Re: query: debugging dynamically generated code

debray@CS.Arizona.EDU (Saumya K. Debray) wrote
> How to people go about debugging code that's being
> generated/transformed dynamically? (My one experience, using gdb, was
> painful at best -- e.g., if I didn't get my timing right, and the
> dynamically generated code overwrote a breakpoint, gdb would
> nevertheless insist that I had a breakpoint at that address and refuse
> to let me set another one at that location.)
>
> Given the amount of interest and activity in JIT compilers and dynamic
> code optimization in recent years, I expect there's a fair amount of
> experience with, and literature on, this topic (though citeseer didn't
> turn up anything obvious). I'd be grateful for any pointers.


    Look for "debugging self-modifying code". There are a lot of
references about it, mostly claiming negative experience. In viruses
and program protection, the only purpose of self-modifying code is to
make it less comprehensible and debuggable.
    A debugger that is capable to debug self-modifying code might run
much slower. For example, one of the solutions would be to make the
"code" pages read-only and the "data" pages not executable, to catch
all the writes and jumps to them, and to change the debugger data
which relates to these writes.


    Michael

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