On Friday, 17 August 2012 at 12:36:57 UTC, R Grocott wrote:
Paulo -
Surely there are ways to work around the OS's native ABI,
though, even from within compiled code?
Rewriting object vtables (etc.) might be a bit more involved
than simple name mangling, but I'm almost certain it would be
possible to implement it as part of druntime. The blog post
which I linked describes one way to go about it.
Michael -
As far as I can tell, most of the performance cost in your idea
comes from the additional level of indirection, since you store
vtable offsets in a global variable which must be read before
each function call.
This might just be wishful thinking, but would it be possible
for druntime to write new vtable offsets directly into the
program's machine code, at dynamic-link time? That would remove
all of the run-time performance overhead, but, as I say, I'm
not sure whether it's actually possible.
I think the biggest obstacle is that it would require the .text
section (or equivalent) of the executable to be writable. I
know that's possible on Linux, but I'm not sure whether the
same is true for most other operating systems. I guess it might
also be a security risk?
It's possible to modify the vtable at runtime. Just access
through .__vtable in ClassInfo (I think) and treat it like a
regular array. Don't know if that's what you mean.
--
/Jacob Carlborg
