On 07/28/2010 02:06 AM, Mohammed Gamal wrote:
Ths patch adds IRET instruction (opcode 0xcf).
Currently, only IRET in real mode is emulated. Protected mode support is to be added later if needed.
@@ -1778,6 +1778,69 @@ static int emulate_popa(struct x86_emulate_ctxt *ctxt,
return rc;
}
+static int emulate_iret_real(struct x86_emulate_ctxt *ctxt,
+ struct x86_emulate_ops *ops)
+{
+ struct decode_cache *c =&ctxt->decode;
+ int rc = X86EMUL_CONTINUE;
+ unsigned long temp_eip = 0;
+ unsigned long temp_eflags = 0;
+ unsigned long mask = EFLG_CF | EFLG_PF | EFLG_AF | EFLG_ZF | EFLG_SF | EFLG_TF |
+ EFLG_IF | EFLG_DF | EFLG_OF | EFLG_IOPL | EFLG_NT | EFLG_RF |
+ EFLG_AC | EFLG_ID | (1<< 1); /* Last one is the reserved bit */
+ unsigned long vm86_mask = EFLG_VM | EFLG_VIF | EFLG_VIP;
+
+ /* TODO: Add stack limit check */
+
+ rc = emulate_pop(ctxt, ops,&temp_eip, c->op_bytes);
+
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+
+ if (temp_eip& ~0xffff) {
+ emulate_gp(ctxt, 0);
+ return X86EMUL_PROPAGATE_FAULT;
+ }
+
+ c->eip = temp_eip;
+
+ rc = emulate_pop_sreg(ctxt, ops, VCPU_SREG_CS);
+
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+
+ rc = emulate_pop(ctxt, ops,&temp_eflags, c->op_bytes);
If this pop fails, the emulate_pop_sreg() will already have been
committed and the cs will be corrupted. That's a preexisting problem,
however, we can fix it later.
+
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+
+ if (c->op_bytes == 4) {
+ temp_eflags = ((temp_eflags& mask) | (ctxt->eflags& vm86_mask));
+ ctxt->eflags = temp_eflags;
Can combine to a single assignment instead of two.
+ } else if (c->op_bytes == 2) {
+ temp_eflags&= ~0xfffd; /* Do not clear reserved bit 1 */
+ ctxt->eflags |= temp_eflags;
If temp_eflags has CF clear, but ctxt->eflags has CF set, we end up with
CF set, incorrectly. Need to drop the low 16 bits from ctxt->eflags.
+ }
+
Need also to ensure reserved bits are set to their required values,
something like
ctxt->eflags &= ~EFLG_RESERVED_0_MASK; (0xffc0802a)
ctxt->eflags |= EFLG_RESERVERD_1_MASK; (0x2)
+ return rc;
+}
+
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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