix=@var{yes}} will omit all lock prefixes.
+@option{-momit-lock-prefix=@var{no}} will encode lock prefix as usual,
+which is the default.
+
 @end table
 @c man end
 
diff --git a/gas/testsuite/ChangeLog b/gas/testsuite/ChangeLog
index acb0ac2..44e3c34 100644
--- a/gas/testsuite/ChangeLog
+++ b/gas/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2014-08-06  Ilya Tocar  <ilya.tocar@intel.com>
+
+	* gas/i386/i386.exp: Run new tests.
+	* gas/i386/omit-lock-no.d: New.
+	* gas/i386/omit-lock-yes.d: Ditto.
+	* gas/i386/omit-lock.s: Ditto.
+
 2014-07-29  Matthew Fortune  <matthew.fortune@imgtec.com>
 
 	* gas/mips/attr-gnu-4-0.d: New.
diff --git a/gas/testsuite/gas/i386/i386.exp b/gas/testsuite/gas/i386/i386.exp
index 01de5d9..680d28c 100644
--- a/gas/testsuite/gas/i386/i386.exp
+++ b/gas/testsuite/gas/i386/i386.exp
@@ -301,6 +301,8 @@ if [expr ([istarget "i*86-*-*"] ||  [istarget "x86_64-*-*"]) && [gas_32_check]]
     run_dump_test "avx512dq"
     run_dump_test "avx512dq_vl-intel"
     run_dump_test "avx512dq_vl"
+    run_dump_test "omit-lock-yes"
+    run_dump_test "omit-lock-no"
     run_dump_test "disassem"
 
     # These tests require support for 8 and 16 bit relocs,
diff --git a/gas/testsuite/gas/i386/omit-lock-no.d b/gas/testsuite/gas/i386/omit-lock-no.d
new file mode 100644
index 0000000..87f796f
--- /dev/null
+++ b/gas/testsuite/gas/i386/omit-lock-no.d
@@ -0,0 +1,12 @@
+#source: omit-lock.s
+#as: -momit-lock-prefix=yes  -momit-lock-prefix=no
+#objdump: -dw
+#name: i386  omit lock = no
+
+.*: +file format .*i386.*
+
+Disassembly of section .text:
+
+0+ <main>:
+   0:	f0 f0 83 00 01       	lock lock addl \$0x1,\(%eax\)
+#pass
diff --git a/gas/testsuite/gas/i386/omit-lock-yes.d b/gas/testsuite/gas/i386/omit-lock-yes.d
new file mode 100644
index 0000000..67f0ef1
--- /dev/null
+++ b/gas/testsuite/gas/i386/omit-lock-yes.d
@@ -0,0 +1,12 @@
+#source: omit-lock.s
+#as: -momit-lock-prefix=yes
+#objdump: -dw
+#name: i386  omit lock = yes
+
+.*: +file format .*i386.*
+
+Disassembly of section .text:
+
+0+ <main>:
+   0:	83 00 01             	addl   \$0x1,\(%eax\)
+#pass
diff --git a/gas/testsuite/gas/i386/omit-lock.s b/gas/testsuite/gas/i386/omit-lock.s
new file mode 100644
index 0000000..b267ebe
--- /dev/null
+++ b/gas/testsuite/gas/i386/omit-lock.s
@@ -0,0 +1,6 @@
+        .code32
+.globl main
+        .type   main, @function
+main:
+	lock
+        lock addl $0x1,(%eax)