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Naked pointers and the bytecode interpreter #9680

Merged
merged 5 commits into from Jun 21, 2020
Merged

Naked pointers and the bytecode interpreter #9680

merged 5 commits into from Jun 21, 2020

Commits on Jun 18, 2020

  1. callback.c: register the bytecode fragment used for callbacks 

    So that the return address pushed on the bytecode interpreter stack
is correctly recognized as a code pointer.
    @xavierleroy
    xavierleroy committed Jun 18, 2020
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  2. Revised linking of trap frames in bytecode interpreter stack 

    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.
    @xavierleroy
    xavierleroy committed Jun 18, 2020
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  3. Revised scanning of bytecode interpreter stack 

    In no-naked-pointers mode, recognize and skip code pointers present in
the stack of the bytecode interpreter.  This is needed only for
the scan at beginning of a major GC cycle, not for the scan done
at every minor GC.
    @xavierleroy
    xavierleroy committed Jun 18, 2020
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  4. major_gc.c: use no-naked-pointers mode even in bytecode 

    Earlier, no-naked-pointers mode was effective only in native code.
    @xavierleroy
    xavierleroy committed Jun 18, 2020
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  5. interp.c: remove two assertions that cannot be checked without the pa… 

    …ge table

`!Is_in_value_area(pc)` is always false if we turn the page table off.
A better check would be `caml_find_code_fragment_by_pc(pc) != NULL`,
but I feel this is too costly even for the debug mode of the interpreter.
    @xavierleroy
    xavierleroy committed Jun 18, 2020
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