[PATCH] fix disassembly of spurious REX prefix before FWAIT

[Roland McGrath <mcgrathr at google dot com>]

The x86 disassembler has explicit logic to recognize prefixes before an
FWAIT instruction as applying to that instruction rather than to the next
instruction (into which the FWAIT might be subsumed for disassembly purposes).
But this is broken in the case of REX prefixes.  This patch fixes it and
does not introduce any regressions on x86_64-linux-gnu.

Ok for trunk?


Thanks,
Roland


gas/testsuite/
2012-10-22  Roland McGrath  <mcgrathr@google.com>

	* gas/i386/x86-64-prefix-fwait.s: New file.
	* gas/i386/x86-64-prefix-fwait.d: New file.
	* gas/i386/x86-64-prefix-fwait-intel.d: New file.
	* gas/i386/i386.exp: Run them.

opcodes/
2012-10-22  Roland McGrath  <mcgrathr@google.com>

	* i386-dis.c (ckprefix): When bailing out for fwait with prefixes,
	set rex_used to rex.


diff --git a/gas/testsuite/gas/i386/i386.exp b/gas/testsuite/gas/i386/i386.exp
index 4739752..ba431b6 100644
--- a/gas/testsuite/gas/i386/i386.exp
+++ b/gas/testsuite/gas/i386/i386.exp
@@ -480,6 +480,8 @@ if [expr ([istarget "i*86-*-*"] || [istarget
"x86_64-*-*"]) && [gas_64_check]] t
     run_dump_test "x86-64-rdseed-intel"
     run_dump_test "x86-64-prefetch"
     run_dump_test "x86-64-prefetch-intel"
+    run_dump_test "x86-64-prefix-fwait"
+    run_dump_test "x86-64-prefix-fwait-intel"

     if { ![istarget "*-*-aix*"]
       && ![istarget "*-*-beos*"]
diff --git a/gas/testsuite/gas/i386/x86-64-prefix-fwait-intel.d
b/gas/testsuite/gas/i386/x86-64-prefix-fwait-intel.d
new file mode 100644
index 0000000..5237654
--- /dev/null
+++ b/gas/testsuite/gas/i386/x86-64-prefix-fwait-intel.d
@@ -0,0 +1,13 @@
+#objdump: -dw -Mintel
+#name: x86-64 prefix before fwait (Intel disassembly)
+#source: x86-64-prefix-fwait.s
+
+.*: +file format .*
+
+Disassembly of section .text:
+
+0+ <foo>:
+\s*[a-f0-9]+:	41                   	rex\.B
+\s*[a-f0-9]+:	9b dd 30             	fsave  \[rax\]
+\s*[a-f0-9]+:	9b 41 dd 30          	fsave  \[r8\]
+#pass
diff --git a/gas/testsuite/gas/i386/x86-64-prefix-fwait.d
b/gas/testsuite/gas/i386/x86-64-prefix-fwait.d
new file mode 100644
index 0000000..047b090
--- /dev/null
+++ b/gas/testsuite/gas/i386/x86-64-prefix-fwait.d
@@ -0,0 +1,12 @@
+#objdump: -dw
+#name: x86-64 prefix before fwait
+
+.*: +file format .*
+
+Disassembly of section .text:
+
+0+ <foo>:
+\s*[a-f0-9]+:	41                   	rex\.B
+\s*[a-f0-9]+:	9b dd 30             	fsave  \(%rax\)
+\s*[a-f0-9]+:	9b 41 dd 30          	fsave  \(%r8\)
+#pass
diff --git a/gas/testsuite/gas/i386/x86-64-prefix-fwait.s
b/gas/testsuite/gas/i386/x86-64-prefix-fwait.s
new file mode 100644
index 0000000..40d1f0b
--- /dev/null
+++ b/gas/testsuite/gas/i386/x86-64-prefix-fwait.s
@@ -0,0 +1,7 @@
+.text
+foo:
+.byte 0x41,0x9b,0xdd,0x30
+.byte 0x9b,0x41,0xdd,0x30
+
+# Get a good alignment.
+ .p2align	4,0
diff --git a/opcodes/i386-dis.c b/opcodes/i386-dis.c
index 15c968a..f8e62aa 100644
--- a/opcodes/i386-dis.c
+++ b/opcodes/i386-dis.c
@@ -10756,6 +10756,9 @@ ckprefix (void)
 	    {
 	      prefixes |= PREFIX_FWAIT;
 	      codep++;
+	      /* This ensures that the previous REX prefixes are noticed
+		 as unused prefixes, as in the return case below.  */
+	      rex_used = rex;
 	      return 1;
 	    }
 	  prefixes = PREFIX_FWAIT;