Re: [PATCH] x86 emulator: Add 'push/pop sreg' instructions

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On 08/19/2009 07:11 AM, Mohammed Gamal wrote:

+static void emulate_push_sreg(struct x86_emulate_ctxt *ctxt, int seg)
+{
+	struct decode_cache *c =&ctxt->decode;
+	struct kvm_segment segment;
+	
+	if (ctxt->mode == X86EMUL_MODE_PROT64&&  (seg != VCPU_SREG_FS ||
+						   seg != VCPU_SREG_GS)) {
+		kvm_queue_exception(ctxt->vcpu, UD_VECTOR);
+		return;
+	}

It's better to check at the callsite, in case the opcode is ever reused for a new instruction. Or even better, add a new decode flag No64 so we can do this during the decode stage.

+
+static int emulate_pop_sreg(struct x86_emulate_ctxt *ctxt,
+			     struct x86_emulate_ops *ops, int seg)
+{
+	struct decode_cache *c =&ctxt->decode;
+	struct kvm_segment segment;
+	int rc;
+
+	if (ctxt->mode == X86EMUL_MODE_PROT64&&  (seg != VCPU_SREG_FS ||
+						    seg != VCPU_SREG_GS)) {
+		kvm_queue_exception(ctxt->vcpu, UD_VECTOR);
+		return -1;
+	}
+
+	kvm_x86_ops->get_segment(ctxt->vcpu,&segment, seg);
+	rc = emulate_pop(ctxt, ops,&segment.selector, c->op_bytes);
+	if (rc != 0)
+		return rc;
+	
+	rc = kvm_load_segment_descriptor(ctxt->vcpu, segment.selector, 1, seg);
+	return rc;
+}

Why do the ->get_segment() at all? pop into a temporary variable, and call kvm_load_segment_descriptor() with that.


--
error compiling committee.c: too many arguments to function

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