X86: Disassemble primary opcode map's group 2 ModRM.reg == 6 aliases correctly

The instructions are not documented in the Intel SDM but are documented
in the AMD APM as an alias to the group 2, ModRM.reg == 4 variant.

Both AMD and Intel CPUs execute the C[0-1] and D[0-3] instructions as
expected, i.e., like the /4 aliases:

  #include <stdio.h>

  int main(void)
  {
          int a = 2;

          printf ("a before: %d\n", a);

          asm volatile(".byte 0xd0,0xf0"          /* SHL %al */
                       : "+a" (a));

          printf("a after : %d\n", a);

          return 0;
  }

  $ ./a.out
  a before: 2
  a after : 4

7 files changed, 47 insertions, 6 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index d693b665326..a57b5d30905 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,10 @@
+2017-07-05  Borislav Petkov  <bp@suse.de>
+
+	* testsuite/gas/i386/opcode.s: Add tests for ModRM.reg == 6 variants.
+	* testsuite/gas/i386/opcode.d: ditto.
+	* testsuite/gas/i386/x86-64-opcode.s: Add x86_64 variants too.
+	* testsuite/gas/i386/x86-64-opcode.d: ditto.
+
 2017-07-04  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
 
         * config/tc-arm.c (arm_regs): Add MVFR2.
diff --git a/gas/testsuite/gas/i386/opcode.d b/gas/testsuite/gas/i386/opcode.d
index c7dc41076a4..b80a78cd4b6 100644
--- a/gas/testsuite/gas/i386/opcode.d
+++ b/gas/testsuite/gas/i386/opcode.d
@@ -603,4 +603,10 @@ Disassembly of section .text:
  +[a-f0-9]+:	f6 c9 01             	test   \$(0x)?0*1,%cl
  +[a-f0-9]+:	66 f7 c9 02 00       	test   \$(0x)?0*2,%cx
  +[a-f0-9]+:	f7 c9 04 00 00 00    	test   \$(0x)?0*4,%ecx
+ +[a-f0-9]+:	c0 f0 02             	shl    \$0x2,%al
+ +[a-f0-9]+:	c1 f0 01             	shl    \$0x1,%eax
+ +[a-f0-9]+:	d0 f0                	shl    %al
+ +[a-f0-9]+:	d1 f0                	shl    %eax
+ +[a-f0-9]+:	d2 f0                	shl    %cl,%al
+ +[a-f0-9]+:	d3 f0                	shl    %cl,%eax
 #pass
diff --git a/gas/testsuite/gas/i386/opcode.s b/gas/testsuite/gas/i386/opcode.s
index 64357b53b5b..db47446dfa9 100644
--- a/gas/testsuite/gas/i386/opcode.s
+++ b/gas/testsuite/gas/i386/opcode.s
@@ -604,3 +604,9 @@ foo:
 	.byte 0xf6, 0xc9, 0x01
 	.byte 0x66, 0xf7, 0xc9, 0x02, 0x00
 	.byte 0xf7, 0xc9, 0x04, 0x00, 0x00, 0x00
+	.byte 0xc0, 0xf0, 0x02
+	.byte 0xc1, 0xf0, 0x01
+	.byte 0xd0, 0xf0
+	.byte 0xd1, 0xf0
+	.byte 0xd2, 0xf0
+	.byte 0xd3, 0xf0
diff --git a/gas/testsuite/gas/i386/x86-64-opcode.d b/gas/testsuite/gas/i386/x86-64-opcode.d
index a6087e0c455..bfffb6e0ae0 100644
--- a/gas/testsuite/gas/i386/x86-64-opcode.d
+++ b/gas/testsuite/gas/i386/x86-64-opcode.d
@@ -305,4 +305,13 @@ Disassembly of section .text:
 [ 	]*[a-f0-9]+:	66 f7 c9 02 00       	test   \$(0x)?0*2,%cx
 [ 	]*[a-f0-9]+:	f7 c9 04 00 00 00    	test   \$(0x)?0*4,%ecx
 [ 	]*[a-f0-9]+:	48 f7 c9 08 00 00 00 	test   \$(0x)?0*8,%rcx
+[ 	]*[a-f0-9]+:	c0 f0 02             	shl    \$0x2,%al
+[ 	]*[a-f0-9]+:	c1 f0 01             	shl    \$0x1,%eax
+[ 	]*[a-f0-9]+:	48 c1 f0 01          	shl    \$0x1,%rax
+[ 	]*[a-f0-9]+:	d0 f0                	shl    %al
+[ 	]*[a-f0-9]+:	d1 f0                	shl    %eax
+[ 	]*[a-f0-9]+:	48 d1 f0             	shl    %rax
+[ 	]*[a-f0-9]+:	d2 f0                	shl    %cl,%al
+[ 	]*[a-f0-9]+:	d3 f0                	shl    %cl,%eax
+[ 	]*[a-f0-9]+:	48 d3 f0             	shl    %cl,%rax
 #pass
diff --git a/gas/testsuite/gas/i386/x86-64-opcode.s b/gas/testsuite/gas/i386/x86-64-opcode.s
index ffc8b9479be..5df5d13f781 100644
--- a/gas/testsuite/gas/i386/x86-64-opcode.s
+++ b/gas/testsuite/gas/i386/x86-64-opcode.s
@@ -432,3 +432,12 @@
 	.byte 0x66, 0xf7, 0xc9, 0x02, 0x00
 	.byte 0xf7, 0xc9, 0x04, 0x00, 0x00, 0x00
 	.byte 0x48, 0xf7, 0xc9, 0x08, 0x00, 0x00, 0x00
+	.byte 0xc0, 0xf0, 0x02
+	.byte 0xc1, 0xf0, 0x01
+	.byte 0x48, 0xc1, 0xf0, 0x01
+	.byte 0xd0, 0xf0
+	.byte 0xd1, 0xf0
+	.byte 0x48, 0xd1, 0xf0
+	.byte 0xd2, 0xf0
+	.byte 0xd3, 0xf0
+	.byte 0x48, 0xd3, 0xf0
diff --git a/opcodes/ChangeLog b/opcodes/ChangeLog
index 6c18442aec9..a076189c132 100644
--- a/opcodes/ChangeLog
+++ b/opcodes/ChangeLog
@@ -1,3 +1,7 @@
+2017-07-05  Borislav Petkov  <bp@suse.de>
+
+	* i386-dis.c: Enable ModRM.reg /6 aliases.
+
 2017-07-04  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
 
