I am not at all an expert on this, so maybe some one else
on the list might enlighten us, but given what you wrote I
did some experiments. I added a local variable in the function
suspproc() allocating some extra space on the stack.

Without setting a bigger font, it seems to be possible to allocate
another 17 bytes on the stack without crashing. Upon allocating
an array of 18 bytes, it crashes for me.

So it looks like the programmer allocated exactly the amount
of headroom needed (at that time) and nothing more. It is
quite plausible that something that is bigger in a 64bit world
(larger datatypes or alignment padding) could consume those
few extra bytes.

It would be interesting to hear if there has been similar problems
with other programs, e.g. while converting to amd64, and how
you usually determine how much of stack to allocate, by trial and
error, or by calculating?

Jonas

2017-07-09 08:51 skrev Alex Musolino:

What caused you to find the bug? Maybe some other means than with changing the font.

I also use a non-default font but have only recently started using
amd64 kernels.  If I changed back to /lib/fonts/bit/vga/unicode.font I
don't see the problem anymore.  Originally I thought that the larger
size of pointers on amd64 was causing the stack to be exhausted, but
now I'm not sure what's going on.  There seems to be nothing obviously
font-related in the suspproc thread.

--
Cheers,
Alex Musolino