KVM: x86 emulator: simplify rip relative decoding

rip relative decoding is relative to the instruction pointer of the next
instruction; by moving address adjustment until after decoding is complete,
we remove the need to determine the instruction size.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 5 insertions, 18 deletions

diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index c3a823174f3..20b604489c3 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -664,7 +664,7 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
 {
         struct decode_cache *c = &ctxt->decode;
         u8 sib;
-        int index_reg = 0, base_reg = 0, scale, rip_relative = 0;
+        int index_reg = 0, base_reg = 0, scale;
         int rc = 0;
 
         if (c->rex_prefix) {
@@ -754,7 +754,7 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
                                 c->modrm_ea += c->regs[index_reg] << scale;
                 } else if ((c->modrm_rm & 7) == 5 && c->modrm_mod == 0) {
                         if (ctxt->mode == X86EMUL_MODE_PROT64)
-                                rip_relative = 1;
+                                c->rip_relative = 1;
                 } else
                         c->modrm_ea += c->regs[c->modrm_rm];
                 switch (c->modrm_mod) {
@@ -770,22 +770,6 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
                         break;
                 }
         }
-        if (rip_relative) {
-                c->modrm_ea += c->eip;
-                switch (c->d & SrcMask) {
-                case SrcImmByte:
-                        c->modrm_ea += 1;
-                        break;
-                case SrcImm:
-                        if (c->d & ByteOp)
-                                c->modrm_ea += 1;
-                        else
-                                if (c->op_bytes == 8)
-                                        c->modrm_ea += 4;
-                                else
-                                        c->modrm_ea += c->op_bytes;
-                }
-        }
 done:
         return rc;
 }
@@ -1044,6 +1028,9 @@ done_prefixes:
                 break;
         }
 
+        if (c->rip_relative)
+                c->modrm_ea += c->eip;
+
 done:
         return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
 }