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arch-x86: Correct how default segments are handled.

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The stack segment is the default for instructions that use rSP or rBP in
their address calculations at all, except if they're used as a base.
Even though the wording in the AMD manual is a bit misleading, the
presence of a displacement does not make the default DS.

Also, allow segment override prefixes even if the default is SS. If an
instruction *must* use SS (like push or pop) it will have explicitly
specified that in the microcode.

Change-Id: I73c6e367440a664c5c7c483337c16d4ab14f0e34
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55589
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
This commit is contained in:
Gabe Black
2022-01-16 11:20:17 -08:00
parent cbb495334c
commit 911a8762e8
1 changed files with 6 additions and 8 deletions
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14
src/arch/x86/emulenv.cc
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@@ -100,18 +100,16 @@ void EmulEnv::doModRM(const ExtMachInst & machInst)
}
}
}
//Figure out what segment to use. This won't be entirely accurate since
//the presence of a displacement is supposed to make the instruction
//default to the data segment.
if ((base != INTREG_RBP && base != INTREG_RSP) || machInst.dispSize) {
//Figure out what segment to use.
if (base != INTREG_RBP && base != INTREG_RSP) {
seg = SEGMENT_REG_DS;
//Handle any segment override that might have been in the instruction
int segFromInst = machInst.legacy.seg;
if (segFromInst)
seg = (SegmentRegIndex)(segFromInst - 1);
} else {
seg = SEGMENT_REG_SS;
}
//Handle any segment override that might have been in the instruction
int segFromInst = machInst.legacy.seg;
if (segFromInst)
seg = (SegmentRegIndex)(segFromInst - 1);
}
void EmulEnv::setSeg(const ExtMachInst & machInst)