Re: Help tracking down libpth problem on ia64?

[Richard Harke <rharke@earthlink.net>]

I have found the problem and will be sending you a diff
file in a separate email. The problem is due to the unique structure
of the stack on ia64. libpth would write a unique value into
the end of the stack and then check to see if it changed as a
test for stack overrun. But linux ia64 uses that part of the stack
memory for the register backing store so the test location is
sure to be over written. I have put in a different test that checks
for a meet in the middle.

This experience brings some questions to my mind. On some systems
the stack is given a very high virtual address but only a (relatively)
small amount of real memory is mapped in. Then if the user goes off
the end of the stack, there is a page fault and the system has the
possiblity to extend the stack. On the ia64, this hardly seems
feasible. Even if one contemplated extending the stack by copying
the backing store down, there doesn't seem to be any way to detect
when more memory is required until it is too late.

Of course, in libpth the check is only made when a thread switch
is made and if an overrun is detected, the fix is to rebuild the
program with a larger stack size.

Richard Harke


On Thursday 08 January 2004 06:20 pm, Jamin W. Collins wrote:
> On Thu, Jan 08, 2004 at 03:01:24PM -0800, Richard Harke wrote:
> > I haven't seen anyone else respond to this so I'll
> > jump in. If you can point me to the source package, I'll
> > take a look at it.
>
> "apt-get source pth" should give you the source for pth.  "apt-get
> build-dep pth" should make sure you have the necessary packages
> installed to build it.
>