[llvm] r222767 - Small model and JIT generally don't go well with each other.

[Lang Hames]

> The default implementation does *not* do that.

That's why I suggested that we add a new mode with a memory manager that
does do that. ;)

> The necessary mmap flags are not portable either.

I don't think we'd need mmap. I'm imagining that this mode would be for
regression tests only. It would use a trivial RTDyldMemoryManager subclass
that wraps a bump-ptr allocator and reserves some small amount of memory
(~16Mb seems like it should be fine) up front.

Another item for the JIT to-do list. :)

Cheers,
Lang.

On Wed, Nov 26, 2014 at 2:25 AM, Joerg Sonnenberger <joerg at britannica.bec.de
> wrote:

> On Tue, Nov 25, 2014 at 11:07:16PM -0800, Lang Hames wrote:
> > It may be worth filing a bug for this, since we still want
> small-code-model
> > to be supported in the JIT. To make this testable we'd need to add a mode
> > to LLI that guarantees allocations compatible with small code model.
>
> As discussed with echristo on IRC, small code model for JIT does work IF
> the memory manager ensures that the constraints are implemented. The
> default implementation does *not* do that. The necessary mmap flags are
> not portable either.
>
> Joerg
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