[PATCH] x86: correct and simplify NOP disassembly

[Jan Beulich]

It's not just REX.W which is ignored with opcode 0x90. The same goes for
REX.R and REX.X as well as empty REX. None of these are forms of
"xchg %eax,%eax" (which would mean zero-extending %eax to %rax), so they
also shouldn't be disassembled this way.

While there simplify things: A single hook function suffices, thus
making it unnecessary to keep two expressions in sync. And checking
ins->address_mode for mode_64bit also is unnecessary, as "rex" can be
non-zero only in that case anyway.

--- a/gas/testsuite/gas/i386/ilp32/rex.d
+++ b/gas/testsuite/gas/i386/ilp32/rex.d
@@ -2,46 +2,4 @@
 #objdump: -dw
 #name: x86-64 (ILP32) manual rex prefix use
 #notarget: x86_64-*-elf*
-
-.*: +file format .*
-
-Disassembly of section .text:
-
-0+ <_start>:
-[	 ]*[0-9a-f]+:[	 ]+40 0f ae 00[	 ]+rex fxsave[	 ]+\(%rax\)
-[	 ]*[0-9a-f]+:[	 ]+48 0f ae 00[	 ]+fxsave64[	 ]+\(%rax\)
-[	 ]*[0-9a-f]+:[	 ]+41 0f ae 00[	 ]+fxsave[	 ]+\(%r8\)
-[	 ]*[0-9a-f]+:[	 ]+49 0f ae 00[	 ]+fxsave64[	 ]+\(%r8\)
-[	 ]*[0-9a-f]+:[	 ]+42 0f ae 04 05 00 00 00 00[	 ]+fxsave[	 ]+(0x0)?\(,%r8(,1)?\)
-[	 ]*[0-9a-f]+:[	 ]+4a 0f ae 04 05 00 00 00 00[	 ]+fxsave64[	 ]+(0x0)?\(,%r8(,1)?\)
-[	 ]*[0-9a-f]+:[	 ]+43 0f ae 04 00[	 ]+fxsave[	 ]+\(%r8,%r8(,1)?\)
-[	 ]*[0-9a-f]+:[	 ]+4b 0f ae 04 00[	 ]+fxsave64[	 ]+\(%r8,%r8(,1)?\)
-[	 ]*[0-9a-f]+:[	 ]+48 03 04 00[	 ]+add[	 ]+\(%rax,%rax(,1)?\),%rax
-[	 ]*[0-9a-f]+:[	 ]+44 03 04 00[	 ]+add[	 ]+\(%rax,%rax(,1)?\),%r8d
-[	 ]*[0-9a-f]+:[	 ]+41 03 04 00[	 ]+add[	 ]+\(%r8,%rax(,1)?\),%eax
-[	 ]*[0-9a-f]+:[	 ]+42 03 04 00[	 ]+add[	 ]+\(%rax,%r8(,1)?\),%eax
-[	 ]*[0-9a-f]+:[	 ]+49 03 04 00[	 ]+add[	 ]+\(%r8,%rax(,1)?\),%rax
-[	 ]*[0-9a-f]+:[	 ]+46 03 04 00[	 ]+add[	 ]+\(%rax,%r8(,1)?\),%r8d
-[	 ]*[0-9a-f]+:[	 ]+45 03 04 00[	 ]+add[	 ]+\(%r8,%rax(,1)?\),%r8d
-[	 ]*[0-9a-f]+:[	 ]+4a 03 04 00[	 ]+add[	 ]+\(%rax,%r8(,1)?\),%rax
-[	 ]*[0-9a-f]+:[	 ]+41\s+rex\.B
-[	 ]*[0-9a-f]+:[	 ]+9b dd 30\s+fsave\s+\(%rax\)
-[	 ]*[0-9a-f]+:[	 ]+9b 41 dd 30\s+fsave\s+\(%r8\)
-[	 ]*[0-9a-f]+:[	 ]+40 c5 f9 28 00[	 ]+rex vmovapd \(%rax\),%xmm0
-[	 ]*[0-9a-f]+:[	 ]+40[	 ]+rex
-[	 ]*[0-9a-f]+:[	 ]+41[	 ]+rex.B
-[	 ]*[0-9a-f]+:[	 ]+42[	 ]+rex.X
-[	 ]*[0-9a-f]+:[	 ]+43[	 ]+rex.XB
-[	 ]*[0-9a-f]+:[	 ]+44[	 ]+rex.R
-[	 ]*[0-9a-f]+:[	 ]+45[	 ]+rex.RB
-[	 ]*[0-9a-f]+:[	 ]+46[	 ]+rex.RX
-[	 ]*[0-9a-f]+:[	 ]+47[	 ]+rex.RXB
-[	 ]*[0-9a-f]+:[	 ]+48[	 ]+rex.W
-[	 ]*[0-9a-f]+:[	 ]+49[	 ]+rex.WB
-[	 ]*[0-9a-f]+:[	 ]+4a[	 ]+rex.WX
-[	 ]*[0-9a-f]+:[	 ]+4b[	 ]+rex.WXB
-[	 ]*[0-9a-f]+:[	 ]+4c[	 ]+rex.WR
-[	 ]*[0-9a-f]+:[	 ]+4d[	 ]+rex.WRB
-[	 ]*[0-9a-f]+:[	 ]+4e[	 ]+rex.WRX
-[	 ]*[0-9a-f]+:[	 ]+4f[	 ]+rex.WRXB
-#pass
+#dump: ../rex.d
--- a/gas/testsuite/gas/i386/rex.d
+++ b/gas/testsuite/gas/i386/rex.d
@@ -23,6 +23,11 @@ Disassembly of section .text:
 [	 ]*[0-9a-f]+:[	 ]+46 03 04 00[	 ]+add[	 ]+\(%rax,%r8(,1)?\),%r8d
 [	 ]*[0-9a-f]+:[	 ]+45 03 04 00[	 ]+add[	 ]+\(%r8,%rax(,1)?\),%r8d
 [	 ]*[0-9a-f]+:[	 ]+4a 03 04 00[	 ]+add[	 ]+\(%rax,%r8(,1)?\),%rax
+[	 ]*[0-9a-f]+:[	 ]+40 90[	 ]+rex nop
+[	 ]*[0-9a-f]+:[	 ]+48 90[	 ]+rex\.W nop
+[	 ]*[0-9a-f]+:[	 ]+44 90[	 ]+rex\.R nop
+[	 ]*[0-9a-f]+:[	 ]+42 90[	 ]+rex\.X nop
+[	 ]*[0-9a-f]+:[	 ]+41 90[	 ]+xchg[	 ]+%eax,%r8d
 [	 ]*[0-9a-f]+:[	 ]+41\s+rex\.B
 [	 ]*[0-9a-f]+:[	 ]+9b dd 30\s+fsave\s+\(%rax\)
 [	 ]*[0-9a-f]+:[	 ]+9b 41 dd 30\s+fsave\s+\(%r8\)
--- a/gas/testsuite/gas/i386/rex.s
+++ b/gas/testsuite/gas/i386/rex.s
@@ -20,6 +20,12 @@ _start:
 	rex.b add	(%rax,%rax), %r8d
 	rex.x add	(%rax,%rax), %rax
 
