x86 address calculation for expand-down segments?

Posted on 2019-04-20, 13:35

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by superfury

in PC Emulation

in PC Emulation

Is the expand-down segment's linear address calculated differently from expand-up segments? I have, for example, a descriptor which points to a base address of 0x80000000. Then that is a kernel stack(of course differently for different operating systems, but it's just for simplicity). If I have a 16 …

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Re: UniPCemu Windows 95/NT progress and issues

Posted on 2019-04-20, 11:17

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by superfury

in PC Emulation

in PC Emulation

Just gave OS/2 a try again. It immediately crashes trying to load CR2 with a value. Then I found out that it was checking bit 31 and 0 for invalid values for CR0, while actually loading the a non-CR0 control register:S Immediately fixed that. Now it at least continues on to the initial screen of the …

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Re: Are expand-down segments without valid offsets used?

Posted on 2019-04-12, 15:11

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by superfury

in PC Emulation

in PC Emulation

@retardware: I mean a 16-bit segment top-down segment descriptor loaded with a limit of FFFF to FFFFFh. That descriptor will load into the descriptor cache without any problem(e.g. MOV DS,AX), but when software tries to access ANY address(doesn't matter which one), it results in a #GP(0) fault …

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Are expand-down segments without valid offsets used?

Posted on 2019-04-12, 08:28

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by superfury

in PC Emulation

in PC Emulation

I know that a maximum-size(FFFFh to FFFFFh in the limit fields) for a expand-down segment has no valid offsets, but can still be loaded into a segment selector if present. Is that behaviour used with any operating systems or extenders to trap accesses to certain segment data selectors(but allowing …

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Re: How does Dosbox manage to get so much performance in it's interpreting CPU emulation?

Posted on 2019-04-09, 20:52

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by superfury

in DOSBox Development

in DOSBox Development

So simply said, does anyone have some good optimization advice regarding x86 CPU emulation optimization? No matter what, the current bottleneck still seems to be the innermost CPU handling, in particular the applymemoryholes function combined with the invalid memory 'if'-statement at it's calling …

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Re: How does Dosbox manage to get so much performance in it's interpreting CPU emulation?

Posted on 2019-04-08, 19:17

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by superfury

in DOSBox Development

in DOSBox Development

Well, UniPCemu isn't Dosbox(it doesn't try to cut corners for performance by breaking compatibility). Still, it's kind of strange that Dosbox takes ~0% CPU for 3MIPS at 100% speed, while UniPCemu barely keeps up(25%-30% speed of 3MIPS taking ~17% of an Intel i7-4790K@4.0GHz). Most of the time issue …

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Re: How does Dosbox manage to get so much performance in it's interpreting CPU emulation?

Posted on 2019-04-08, 18:47

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by superfury

in DOSBox Development

in DOSBox Development

Won't such a basic protection mechanism missing in Dosbox break software(writing to r/o segments)? Also, UniPCemu 'cheats' just a little bit, when prefetching the PIQ to become as full as possible, by checking the first byte to fetch, then the last one(to allow page faults to happen), working back …

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Re: How does Dosbox manage to get so much performance in it's interpreting CPU emulation?

Posted on 2019-04-08, 11:28

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by superfury

in DOSBox Development

in DOSBox Development

Not currently. The main issue being that the debugger also reads said flags after each instruction. They don't show up in the profiling(it basically uses the same methods as Bochs does for a large part for calculating those, except not lazily). UniPCemu arithmetic flags(not all of them, but the …

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How does Dosbox manage to get so much performance in it's interpreting CPU emulation?

Posted on 2019-04-08, 07:49

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by superfury

in DOSBox Development

in DOSBox Development

How did Dosbox manage to get so much performance out of it's CPU that's in interpreter(non-dynamic recompilation) mode? I can't get UniPCemu past 25%(top 30% if lucky) at 3 MIPS speed. Anyone got tips on how to improve performance? I know it uses a big lookup table for it's handling of Paging …

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x86 opcodes 0FB7 and 0FBF 16-bit?

