KVM: x86 emulator: convert DIV/IDIV to fastop
Since DIV and IDIV can generate exceptions, we need an additional output
parameter indicating whether an execption has occured. To avoid increasing
register pressure on i386, we use %rsi, which is already allocated for
the fastop code pointer.
Gleb: added comment about fop usage as exception indication.
Signed-off-by: Avi Kivity <avi.kivity@gmail.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 3a3542a..8404dc3 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -183,6 +183,7 @@
* src: rdx (in/out)
* src2: rcx (in)
* flags: rflags (in/out)
+ * ex: rsi (in:fastop pointer, out:zero if exception)
*
* Moreover, they are all exactly FASTOP_SIZE bytes long, so functions for
* different operand sizes can be reached by calculation, rather than a jump
@@ -470,7 +471,10 @@
#define FOPNOP() FOP_ALIGN FOP_RET
#define FOP1E(op, dst) \
- FOP_ALIGN #op " %" #dst " \n\t" FOP_RET
+ FOP_ALIGN "10: " #op " %" #dst " \n\t" FOP_RET
+
+#define FOP1EEX(op, dst) \
+ FOP1E(op, dst) _ASM_EXTABLE(10b, kvm_fastop_exception)
#define FASTOP1(op) \
FOP_START(op) \
@@ -489,6 +493,15 @@
ON64(FOP1E(op, rcx)) \
FOP_END
+/* 1-operand, using src2 (for MUL/DIV r/m), with exceptions */
+#define FASTOP1SRC2EX(op, name) \
+ FOP_START(name) \
+ FOP1EEX(op, cl) \
+ FOP1EEX(op, cx) \
+ FOP1EEX(op, ecx) \
+ ON64(FOP1EEX(op, rcx)) \
+ FOP_END
+
#define FOP2E(op, dst, src) \
FOP_ALIGN #op " %" #src ", %" #dst " \n\t" FOP_RET
@@ -533,6 +546,9 @@
/* Special case for SETcc - 1 instruction per cc */
#define FOP_SETCC(op) ".align 4; " #op " %al; ret \n\t"
+asm(".global kvm_fastop_exception \n"
+ "kvm_fastop_exception: xor %esi, %esi; ret");
+
FOP_START(setcc)
FOP_SETCC(seto)
FOP_SETCC(setno)
@@ -1007,6 +1023,8 @@
FASTOP1SRC2(mul, mul_ex);
FASTOP1SRC2(imul, imul_ex);
+FASTOP1SRC2EX(div, div_ex);
+FASTOP1SRC2EX(idiv, idiv_ex);
FASTOP3WCL(shld);
FASTOP3WCL(shrd);
@@ -2131,26 +2149,6 @@
return X86EMUL_CONTINUE;
}
-static int em_div_ex(struct x86_emulate_ctxt *ctxt)
-{
- u8 de = 0;
-
- emulate_1op_rax_rdx(ctxt, "div", de);
- if (de)
- return emulate_de(ctxt);
- return X86EMUL_CONTINUE;
-}
-
-static int em_idiv_ex(struct x86_emulate_ctxt *ctxt)
-{
- u8 de = 0;
-
- emulate_1op_rax_rdx(ctxt, "idiv", de);
- if (de)
- return emulate_de(ctxt);
- return X86EMUL_CONTINUE;
-}
-
static int em_grp45(struct x86_emulate_ctxt *ctxt)
{
int rc = X86EMUL_CONTINUE;
@@ -3734,8 +3732,8 @@
F(DstMem | SrcNone | Lock, em_neg),
F(DstXacc | Src2Mem, em_mul_ex),
F(DstXacc | Src2Mem, em_imul_ex),
- I(DstXacc | Src2Mem, em_div_ex),
- I(DstXacc | Src2Mem, em_idiv_ex),
+ F(DstXacc | Src2Mem, em_div_ex),
+ F(DstXacc | Src2Mem, em_idiv_ex),
};
static const struct opcode group4[] = {
@@ -4571,9 +4569,12 @@
if (!(ctxt->d & ByteOp))
fop += __ffs(ctxt->dst.bytes) * FASTOP_SIZE;
asm("push %[flags]; popf; call *%[fastop]; pushf; pop %[flags]\n"
- : "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags)
- : "c"(ctxt->src2.val), [fastop]"S"(fop));
+ : "+a"(ctxt->dst.val), "+d"(ctxt->src.val), [flags]"+D"(flags),
+ [fastop]"+S"(fop)
+ : "c"(ctxt->src2.val));
ctxt->eflags = (ctxt->eflags & ~EFLAGS_MASK) | (flags & EFLAGS_MASK);
+ if (!fop) /* exception is returned in fop variable */
+ return emulate_de(ctxt);
return X86EMUL_CONTINUE;
}