[gem5-dev] Change in gem5/gem5[develop]: arch-x86: Expose the current CPL to the decoder.

[Gabe Black (Gerrit) via gem5-dev]

Gabe Black has uploaded this change for review. (  
https://gem5-review.googlesource.com/c/public/gem5/+/55889 )

Change subject: arch-x86: Expose the current CPL to the decoder.
......................................................................

arch-x86: Expose the current CPL to the decoder.

This value is already floating around, and there is essentially no
overhead for exposing it to the decoder. With that value, we can handle
instructions which generically need to run at CPL0.

Some instructions have other more complicated permissions checks, like
that the CPL needs to have some relation to the IOPL. Those checks will
have to be implemented by the instructions themselves, since the decoder
can't factor in all possible state values.

Change-Id: Ie93f4f13aae002f69330606c515f369c5706c655
---
M src/arch/x86/decoder.hh
M src/arch/x86/isa/bitfields.isa
M src/arch/x86/types.hh
3 files changed, 33 insertions(+), 1 deletion(-)



diff --git a/src/arch/x86/decoder.hh b/src/arch/x86/decoder.hh
index 38a5e10..29415ef 100644
--- a/src/arch/x86/decoder.hh
+++ b/src/arch/x86/decoder.hh
@@ -110,6 +110,8 @@
     uint8_t defAddr = 0;
     uint8_t stack = 0;

+    uint8_t cpl = 0;
+
     uint8_t
     getNextByte()
     {
@@ -256,6 +258,7 @@
     Decoder(const X86DecoderParams &p) : InstDecoder(p, &fetchChunk)
     {
         emi.reset();
+        emi.mode.cpl = cpl;
         emi.mode.mode = mode;
         emi.mode.submode = submode;
     }
@@ -263,8 +266,10 @@
     void
     setM5Reg(HandyM5Reg m5Reg)
     {
+        cpl = m5Reg.cpl;
         mode = (X86Mode)(uint64_t)m5Reg.mode;
         submode = (X86SubMode)(uint64_t)m5Reg.submode;
+        emi.mode.cpl = cpl;
         emi.mode.mode = mode;
         emi.mode.submode = submode;
         altOp = m5Reg.altOp;
@@ -298,8 +303,10 @@
         Decoder *dec = dynamic_cast<Decoder *>(old);
         assert(dec);

+        cpl = dec->cpl;
         mode = dec->mode;
         submode = dec->submode;
+        emi.mode.cpl = cpl;
         emi.mode.mode = mode;
         emi.mode.submode = submode;
         altOp = dec->altOp;
diff --git a/src/arch/x86/isa/bitfields.isa b/src/arch/x86/isa/bitfields.isa
index 0404afc..dd81712 100644
--- a/src/arch/x86/isa/bitfields.isa
+++ b/src/arch/x86/isa/bitfields.isa
@@ -83,6 +83,7 @@
 def bitfield STACKSIZE stackSize;

 def bitfield MODE mode;
+def bitfield CPL mode.cpl;
 def bitfield MODE_MODE mode.mode;
 def bitfield MODE_SUBMODE mode.submode;

diff --git a/src/arch/x86/types.hh b/src/arch/x86/types.hh
index a2c2771..f377806 100644
--- a/src/arch/x86/types.hh
+++ b/src/arch/x86/types.hh
@@ -187,6 +187,12 @@
     Bitfield<2,0> submode;
 EndBitUnion(OperatingMode)

+BitUnion8(OperatingModeAndCPL)
+    Bitfield<5,4> cpl;
+    Bitfield<3> mode;
+    Bitfield<2,0> submode;
+EndBitUnion(OperatingModeAndCPL)
+
 enum X86Mode
 {
     LongMode,
@@ -236,7 +242,7 @@
     uint8_t dispSize;

     //Mode information
-    OperatingMode mode;
+    OperatingModeAndCPL mode;
 };

 inline static std::ostream &

--
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: Ie93f4f13aae002f69330606c515f369c5706c655
Gerrit-Change-Number: 55889
Gerrit-PatchSet: 1
Gerrit-Owner: Gabe Black <gabe.bl...@gmail.com>
Gerrit-MessageType: newchange
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