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Fixed high 8-bit register MOVs, restricted ACCESSED bit updates to SEGMENT descriptors, and prevented the Debugger from looping endlessly on bad instructions

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This commit is contained in:
Jeff Parsons 2015-08-20 22:42:27 -07:00
commit 2d7cbe2864
4 changed files with 33 additions and 28 deletions
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38
modules/pcjs/lib/x86seg.js
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@ -1194,6 +1194,26 @@ X86Seg.prototype.updateMode = function(fLoad, fProt, fV86)
if (this.checkWrite == this.checkWriteProt) this.checkWrite = this.checkWriteProtDown;
this.fExpDown = true;
}
if (fLoad && this.id < X86Seg.ID.VER) {
/*
* We must update the descriptor's ACCESSED bit whenever the segment is "accessed" (ie,
* loaded); unlike the ACCESSED and DIRTY bits in PTEs, a descriptor ACCESSED bit is only
* updated on loads, not on every memory access.
*
* We compute address of the descriptor byte containing the ACCESSED bit (offset 0x5);
* note that it's perfectly normal for addrDesc to occasionally be invalid (eg, when the CPU
* is creating protected-mode-only segment registers like LDT and TSS, or when the CPU has
* transitioned from real-mode to protected-mode and new selector(s) have not been loaded yet).
*
* TODO: Note I do NOT update the ACCESSED bit for null GDT selectors, because I assume the
* hardware does not update it either. In fact, I've seen code that uses the null GDT descriptor
* for other purposes, on the assumption that that descriptor is completely unused.
*/
if ((this.sel & ~X86.SEL.RPL) && this.addrDesc !== X86.ADDR_INVALID) {
var addrType = this.addrDesc + X86.DESC.ACC.TYPE.OFFSET;
this.cpu.setByte(addrType, this.cpu.getByte(addrType) | (X86.DESC.ACC.TYPE.ACCESSED >> 8));
}
}
}
/*
* TODO: For non-SEG descriptors, are there other checks or functions we should establish?
@ -1204,24 +1224,6 @@ X86Seg.prototype.updateMode = function(fLoad, fProt, fV86)
* we're updating segment registers as part of a mode change.
*/
if (fLoad) {
/*
* We must update the descriptor's ACCESSED bit whenever the segment is "accessed" (ie,
* loaded); unlike the ACCESSED and DIRTY bits in PTEs, a descriptor ACCESSED bit is only
* updated on loads, not on every memory access.
*
* We compute address of the descriptor byte containing the ACCESSED bit (offset 0x5);
* note that it's perfectly normal for addrDesc to occasionally be invalid (eg, when the CPU
* is creating protected-mode-only segment registers like LDT and TSS, or when the CPU has
* transitioned from real-mode to protected-mode and new selector(s) have not been loaded yet).
*
* TODO: Note I do NOT update the ACCESSED bit for null GDT selectors, because I assume the
* hardware does not update it either. In fact, I've seen code that uses the null GDT descriptor
* for other purposes, on the assumption that that descriptor is completely unused.
*/
if ((this.sel & ~X86.SEL.RPL) && this.addrDesc !== X86.ADDR_INVALID) {
var addrType = this.addrDesc + X86.DESC.ACC.TYPE.OFFSET;
this.cpu.setByte(addrType, this.cpu.getByte(addrType) | (X86.DESC.ACC.TYPE.ACCESSED >> 8));
}
this.cpl = this.sel & X86.SEL.RPL;
this.dpl = (this.acc & X86.DESC.ACC.DPL.MASK) >> X86.DESC.ACC.DPL.SHIFT;
if (this.cpu.model < X86.MODEL_80386 || !(this.ext & X86.DESC.EXT.BIG)) {