x86/entry: Use 32bit xors rater than 64bit xors for clearing GPRs

Intel's Silvermont/Knights Landing architecture treats them as full ALU
operations, rather than zeroing idoms.

No functional change, and no change in code volume (only changing the bit
selection in the REX prefix).

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/include/asm-x86/asm_defns.h b/xen/include/asm-x86/asm_defns.h
index aee14ba007c6733d3c6ab0c94fea779e25972cc3..6fc13d39d8910f7a5981b70f3eb05e60da37ca62 100644 (file)
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -269,10 +269,10 @@ static always_inline void stac(void)
         movq  %r10,UREGS_r10(%rsp)
         movq  %r11,UREGS_r11(%rsp)
 .endif
-        xor   %r8, %r8
-        xor   %r9, %r9
-        xor   %r10, %r10
-        xor   %r11, %r11
+        xor   %r8d, %r8d
+        xor   %r9d, %r9d
+        xor   %r10d, %r10d
+        xor   %r11d, %r11d
         movq  %rbx,UREGS_rbx(%rsp)
         xor   %ebx, %ebx
         movq  %rbp,UREGS_rbp(%rsp)
@@ -289,10 +289,10 @@ static always_inline void stac(void)
         movq  %r14,UREGS_r14(%rsp)
         movq  %r15,UREGS_r15(%rsp)
 .endif
-        xor   %r12, %r12
-        xor   %r13, %r13
-        xor   %r14, %r14
-        xor   %r15, %r15
+        xor   %r12d, %r12d
+        xor   %r13d, %r13d
+        xor   %r14d, %r14d
+        xor   %r15d, %r15d
 .endm
 
 #define LOAD_ONE_REG(reg, compat) \
@@ -317,10 +317,10 @@ static always_inline void stac(void)
         movq  UREGS_r13(%rsp), %r13
         movq  UREGS_r12(%rsp), %r12
 .else
-        xor %r15, %r15
-        xor %r14, %r14
-        xor %r13, %r13
-        xor %r12, %r12
+        xor %r15d, %r15d
+        xor %r14d, %r14d
+        xor %r13d, %r13d
+        xor %r12d, %r12d
 .endif
         LOAD_ONE_REG(bp, \compat)
         LOAD_ONE_REG(bx, \compat)
@@ -330,10 +330,10 @@ static always_inline void stac(void)
         movq  UREGS_r9(%rsp),%r9
         movq  UREGS_r8(%rsp),%r8
 .else
-        xor %r11, %r11
-        xor %r10, %r10
-        xor %r9, %r9
-        xor %r8, %r8
+        xor %r11d, %r11d
+        xor %r10d, %r10d
+        xor %r9d, %r9d
+        xor %r8d, %r8d
 .endif
         LOAD_ONE_REG(ax, \compat)
         LOAD_ONE_REG(cx, \compat)