pc386 BSP memory management [was: Re: assert in malloc.c:383]

[Joel Sherrill <joel@OARcorp.com>]

Karel Gardas wrote:
> 
> Thanks Sergey and Joel with this issue. Unfortunatelly it does not seem to
> be so easy.
> 
> On Fri, 14 Jan 2005, Joel Sherrill <joel at OARcorp.com> wrote:
> 
> 
>>>my question is: how to prevent it? Is assert on this place really needed,
>>>especially when I consider that you set errno on this place. What does
>>>this assert mean?
>>
>>This means you are freeing memory which was not allocated from
>>the heap.  The address given to free MUST match that given to
>>you by malloc.  So this could be a double free or a free of a bogus
>>address.
> 
> 
> OK, I've commented out one delete and everything started working well,
> then I've un-commented this code again, recompile and everything is still
> working well. Not only this is an issue, I've also hited it (this assert
> in free) on different place in this code -- but just once from about 50
> test starts of server/client so it looks quite strange, which leads me to
> the question about RTEMS memory management on pc386 BSP. I'm most
> interested in memory size limits/code size limits for this BSP, since in
> powerpc/arm support I've seen some hard limits for RAM size in linkcmds
> scripts which leads me to the care if the same also apply to i386/pc386
> BSP platform, but I'm not able to "decode" pc386 linkcmds to find out if
> it contains some limits or not. The reason for this ask is that compiled
> MICO binary is quite big and also it might consume some memory and I
> wouldn't like to hit some memory override issue with this. May I even
> assume that RTEMS pick-up the RAM size from BIOS? i.e. if I play with
> different Qemu setup for different memory sizes, will RTEMS use different
> memory sizes too? I'm still talking only about pc386 BSP here.

If this is with a MICO test, you could be overflowing a task stack.

The RAM available is a function of the board.  On the PC386 BSP, it
is supposed to probe and dynamically size the RAM.  But this is only
used to size the C program heap.  Each task has a fixed size stack
determined at its create time.

RTEMS has some stack checking code which checks at each task switch
if you have overrun your stack at any time.


> Thanks a lot,
> Karel
> --
> Karel Gardas                  kgardas at objectsecurity.com
> ObjectSecurity Ltd.           http://www.objectsecurity.com
> 


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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