Re: [Tuxmath-devel] Fix for new Windows TuxMath bug

[David B. <dav...@gm...>]

Hi - thanks for this important fix.

David Bruce

On Tue, Apr 10, 2012 at 12:43 AM, Kento Locatelli <me...@kl...>wrote:

> Hey all,
>
> I was bored so I cross-compiled TuxMath for Windows, but the game kept
> quitting when I tried to start a mission. Seg Fault!
> http://pastie.org/3759844
>
> After mucking around in gdb, I found and fixed the problem... I attached
> the diff git gave me since I don't have write access to the git repo (diff
> for the head of the tuxmath t4k-0.1.1 branch). I haven't used C since
> high-school, so it might not be the ideal way...
>
> Basically the problem is the MC_MathGame instance's question pointers are
> never explicitly initialized to null. The contents of the memory block
> malloc returns are implementation dependent, and on Windows apparently that
> can mean a block of memory filled with 0xbaadf00d [1]. Since MC_Initialize
> doesn't initialize the question pointers, we're left with a bunch of
> not-null pointers to invalid memory... obviously a problem. So, the simple
> fix is to explicitly initialize them to null.
>
> Note: this isn't currently a problem on linux - which zeroes memory that
> wasn't previously allocated to the program (for security) - nor is there a
> problem with the Windows executable on the site - which was built back when
> MC_MathQuestion were globals that were explicitly initialized to null.
>
> Cheers!
> Kento Locatelli
>
> [1] https://en.wikipedia.org/wiki/**Magic_number_(programming)#**
> Magic_debug_values<https://en.wikipedia.org/wiki/Magic_number_(programming)#Magic_debug_values><
> https://en.wikipedia.org/**wiki/Magic_number_%**
> 28programming%29#Magic_debug_**values<https://en.wikipedia.org/wiki/Magic_number_%28programming%29#Magic_debug_values>>
>
>
>
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-- 
David Bruce

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