[v2] x86emul: relax asm() constraints

Commit Message

Jan Beulich Feb. 16, 2016, 10:16 a.m. UTC

Let's give the compiler as much liberty at picking instruction operands
as possible. Also drop unnecessary size modifiers when the correct size
can already be derived from the asm() operands. Finally also drop an
"unsigned" from idiv_dbl()'s second parameter, allowing a cast to be
eliminated.

Signed-off-by: Jan Beulich <[e-mail]>
---
v2: Extend a couple of "=q" to "=qm" and one (in div_dbl()) "r" to "rm".
x86emul: relax asm() constraints

Let's give the compiler as much liberty at picking instruction operands
as possible. Also drop unnecessary size modifiers when the correct size
can already be derived from the asm() operands. Finally also drop an
"unsigned" from idiv_dbl()'s second parameter, allowing a cast to be
eliminated.

Signed-off-by: Jan Beulich <[e-mail]>
---
v2: Extend a couple of "=q" to "=qm" and one (in div_dbl()) "r" to "rm".

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -611,7 +611,7 @@ do {
  */
 static bool_t even_parity(uint8_t v)
 {
-    asm ( "test %b0,%b0; setp %b0" : "=a" (v) : "0" (v) );
+    asm ( "test %1,%1; setp %0" : "=qm" (v) : "q" (v) );
     return v;
 }
 
@@ -813,9 +813,9 @@ static int read_ulong(
  */
 static bool_t mul_dbl(unsigned long m[2])
 {
-    bool_t rc = 0;
-    asm ( "mul %1; seto %b2"
-          : "+a" (m[0]), "+d" (m[1]), "+q" (rc) );
+    bool_t rc;
+    asm ( "mul %1; seto %2"
+          : "+a" (m[0]), "+d" (m[1]), "=qm" (rc) );
     return rc;
 }
 
@@ -826,9 +826,9 @@ static bool_t mul_dbl(unsigned long m[2]
  */
 static bool_t imul_dbl(unsigned long m[2])
 {
-    bool_t rc = 0;
-    asm ( "imul %1; seto %b2"
-          : "+a" (m[0]), "+d" (m[1]), "+q" (rc) );
+    bool_t rc;
+    asm ( "imul %1; seto %2"
+          : "+a" (m[0]), "+d" (m[1]), "=qm" (rc) );
     return rc;
 }
 
@@ -842,7 +842,7 @@ static bool_t div_dbl(unsigned long u[2]
 {
     if ( (v == 0) || (u[1] >= v) )
         return 1;
-    asm ( "div %2" : "+a" (u[0]), "+d" (u[1]) : "r" (v) );
+    asm ( "divq %2" : "+a" (u[0]), "+d" (u[1]) : "rm" (v) );
     return 0;
 }
 
@@ -854,9 +854,9 @@ static bool_t div_dbl(unsigned long u[2]
  * NB. We don't use idiv directly as it's moderately hard to work out
  *     ahead of time whether it will #DE, which we cannot allow to happen.
  */
-static bool_t idiv_dbl(unsigned long u[2], unsigned long v)
+static bool_t idiv_dbl(unsigned long u[2], long v)
 {
-    bool_t negu = (long)u[1] < 0, negv = (long)v < 0;
+    bool_t negu = (long)u[1] < 0, negv = v < 0;
 
     /* u = abs(u) */
     if ( negu )
@@ -4542,9 +4542,10 @@ x86_emulate(
 
     case 0xbc: /* bsf or tzcnt */ {
         bool_t zf;
-        asm ( "bsf %2,%0; setz %b1"
-              : "=r" (dst.val), "=q" (zf)
-              : "r" (src.val) );
+
+        asm ( "bsf %2,%0; setz %1"
+              : "=r" (dst.val), "=qm" (zf)
+              : "rm" (src.val) );
         _regs.eflags &= ~EFLG_ZF;
         if ( (vex.pfx == vex_f3) && vcpu_has_bmi1() )
         {
@@ -4567,9 +4568,10 @@ x86_emulate(
 
     case 0xbd: /* bsr or lzcnt */ {
         bool_t zf;
-        asm ( "bsr %2,%0; setz %b1"
-              : "=r" (dst.val), "=q" (zf)
-              : "r" (src.val) );
+
+        asm ( "bsr %2,%0; setz %1"
+              : "=r" (dst.val), "=qm" (zf)
+              : "rm" (src.val) );
         _regs.eflags &= ~EFLG_ZF;
         if ( (vex.pfx == vex_f3) && vcpu_has_lzcnt() )
         {
@@ -4698,7 +4700,7 @@ x86_emulate(
             break;
         case 4:
 #ifdef __x86_64__
-            asm ( "bswap %k0" : "=r" (dst.val) : "0" (*dst.reg) );
+            asm ( "bswap %k0" : "=r" (dst.val) : "0" (*(uint32_t *)dst.reg) );
             break;
         case 8:
 #endif

