Gabe Black has submitted this change. (
https://gem5-review.googlesource.com/c/public/gem5/+/55587 )
Change subject: arch-x86: Use different tables for 64 bit prefixes in the
decoder.
......................................................................
arch-x86: Use different tables for 64 bit prefixes in the decoder.
There are instructions in 64 bit mode which have been turned into the
REX and VEX prefixes, and which should no longer behave as instructions.
When not in 64 bit mode however, those instructions still need to behave
properly.
We were handling that for the REX prefixes by explicitly checking if the
prefix we found was one of those, and then whether we were in 64 bit
mode or not. We were not handling the VEX prefixes at all, so those were
always acting as prefixes, even when not in 64 bit mode.
This change replaces the REX check and possible VEX check by having two
prefix tables, one for 64 bit mode, and one for otherwise. The REX and
VEX prefixes are simply left out of the non 64b it mode table, making an
explicit check for them unnecessary.
Change-Id: Ia2fc17074015e074d1f156177bd499d67da5411d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55587
Maintainer: Gabe Black <[email protected]>
Tested-by: kokoro <[email protected]>
Reviewed-by: Gabe Black <[email protected]>
---
M src/arch/x86/decoder.cc
M src/arch/x86/decoder.hh
M src/arch/x86/decoder_tables.cc
3 files changed, 57 insertions(+), 9 deletions(-)
Approvals:
Gabe Black: Looks good to me, approved; Looks good to me, approved
kokoro: Regressions pass
diff --git a/src/arch/x86/decoder.cc b/src/arch/x86/decoder.cc
index 4c79872..5d78c5f 100644
--- a/src/arch/x86/decoder.cc
+++ b/src/arch/x86/decoder.cc
@@ -181,11 +181,11 @@
Decoder::State
Decoder::doPrefixState(uint8_t nextByte)
{
- uint8_t prefix = Prefixes[nextByte];
+ // The REX and VEX prefixes only exist in 64 bit mode, so we use a
+ // different table for that.
+ const int table_idx = emi.mode.submode == SixtyFourBitMode ? 1 : 0;
+ const uint8_t prefix = Prefixes[table_idx][nextByte];
State nextState = PrefixState;
- // REX prefixes are only recognized in 64 bit mode.
- if (prefix == RexPrefix && emi.mode.submode != SixtyFourBitMode)
- prefix = 0;
if (prefix)
consumeByte();
switch(prefix) {
diff --git a/src/arch/x86/decoder.hh b/src/arch/x86/decoder.hh
index 1f7a7e4..38a5e10 100644
--- a/src/arch/x86/decoder.hh
+++ b/src/arch/x86/decoder.hh
@@ -59,7 +59,7 @@
// These are defined and documented in decoder_tables.cc
static const uint8_t SizeTypeToSize[3][10];
typedef const uint8_t ByteTable[256];
- static ByteTable Prefixes;
+ static ByteTable Prefixes[2];
static ByteTable UsesModRMOneByte;
static ByteTable UsesModRMTwoByte;
@@ -70,7 +70,6 @@
static ByteTable ImmediateTypeTwoByte;
static ByteTable ImmediateTypeThreeByte0F38;
static ByteTable ImmediateTypeThreeByte0F3A;
- static ByteTable ImmediateTypeVex[10];
static X86ISAInst::MicrocodeRom microcodeRom;
diff --git a/src/arch/x86/decoder_tables.cc b/src/arch/x86/decoder_tables.cc
index b1154e7..8deb63f 100644
--- a/src/arch/x86/decoder_tables.cc
+++ b/src/arch/x86/decoder_tables.cc
@@ -59,9 +59,30 @@
const uint8_t V2 = Vex2Prefix;
const uint8_t V3 = Vex3Prefix;
- //This table identifies whether a byte is a prefix, and if it is,
+ //These table identifies whether a byte is a prefix, and if it is,
//which prefix it is.
- const Decoder::ByteTable Decoder::Prefixes =
+ const Decoder::ByteTable Decoder::Prefixes[] =
+ {{ //LSB
+// MSB 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F
+/* 0*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* 1*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* 2*/ 0 , 0 , 0 , 0 , 0 , 0 , ES, 0 , 0 , 0 , 0 , 0 , 0 , 0 , CS, 0,
+/* 3*/ 0 , 0 , 0 , 0 , 0 , 0 , SS, 0 , 0 , 0 , 0 , 0 , 0 , 0 , DS, 0,
+/* 4*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 ,
+/* 5*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* 6*/ 0 , 0 , 0 , 0 , FS, GS, OO, AO, 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* 7*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* 8*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* 9*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* A*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* B*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* C*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* D*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* E*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
+/* F*/ LO, 0 , RN, RE, 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0
+ },
+
+ //This table is the same as the above, except used in 64 bit mode.
{ //LSB
// MSB 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F
/* 0*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
@@ -80,7 +101,7 @@
/* D*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
/* E*/ 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0,
/* F*/ LO, 0 , RN, RE, 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0
- };
+ }};
// These tables identify whether a particular opcode uses the ModRM
byte.
const Decoder::ByteTable Decoder::UsesModRMOneByte =
--
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: Ia2fc17074015e074d1f156177bd499d67da5411d
Gerrit-Change-Number: 55587
Gerrit-PatchSet: 12
Gerrit-Owner: Gabe Black <[email protected]>
Gerrit-Reviewer: Bradford Beckmann <[email protected]>
Gerrit-Reviewer: Gabe Black <[email protected]>
Gerrit-Reviewer: Matt Sinclair <[email protected]>
Gerrit-Reviewer: Matthew Poremba <[email protected]>
Gerrit-Reviewer: kokoro <[email protected]>
Gerrit-MessageType: merged
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