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

["Christoph Höger" <christoph.hoeger@celeraone.com>]

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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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