Comments

Andrew Cooper Feb. 16, 2016, 11:14 a.m. UTC | #1

On 16/02/16 10:16, Jan Beulich wrote:
> Let's give the compiler as much liberty at picking instruction operands
> as possible. Also drop unnecessary size modifiers when the correct size
> can already be derived from the asm() operands. Finally also drop an
> "unsigned" from idiv_dbl()'s second parameter, allowing a cast to be
> eliminated.
>
> Signed-off-by: Jan Beulich <[e-mail]>

Reviewed-by: Andrew Cooper <[e-mail]>

Patch

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -611,7 +611,7 @@  do {
  */
 static bool_t even_parity(uint8_t v)
 {
-    asm ( "test %b0,%b0; setp %b0" : "=a" (v) : "0" (v) );
+    asm ( "test %1,%1; setp %0" : "=qm" (v) : "q" (v) );
     return v;
 }
 
@@ -813,9 +813,9 @@  static int read_ulong(
  */
 static bool_t mul_dbl(unsigned long m[2])
 {
-    bool_t rc = 0;
-    asm ( "mul %1; seto %b2"
-          : "+a" (m[0]), "+d" (m[1]), "+q" (rc) );
+    bool_t rc;
+    asm ( "mul %1; seto %2"
+          : "+a" (m[0]), "+d" (m[1]), "=qm" (rc) );
     return rc;
 }
 
@@ -826,9 +826,9 @@  static bool_t mul_dbl(unsigned long m[2]
  */
 static bool_t imul_dbl(unsigned long m[2])
 {
-    bool_t rc = 0;
-    asm ( "imul %1; seto %b2"
-          : "+a" (m[0]), "+d" (m[1]), "+q" (rc) );
+    bool_t rc;
+    asm ( "imul %1; seto %2"
+          : "+a" (m[0]), "+d" (m[1]), "=qm" (rc) );
     return rc;
 }
 
@@ -842,7 +842,7 @@  static bool_t div_dbl(unsigned long u[2]
 {
     if ( (v == 0) || (u[1] >= v) )
         return 1;
-    asm ( "div %2" : "+a" (u[0]), "+d" (u[1]) : "r" (v) );
+    asm ( "divq %2" : "+a" (u[0]), "+d" (u[1]) : "rm" (v) );
     return 0;
 }
 
@@ -854,9 +854,9 @@  static bool_t div_dbl(unsigned long u[2]
  * NB. We don't use idiv directly as it's moderately hard to work out
  *     ahead of time whether it will #DE, which we cannot allow to happen.
  */
-static bool_t idiv_dbl(unsigned long u[2], unsigned long v)
+static bool_t idiv_dbl(unsigned long u[2], long v)
 {
-    bool_t negu = (long)u[1] < 0, negv = (long)v < 0;
+    bool_t negu = (long)u[1] < 0, negv = v < 0;
 
     /* u = abs(u) */
     if ( negu )
@@ -4542,9 +4542,10 @@  x86_emulate(
 
     case 0xbc: /* bsf or tzcnt */ {
         bool_t zf;
-        asm ( "bsf %2,%0; setz %b1"
-              : "=r" (dst.val), "=q" (zf)
-              : "r" (src.val) );
+
+        asm ( "bsf %2,%0; setz %1"
+              : "=r" (dst.val), "=qm" (zf)
+              : "rm" (src.val) );
         _regs.eflags &= ~EFLG_ZF;
         if ( (vex.pfx == vex_f3) && vcpu_has_bmi1() )
         {
@@ -4567,9 +4568,10 @@  x86_emulate(
 
     case 0xbd: /* bsr or lzcnt */ {
         bool_t zf;
-        asm ( "bsr %2,%0; setz %b1"
-              : "=r" (dst.val), "=q" (zf)
-              : "r" (src.val) );
+
+        asm ( "bsr %2,%0; setz %1"
+              : "=r" (dst.val), "=qm" (zf)
+              : "rm" (src.val) );
         _regs.eflags &= ~EFLG_ZF;
         if ( (vex.pfx == vex_f3) && vcpu_has_lzcnt() )
         {
@@ -4698,7 +4700,7 @@  x86_emulate(
             break;
         case 4:
 #ifdef __x86_64__
-            asm ( "bswap %k0" : "=r" (dst.val) : "0" (*dst.reg) );
+            asm ( "bswap %k0" : "=r" (dst.val) : "0" (*(uint32_t *)dst.reg) );
             break;
         case 8:
 #endif