[BUG] CogVM crash on Windows

On 25 August 2010 04:39, Eliot Miranda <[hidden email]> wrote:
>
> Hi Levente,
>     essentially correct.  The bug was caused by an incorrect asm.  Changing
> #   define BYTE_SWAP(w) __asm__("bswap %%eax" : "=r" (w) : "r" (w))
> #   define WORD_SWAP(w) __asm__("roll $16, %%eax" : "=r" (w) : "r" (w))
> to
> #   define BYTE_SWAP(w) __asm__("bswap %0" : "=r" (w) : "r" (w))
> #   define WORD_SWAP(w) __asm__("roll $16, %0" : "=r" (w) : "r" (w))
> in platforms/win32/vm/sqWin32Window.c's byte & word image reversal code fixes it.  This worked back on 2.95.x because it always chose $eax as the register for the value variable in
> unsigned int value = *srcPixPtr++;
> but gcc 3.x is more devious.
> I've updated svn and will upload a new engine soon.
> thanks,
> Eliot
>

Hmm.. interesting, how changing a byte order could cause a crash?
A windows blitter using byte reversal logic when blitting a big-endian
forms on windows GDI (since on windows its little-endian,
it swaps form's bits, then copying bits, and then swaps back again)..
but still i don't understand how this may cause a crash.. it may cause
problems with seeing anything correct on a screen.

> On Sun, Aug 22, 2010 at 1:56 PM, Levente Uzonyi <[hidden email]> wrote:
>>
>> Hi,
>>
>>
>> evaluating [Display newDepth: x] where the value of x is 1, 4, 8 or 16 crashes the VM. No crash dump is written. If x is 2, -1, -2 or -4, then the image informs me that the depth is not available on the system. If x is -8 or -16 then the code works. For the x=16 case gdb shows the following:
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> reverse_image_words (dst=0x1450eca4, src=0x1450eca4, depth=0, width=1272,
>>    rect=0x561e60) at ../platforms/win32/vm/sqWin32Window.c:1875
>> 1875            unsigned int value = *srcPixPtr++;
>> (gdb) where
>> #0  reverse_image_words (dst=0x1450eca4, src=0x1450eca4, depth=0, width=1272,
>>    rect=0x561e60) at ../platforms/win32/vm/sqWin32Window.c:1875
>> #1  0x0043f61a in ioShowDisplay (dispBits=340847780, width=1272, height=745,
>>    depth=16, affectedL=0, affectedR=1000, affectedT=0, affectedB=0)
>>    at ../platforms/win32/vm/sqWin32Window.c:2324
>> #2  0x00403270 in displayBitsOfLeftTopRightBottom (aForm=-719257650, l=0,
>>    t=0, r=1272, b=745) at ../src/vm/gcc3x-cointerp.c:13701
>> #3  0x00405ff9 in fullDisplayUpdate () at ../src/vm/gcc3x-cointerp.c:16777
>> #4  0x0044093a in MainWndProcW (hwnd=0xf05f6, message=15, wParam=0, lParam=0)
>>    at ../platforms/win32/vm/sqWin32Window.c:447
>> #5  0x75fef8d2 in USER32!GetMessageW ()
>>   from /cygdrive/c/Windows/system32/user32.dll
>> #6  0x75fef794 in USER32!GetWindowLongW ()
>>   from /cygdrive/c/Windows/system32/user32.dll
>> #7  0x004403dc in sqLaunchDrop ()
>>    at ../platforms/win32/vm/sqWin32Window.c:2773
>> #8  0x75ff0817 in USER32!ReleaseDC ()
>>   from /cygdrive/c/Windows/system32/user32.dll
>> #9  0x75ff0a65 in USER32!GetWindowThreadProcessId ()
>>   from /cygdrive/c/Windows/system32/user32.dll
>> #10 0x776a99ce in ntdll!LdrEnumResources ()
>>   from /cygdrive/c/Windows/system32/ntdll.dll
>> #11 0x00ace008 in ?? ()
>> #12 0x00000018 in ?? ()
>> ---Type <return> to continue, or q <return> to quit---
>> #13 0x00ace058 in ?? ()
>> #14 0x776a9980 in ntdll!LdrDisableThreadCalloutsForDll ()
>>   from /cygdrive/c/Windows/system32/ntdll.dll
>> #15 0x0204c1d8 in ?? ()
>> #16 0x0000000f in ?? ()
>> #17 0x00000000 in ?? ()
>> (gdb) info registers
>> eax            0xd520ffce       -719257650
>> ecx            0x3      3
>> edx            0x0      0
>> ebx            0x1f4    500
>> esp            0xacd5b4 0xacd5b4
>> ebp            0x0      0x0
>> esi            0x1511a000       353476608
>> edi            0x1511a000       353476608
>> eip            0x43ed0c 0x43ed0c <reverse_image_words+353>
>> eflags         0x10216  [ PF AF IF RF ]
>> cs             0x1b     27
>> ss             0x23     35
>> ds             0x23     35
>> es             0x23     35
>> fs             0x3b     59
>> gs             0x0      0
>>
>> It may be a compiler bug, because the 4.0.2 SqueakVM doesn't have this issue. It's a bit suspicious that depth is 0 here:
>> #0  reverse_image_words (dst=0x1450eca4, src=0x1450eca4, depth=0, width=1272,
>>    rect=0x561e60) at ../platforms/win32/vm/sqWin32Window.c:1875
>> but the value of depth is known at compilation time (16), so it may be some compiler "magic".
>> Here are the values of the variables in the method:
>> (gdb) p dst
>> $2 = (unsigned int *) 0x1450eca4
>> (gdb) p src
>> $3 = (unsigned int *) 0x1450eca4
>> (gdb) p depth
>> $4 = 0
>> (gdb) p width
>> $5 = 1272
>> (gdb) p rect
>> $6 = (RECT *) 0x561e60
>> (gdb) p rect->left
>> $7 = 0
>> (gdb) p rect->right
>> $8 = 1000
>> (gdb) p rect->top
>> $9 = 0
>> (gdb) p rect->bottom
>> $10 = 745
>> (gdb) p pitch
>> $11 = 353476608
>> (gdb) p first
>> $12 = 3
>> (gdb) p last
>> No symbol "last" in current context.
>> (gdb) p nWords
>> $13 = 500
>> (gdb) p delta
>> $14 = 0
>> (gdb) p yy
>> $15 = 0
>> (gdb) p srcPixPtr
>> $16 = (DWORD *) 0x1511a000
>> (gdb) p dstPixPtr
>> $17 = (DWORD *) 0x1511a000
>> (gdb) p i
>> $18 = -719257650
>> (gdb) p value
>> $19 = 0
>>
>>
>> Cheers,
>> Levente
>
>
>

--
Best regards,
Igor Stasenko AKA sig.