Xen devel - Feb 2008 - [PATCH] x86_emulate: fix side-effect macro call

x86_emulate: fix side-effect macro call
Both jmp_rel and insn_fetch_type increment eip, so it''s not
compiler-safe to nest the calls.

Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>

---
Yes, I actually got a bug because of this, with debian''s gcc 4.2.3.

diff -r 52f222b319ef xen/arch/x86/x86_emulate.c
--- a/xen/arch/x86/x86_emulate.c	Tue Feb 05 11:21:22 2008 +0000
+++ b/xen/arch/x86/x86_emulate.c	Tue Feb 05 15:30:48 2008 +0000
@@ -2644,9 +2644,11 @@
         break;
     }
 
-    case 0xeb: /* jmp (short) */
-        jmp_rel(insn_fetch_type(int8_t));
+    case 0xeb: /* jmp (short) */ {
+        int8_t rel = insn_fetch_type(int8_t);
+        jmp_rel(rel);
         break;
+    }
 
     case 0xf1: /* int1 (icebp) */
         src.val = EXC_DB;

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Samuel Thibault, le Tue 05 Feb 2008 15:33:55 +0000, a écrit
:
> x86_emulate: fix side-effect macro call
> Both jmp_rel and insn_fetch_type increment eip, so it''s not
> compiler-safe to nest the calls.
Another way to fix it would be to change jmp_rel:

- _regs.eip += (int)(rel);
+ int _rel = (int)(rel);
+ _regs.eip += _rel;

Samuel

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