[PATCH 46/50] KVM: x86 emulator: simplify rip relative decoding

From: Avi Kivity
Date: Thu Jun 26 2008 - 08:37:32 EST


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@xxxxxxxxxxxx>
---
arch/x86/kvm/x86_emulate.c | 23 +++++------------------
include/asm-x86/kvm_x86_emulate.h | 1 +
2 files changed, 6 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index c3a8231..20b6044 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;
}
diff --git a/include/asm-x86/kvm_x86_emulate.h b/include/asm-x86/kvm_x86_emulate.h
index b877bbd..9fda4b3 100644
--- a/include/asm-x86/kvm_x86_emulate.h
+++ b/include/asm-x86/kvm_x86_emulate.h
@@ -134,6 +134,7 @@ struct decode_cache {
u8 modrm_reg;
u8 modrm_rm;
u8 use_modrm_ea;
+ bool rip_relative;
unsigned long modrm_ea;
void *modrm_ptr;
unsigned long modrm_val;
--
1.5.6

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