Hermès Bélusca-Maïto
5887b17005
CORE-11921 CORE-13715 (Regression introduced by commit2e1b82cf, r44841.) In some cases the number of valid (!= 0xFFFF) entries in the IOPM can be larger than the assumed size (32) of the entries cache. The maximum possible number of entries is equal to IOPM_SIZE / sizeof(USHORT). A way to reproduce the problem is as follows: start ReactOS in debugging mode using '/DEBUG /DEBUGPORT=SCREEN' . Then manage to break into the debugger exactly during the execution of Ke386CallBios() triggered by display initialization (for example in my case, while a video driver was being initialized via the HwInitialize() call done by videoport inside IntVideoPortDispatchOpen() ). When this happens, a "concurrent" execution between Ke386CallBios() and the HAL function HalpStoreAndClearIopm() takes place. This is due to the fact that when entering the debugger in SCREEN mode, the following call-chain holds: InbvResetDisplay() -> VidResetDisplay() -> HalResetDisplay() -> HalpBiosDisplayReset() -> HalpSetupRealModeIoPermissionsAndTask() -> HalpStoreAndClearIopm(). However, the code of Ke386CallBios() has reset the IOPM contents with all zeroes instead of 0xFFFF, and this triggers the caching of all the entries of the IOPM by HalpStoreAndClearIopm(), whose number is greater than the wrongly assumed number of '32'. As Thomas explained to me, "Windows supports [the maximum number of IOPM entries], it just makes a full copy of the table instead of this indexed partial copy." And I agree that this overengineered so-called "optimization" committed in2e1b82cfcontributed in introducing an unnecessary bug and making the code less clear. Also it makes the IOPM cache larger than the necessary size by twice as much. Finally, Ke386CallBios() also caches IOPM entries before doing a 16-bit call, and obviously uses the more straightforward way of doing a direct copy of the IOPM table (using RtlCopyMemory()). I wonder what kind of "optimization" this tried to achieve, knowing that we are not doing like thousands of 32->16bit BIOS interrupt calls per second in ReactOS...
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ReactOS™ is an Open Source effort to develop a quality operating system that is compatible with applications and drivers written for the Microsoft® Windows™ NT family of operating systems (NT4, 2000, XP, 2003, Vista, Seven).
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