Date: Mon, 21 Jun 1999 09:07:44 +0300 (IDT)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender: eliz AT is
To: Erik Berglund <erik2 DOT berglund AT telia DOT com>
cc: Andris Pavenis <pavenis AT lanet DOT lv>, djgpp-workers AT delorie DOT com
Subject: Re: Re: gcc-crash - and a possible solution
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On Sun, 20 Jun 1999, Erik Berglund wrote:

> > > Call frame traceback EIPs:
> > >   0x00175777 _free+119
> > >   0x00173755 _obstack_free+49
> > >   0x000dbcb6 _reload+3730
> > 
> > This looks like some code is overwriting a buffer allocated by
> > malloc, or freeing some buffer that is already freed.

On second thought, there's something else strange here: the address of
`free' is abnormally high.  Usually, it lives somewhere in the 0x1NNN
region, because the startup code calls it.

Andris, does GCC use an alternate version of malloc/free, like GNU's
malloc?  If so, then using Unixy `sbrk' *is* the solution, since
gmalloc expects the Unixy behavior and will break otherwise.

If GNU's malloc is not used, then how come `free' has such a high
address?

> Hmmm. Could it be an uninitialized stack variable somewhere in
> gcc?

Stack space isn't malloc'ed, it is allocated by a direct call to
`sbrk' in crt0.S.

> Because the error seems to depend on a certain program
> sequence previously run, that is, the state of the RAM bits
> (128 Mbyte, that is 1 Gbit).

Don't forget that the heap (the space used for malloc'ed storage) also
inherits whatever garbage was in RAM before, since DJGPP's `malloc'
doesn't zero out the allocated buffer (to prevent large run-time
penalties due to accessing the allocated memory).