request for stack advice

[Joe Buck]

On Mon, Apr 26, 2004 at 11:41:10AM -0500, Justin M. Lee wrote:
> I recently inherited some C that crashes when compiled with 3.2-3.3
> compilers on Linux x86.  It works on SGI's compiler on Irix and gcc 2.95
> on Linux x86.
> 
> This code is a bit strange - it puts huge arrays on the stack.  We're
> talking about several megs.  In a debugger, it appears that the crash
> happens when it tries to touch something on the stack in a particular
> call.  I came to realize that I don't understand how stack allocation
> works.  Looking at the assembly code, a function doesn't really request
> more stack -- it just subtracts from esp.  How does the OS know to
> allocate pages to the stack area?  I saw something about stack space in
> the ld man page, but it didn't know what I was talking about when I tried
> to pass it in via -Xlinker.  Is there a default stack space?

This is operating system-dependent.  Within a certain size range, the
stack will be automatically grown by the OS, but if this size limit is
exceeded, you'll get faults.

> Some more info: it looks to me like the esp is valid at the point of the
> crash: its about 8 megs less at the point of the crash than at main.  The
> reason I even got here was because I thought the stack was getting
> trashed.

8 megs sounds like the typical default stack size.  It can be changed with
"ulimit" (or "limit" if you use csh or tcsh).