On Sat, Feb 09, 2013 at 11:31:49AM +0200, Avi Kivity wrote:
> 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.
>
> Signed-off-by: Avi Kivity <avi.kivity@xxxxxxxxx>
> ---
> arch/x86/kvm/emulate.c | 51 +++++++++++++++++++++++++-------------------------
> 1 file changed, 26 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 0f0c15e..89f56bb 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -180,6 +180,7 @@
> * src: rdx (in/out)
> * src2: rcx (in)
> * flags: rflags (in/out)
> + * ex: rsi (in:nonzero, out:zero if exception)
in:fastop pointer, or "code pointer" may be?
> *
> * Moreover, they are all exactly FASTOP_SIZE bytes long, so functions for
> * different operand sizes can be reached by calculation, rather than a jump
> @@ -467,7 +468,10 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *));
> #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) \
> @@ -486,6 +490,15 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *));
> 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
>
> @@ -530,6 +543,9 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *));
> /* 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)
> @@ -1001,6 +1017,8 @@ FASTOP2(test);
>
> FASTOP1SRC2(mul, mul_ex);
> FASTOP1SRC2(imul, imul_ex);
> +FASTOP1SRC2EX(div, div_ex);
> +FASTOP1SRC2EX(idiv, idiv_ex);
>
> FASTOP3WCL(shld);
> FASTOP3WCL(shrd);
> @@ -2116,26 +2134,6 @@ static int em_jmp_far(struct x86_emulate_ctxt *ctxt)
> 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;
> @@ -3700,8 +3698,8 @@ static const struct opcode group3[] = {
> 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[] = {
> @@ -4518,9 +4516,12 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *))
> 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)
Looks like this magic deserves at least a short comment :)
> + return emulate_de(ctxt);
> return X86EMUL_CONTINUE;
> }
>
> --
> 1.8.1.2
--
Gleb.
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