[Bug 10503] Sid Meier's Alpha Centauri: Wine segfaults when clicking on a city.

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=10503





--- Comment #9 from Anastasius Focht <focht at gmx.net>  2007-11-19 17:31:59 ---
Hello again,

well I thought about this problem further.
Although an alternate stack for the raise frame would let the vectored
X11DRV_DIB_FaultHandler execute successfully to handle the DIB reads/writes,
wine wouldn't be able to recover later.
When returning from raise handler, wine needs to restore faulting threads full
register set from saved context.

The typical sequence goes as follows (excerpt from 
__wine_call_from_32_restore_regs):

--- snip ---
..
push    dword ptr [ecx+0C8h]   ; CONTEXTOFFSET(SegSs)
pop     ss
mov     esp, [ecx+0C4h]        ; CONTEXTOFFSET(Esp)
push    dword ptr [ecx+0C0h]   ; CONTEXTOFFSET(EFlags)  *boom*
push    dword ptr [ecx+0BCh]   ; CONTEXTOFFSET(SegCs)
push    dword ptr [ecx+0B8h]   ; CONTEXTOFFSET(Eip)
push    dword ptr [ecx+98h]    ; CONTEXTOFFSET(SegDs)
mov     ecx, [ecx+0ACh]        ; CONTEXTOFFSET(Ecx)
pop     ds
iret
--- snip ---

Well, as soon as the abused ESP is reloaded from faulting thread context any
further restore will fail (likely causing another access violation).
I'm not aware of a wine-compatible method (user mode only code) to emulate iret
*and* swap stacks.

Interestingly this piece of game code was produced by Microsoft Visual C++ 5.0
compiler ...
Who else could produce such brain damaged code ... ok, I've seen several gcc
brain damage as well ;-)

There are 24 occurrences of this abusive (DIB) code.
Whatever optimization was done ... the compiler simply ran out 8 GP registers
and resorted to use ESP/EBP in favor of stack vars - leaving wine's DIB
handling mechanism in distress.

I would vote for WONTFIX (until someone decides to change the way DIBs are
handled) ;-)

Regards


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