+	rex nop
+	rex.w nop
+	rex.r nop
+	rex.x nop
+	rex.b nop
+
 	.byte 0x41,0x9b,0xdd,0x30
 	fsave (%r8)
 
--- a/opcodes/i386-dis.c
+++ b/opcodes/i386-dis.c
@@ -98,8 +98,7 @@ static void VPCOM_Fixup (instr_info *, i
 static void OP_0f07 (instr_info *, int, int);
 static void OP_Monitor (instr_info *, int, int);
 static void OP_Mwait (instr_info *, int, int);
-static void NOP_Fixup1 (instr_info *, int, int);
-static void NOP_Fixup2 (instr_info *, int, int);
+static void NOP_Fixup (instr_info *, int, int);
 static void OP_3DNowSuffix (instr_info *, int, int);
 static void CMP_Fixup (instr_info *, int, int);
 static void BadOp (instr_info *);
@@ -2913,9 +2912,9 @@ static const struct dis386 reg_table[][8
 static const struct dis386 prefix_table[][4] = {
   /* PREFIX_90 */
   {
-    { "xchgS", { { NOP_Fixup1, eAX_reg }, { NOP_Fixup2, eAX_reg } }, 0 },
+    { "xchgS", { { NOP_Fixup, 0 }, { NOP_Fixup, 1 } }, 0 },
     { "pause", { XX }, 0 },
-    { "xchgS", { { NOP_Fixup1, eAX_reg }, { NOP_Fixup2, eAX_reg } }, 0 },
+    { "xchgS", { { NOP_Fixup, 0 }, { NOP_Fixup, 1 } }, 0 },
     { NULL, { { NULL, 0 } }, PREFIX_IGNORED }
   },
 
@@ -12724,25 +12723,14 @@ OP_0f07 (instr_info *ins, int bytemode,
    32bit mode and "xchg %rax,%rax" in 64bit mode.  */
 
 static void
-NOP_Fixup1 (instr_info *ins, int bytemode, int sizeflag)
+NOP_Fixup (instr_info *ins, int opnd, int sizeflag)
 {
-  if ((ins->prefixes & PREFIX_DATA) != 0
-      || (ins->rex != 0
-	  && ins->rex != 0x48
-	  && ins->address_mode == mode_64bit))
-    OP_REG (ins, bytemode, sizeflag);
-  else
+  if ((ins->prefixes & PREFIX_DATA) == 0 && (ins->rex & REX_B) == 0)
     strcpy (ins->obuf, "nop");
-}
-
-static void
-NOP_Fixup2 (instr_info *ins, int bytemode, int sizeflag)
-{
-  if ((ins->prefixes & PREFIX_DATA) != 0
-      || (ins->rex != 0
-	  && ins->rex != 0x48
-	  && ins->address_mode == mode_64bit))
-    OP_IMREG (ins, bytemode, sizeflag);
+  else if (opnd == 0)
+    OP_REG (ins, eAX_reg, sizeflag);
+  else
+    OP_IMREG (ins, eAX_reg, sizeflag);
 }
 
 static const char *const Suffix3DNow[] = {