Re: [Caml-list] How is the frametable handled when throwing exceptions?

["Nicolás Ojeda Bär" <nicolas.ojeda.bar@lexifi.com>]

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Hi Christoph,

Someone who knows more will be able to get a better answer, but I don't
think there is much of an issue here:
when using the C API to register local roots (CAMLparam, CAMLlocal, etc),
these roots are in effect
stored in the C stack.  When raising an exception the stack is _cut down_
and all those roots
are promptly forgotten (as they should be).

Cheers,
Nicolas


On Sat, Feb 11, 2017 at 3:02 PM, Christoph Höger <
christoph.hoeger@celeraone.com> wrote:

> Dear all,
>
> while studying camls native code generation and garbage collection
> strategy, I came upon Connor Benner's bachelor thesis from 2012, where he
> implemented a llvm backend for ocamlopt. One intriguing remark mentioned
> OCamls exception mechanism as basically consisting a pointer to the stack
> frame of the last exception handler in a special register (r14, when I
> recall correctly). Throwing an exception that becomes a mov/pop/ret
> operation. This however, seems to interfere with garbage collection: From
> the C-API, it seems that all local roots are stored in the frametable via
> some special macros (e.g. CAMLParam, CAMLlocal).
>
> When control just returns from a stack frame, how are the entries removed
> from the frametable?
>
> I would be glad, if someone could answer this or point me to the relevant
> documentation (if any exists).
>
> thanks,
>
> Christoph
>

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