On 09/19/2011 02:17 PM, Graydon Hoare wrote:
Can you do a bit of a what-you-know dump about the stack growth code to
a wiki page and/or mailing list post? It's a bug that blocks any sort of
public release, we need to have it working on at least *some* platforms.
Sure. Probably the best high level description is the original proposal:
http://pastebin.com/e9JMZNCE
From what is described, the LTO pass and varargs have not been
implemented yet. On the other hand, draggonegg has been patched to
support Go.
An executive summary of what is done:
*) LLVM is able to produce code that uses the API provided by newer
libgcc versions:
*) On entering a function, a check for available stack space is done
and if that fails __morestack is used to allocate more.
*) Calls to alloca are lowered in a similar way, but if the check
fails the function called is __morestack_allocate_stack_space.
The lowering is done in a way that is compatible with the pattern
matching gold does for interfacing code with and without segmented
stacks, but I don't think we currently mark the files. In any case, for
rust some other way must be implemented to not depend on gold. Adding
attributes to the functions is probably reasonable.
I *think* the libgcc functions release any allocated memory on return,
but I am not sure.
So probably the smallest effort option is to try to build a current
libgcc in the 3 platforms and use it. A quick hack to calling external
functions might be to go back to a trampoline written in assembly, but
this time it calls __morestack instead of swapping stacks as we did before.
Thanks,
-Graydon
Cheers,
Rafael
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