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Fixed a stack-size bug uncovered by a PUSH SS/POP SS sequence in Windows 95 kernel

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This commit is contained in:
Jeff Parsons 2015-09-11 15:13:08 -07:00
commit cb9e330cfa
4 changed files with 63 additions and 2 deletions
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15
modules/pcjs/lib/x86cpu.js
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@ -2173,7 +2173,20 @@ X86CPU.prototype.setSS = function(sel, fInterruptable)
var regESP = this.getSP();
var regLSP = this.segSS.load(sel);
if (regLSP !== X86.ADDR_INVALID) {
this.regLSP = (regLSP + regESP)|0;
/*
* The safest way to update regLSP after a potential change to segSS.base is to call setSP()
* with the original stack pointer retrieved above via getSP(). When I tried to be clever and
* do this instead:
*
* this.regLSP = (regLSP + regESP)|0;
*
* 16-bit stacks began inadvertently using ESP instead of SP. The moral: don't be needlessly clever.
*
* Sprinkle the following assert throughout stack operations to catch that bug in the future:
*
* this.assert(!((this.regLSP - this.segSS.base) & ~this.segSS.maskAddr));
*/
this.setSP(regESP);
if (this.segSS.fExpDown) {
this.regLSPLimit = (this.segSS.base + this.segSS.maskAddr)|0;
this.regLSPLimitLow = (this.segSS.base + this.segSS.limit)|0;