Messages in this thread | | | Date | Thu, 01 Aug 2002 15:43:34 +0200 | From | Kasper Dupont <> | Subject | Re: [patch] vm86: Clear AC on INT |
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Stas Sergeev wrote: > > Hello. > > According to this: > http://support.intel.com/design/intarch/techinfo/Pentium/instrefi.htm#89126 > AC flag is cleared by an INT > instruction executed in real mode. > The attached patch implements that > functionality and solves some > problems recently discussed in > dosemu mailing list.
This sounds a little strange to me. AC is in the upper 16 bit of the EFLAGS register, so it is not saved on an interrupt where only lower 16 bits is saved. This means that when we clear it on the interrupt, the value will be lost for good.
I can see the spec says it, so we'd better do that. But does the spec make any sense? And does the CPU really loose the AC flag on every interrupt in real mode?
A few other things got me wondering, it says there is tested for enough space in the stack. Does this mean something like if (SP<6) trap(); ? If it does, we should change do_int to actually do this. And how should we actually trap if there is not enough space for pushing values?
And does this testing apply to other instructions as well?
And it also says the IDT size is tested. But does that concept even exist in real mode?
And finally, why do we have a 32 bit IRET instruction, but no 32 bit INT instruction? Is that really correct?
-- Kasper Dupont -- der bruger for meget tid på usenet. For sending spam use mailto:razrep@daimi.au.dk or mailto:mcxumhvenwblvtl@skrammel.yaboo.dk - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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