Load the debug information during runtime startup if OCAMLRUNPARAM=b=2.
This guards against the specific case of running out of fds, since the
debug information can't then be loaded.
Rather than storing a pointer to the previous frame in the Trap_link
field of the current frame, store the distance (pointer difference)
between the current frame and the previous frame, tagged as an OCaml
integer.
Using a tagged integer instead of a raw pointer means fever problems
later with strict no-naked-pointer support.
Using a distance rather than an absolute address simplifies
the code that resizes the stack.
The previous mechanism worked for C calls that raise an exception, but not for C calls that call back into OCaml code which raises an exception.
This commit addresses the issue by saving the PC in the interpreter stack before a C call, so that the backtrace mechanism always sees it.
However, if an external is declared in the .ml file and exposed in the .mli file as a val, then ocamlc generates a wrapper that adds a spurious entry in the stack frame. In this PR, this change in behavior results in the re-declaration of Printexc.get_callstack as an external instead of a val, so that the spurious stack frame does not appear in call stacks obtained from Printexc.get_callstack.
Since we cannot access backtrace position in cmmgen.ml anymore,
Cmm.raise_kind in removed. Instead, we use Lambda.raise_kind. When
assembly code is generated, we reset the backtrace position to 0 in the
case of regular raise. Importantly, the semantics remains the same.
This commit adds dynlink support for ocamldebug. As a side effect, it also:
- factorizes the various functions searching for a code fragment into one,
called [caml_find_code_fragment];
- removes the [caml_register_code_fragment], which does not seem to
be used anywhere, and which clearly should not be used by external code.
David Allsopp
Stephen Dolan
Xavier Leroy
Jérémie Dimino
Nicolás Ojeda Bär
Gabriel Scherer
Jacques-Henri Jourdan
KC Sivaramakrishnan
Stephen Dolan
Sébastien Hinderer