Posted on 2019-04-08, 07:08

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by superfury

in PC Emulation

in PC Emulation

Do opcodes 0FB7 and 0FBF(MOVS/ZX) in 16-bit mode function like a normal MOV(without sign extension to 32-bit, since it's from a 16-bit memory/register location to 16-bit register)? Or do they always extend to a 32-bit register, regardless of operand size? I already implemented it in both 16-bit( …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-04-07, 18:39

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by superfury

in PC Emulation

in PC Emulation

I did see something interesting while Windows 95(a) setup was starting up it's GUI(at least until displaying the welcome to setup screen): it keeps trying to throwing #NP faults for a RETF to segment E0h? Anyone knows anything about that? It doesn't seem to stop throwing them at some point, they …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-04-06, 18:16

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by superfury

in PC Emulation

in PC Emulation

Just improved the handling of the setting of the Accessed bit of the segment descriptor(only when a descriptor reaches a segment's descriptor cache). Interestingly enough, Windows 95 now seems to completely hang due to infinite ARPL faults being thrown(or what looks like them anyways)? It's opcode …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-04-02, 22:15

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by superfury

in PC Emulation

in PC Emulation

I've made a little log of the real mode part of Windows 3.0 booting(from command prompt, pressing enter(and having "win" already typed): https://www.dropbox.com/s/ynaebhcez40om5c/debugger_windows30_booting_386enhancedmode_realmodepart_UniPCemu_20190401_0120.7z?dl=0 Anyone can see why ESI is …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-04-01, 08:24

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by superfury

in PC Emulation

in PC Emulation

Looking upwards, I see the address being written to memory at 0028:80006c3b. Further up, it's source is LA 8001523c. Hmmm.... [8001523c] is only used by inc and mov in UniPCemu, while only used by cmp and mov in win30_3.txt? Since said location reads as a 32-bit integer, does that mean there's an …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-03-31, 19:36

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by superfury

in PC Emulation

in PC Emulation

This is a log of UniPCemu booting Windows 3.0 in enhanced mode, with MS-DOS 6.22 and it's HIMEM.SYS, Windows' EMM386.SYS(~300KB EMS memory?) and failing drive preload program(can't remember it's name) from the Windows directory(which says invalid MS-DOS version?). I've executed win without …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-03-30, 17:38

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by superfury

in PC Emulation

in PC Emulation

Just reinstalled Windows 3.0a and fixed the config.sys drivers to use it properly. Now, running Windows 3.0 in 386 enhanced mode(with himem.sys and emm386.sys loaded(emm386 reporting 256k memory)), EMM386 crashes with a "EMM386 Exception error #08 - press ENTER to reboot". So a double fault occurs …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-03-30, 16:52

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by superfury

in PC Emulation

in PC Emulation

Just retried Windows 3.0a with HIMEM and EMM386 from the Windows folder loaded, running it with the /3 switch for 386 Enhanced mode. It seems to hang/crash on a HLT at 0000:0000, previous opcode being at 0048:0868?

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-03-30, 11:26

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by superfury

in PC Emulation

in PC Emulation

Hmmmm... Since Windows 3.x in real and standard mode exhibit the same issue with the PS/2 keyboard, and the PS/2 keyboard is working properly(generating XT scancodes properly) and the MS-DOS prompt doesn't see it in that case, that would mean there's a real mode cpu problem? And since it's built for …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-03-30, 09:37

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by superfury

in PC Emulation

in PC Emulation

Managed to fix two PS/2 keyboard bugs(command F3(set key delay/rate) not being handled properly since emulating at cycle accuracy and the 8042 output buffer being filled with the escape F0 part of the scancode without setting status bit 0, being changed to fully handled properly again and leaving …

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Re: Any good MS-DOS 80386/80486 games for testing Virtual memory support?

Posted on 2019-03-29, 15:44

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by superfury

in PC Emulation

in PC Emulation

Any games that you know of requiring all 80286 protected mode functionality to work and run properly? So proper interrupts, task switching, gates, segmentation etc.? So essentially everything that's not 32-bit and paging? Edit: A bit of progress on Windows 3.0. It's finally running in Standard mode! …

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