         * opcodes/arm-dis.c: Support MVFR2 in disassembly
diff --git a/opcodes/i386-dis.c b/opcodes/i386-dis.c
index 612e06ffb5e..e95311e1017 100644
--- a/opcodes/i386-dis.c
+++ b/opcodes/i386-dis.c
@@ -3441,7 +3441,7 @@ static const struct dis386 reg_table[][8] = {
     { "rcrA",	{ Eb, Ib }, 0 },
     { "shlA",	{ Eb, Ib }, 0 },
     { "shrA",	{ Eb, Ib }, 0 },
-    { Bad_Opcode },
+    { "shlA",	{ Eb, Ib }, 0 },
     { "sarA",	{ Eb, Ib }, 0 },
   },
   /* REG_C1 */
@@ -3452,7 +3452,7 @@ static const struct dis386 reg_table[][8] = {
     { "rcrQ",	{ Ev, Ib }, 0 },
     { "shlQ",	{ Ev, Ib }, 0 },
     { "shrQ",	{ Ev, Ib }, 0 },
-    { Bad_Opcode },
+    { "shlQ",	{ Ev, Ib }, 0 },
     { "sarQ",	{ Ev, Ib }, 0 },
   },
   /* REG_C6 */
@@ -3485,7 +3485,7 @@ static const struct dis386 reg_table[][8] = {
     { "rcrA",	{ Eb, I1 }, 0 },
     { "shlA",	{ Eb, I1 }, 0 },
     { "shrA",	{ Eb, I1 }, 0 },
-    { Bad_Opcode },
+    { "shlA",	{ Eb, I1 }, 0 },
     { "sarA",	{ Eb, I1 }, 0 },
   },
   /* REG_D1 */
@@ -3496,7 +3496,7 @@ static const struct dis386 reg_table[][8] = {
     { "rcrQ",	{ Ev, I1 }, 0 },
     { "shlQ",	{ Ev, I1 }, 0 },
     { "shrQ",	{ Ev, I1 }, 0 },
-    { Bad_Opcode },
+    { "shlQ",	{ Ev, I1 }, 0 },
     { "sarQ",	{ Ev, I1 }, 0 },
   },
   /* REG_D2 */
@@ -3507,7 +3507,7 @@ static const struct dis386 reg_table[][8] = {
     { "rcrA",	{ Eb, CL }, 0 },
     { "shlA",	{ Eb, CL }, 0 },
     { "shrA",	{ Eb, CL }, 0 },
-    { Bad_Opcode },
+    { "shlA",	{ Eb, CL }, 0 },
     { "sarA",	{ Eb, CL }, 0 },
   },
   /* REG_D3 */
@@ -3518,7 +3518,7 @@ static const struct dis386 reg_table[][8] = {
     { "rcrQ",	{ Ev, CL }, 0 },
     { "shlQ",	{ Ev, CL }, 0 },
     { "shrQ",	{ Ev, CL }, 0 },
-    { Bad_Opcode },
+    { "shlQ",	{ Ev, CL }, 0 },
     { "sarQ",	{ Ev, CL }, 0 },
   },
   /* REG_F6 */