[ppc] Default stack size on ppc64

[David Woodhouse]

On Tue, 2015-03-24 at 11:35 -0500, Steven Munroe wrote:
> I am not sure how ocaml is generating code for PPC64, you could look in
> to split stack support, but at this time GCC does not implement split
> stack.
         ... for PPC64.

I wouldn't want to do it in OCaml before it's supported in GCC and the 
runtime. But once it *is*, it shouldn't be hard to make OCaml support 
it.

It's mostly just a matter of emitting the right instructions in the 
function prologue and epilogue, in emit.mlp.

But it does depend on the runtime support for allocating more stack 
while not overflowing the 'slop' space on the existing stack, and 
linker support for expanding the stack frame size when calling through 
to legacy non-split-stack functions, and probably other things. So not 
something we'd want to do purely within OCaml.

I'm a little confused about what the problem is, though.

If the compiler is single-threaded, and increasing the stack ulimit 
fixes the problem, that implies that the default stack ulimit is less 
than the 8MiB-64KiB that it takes to reach the guard page... can that 
be right? Richard, what does 'ulimit -s' report *before* you increase 
it?

-- 
dwmw2
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