jacob navia writes:
> Hi
>
> Context:
>
> I am writing a JIT and need to register the frame information about
> the generated program within the context of a larger C++ program
> compiled with g++. Stack layout is like this:
>
> catch established by C++
> JITTED code generated dynamically
> JITTED code
> JITTED code calls a C++ routine
> C++ routine calls other C++ routines
> C++ routine makes a THROW
>
> The throw must go past the JITTED code to the established C++ catch.
>
> Problem.
>
> The stack unwinder stops with END_OF_STACK at the Jitted code. Why?
> Following the code with the debugger I see that the unwider looks
> for the next frame using the structures established by the dynamic loader,
> specifically in the function "__dl_iterate_phdr" in the file
> "dl-iteratephdr.c" in the glibc.
>
> So, this means:
>
> 1) I am cooked and what I want to do is impossible. This means I will
> probably
> get cooked at work for proposing something stupid like this :-)
>
> 2) There is an API or a way of adding at run time a routine to the lists
> of loaded objects in the same way as the dynamic loader does.
>
> PLEEEEEEZE do not answer with:
>
> "Just look at the code of the dynamic loader!"
>
> because I have several megabytes of code to understand already!!!!!!!!!
>
> I am so near the end that it would be a shame to stop now. My byte
> codes for the DWARF interpreter LOAD into the interpreter
> successfully, and they are executed OK, what has costed me several
> weeks of efforts, wading through MBs of code and missing/wrong
> specs.
>
> I just would like to know a way of registering (and deregistering
> obviously) code that starts at address X and is Y bytes long. JUst
> that.
The way you do not reply to mails replying to your questions doesn't
encourage people to help you. Please try harder to answer.
I suspect that the gcc unwinder is relying on __dl_iterate_phdr to
scan the loaded libraries and isn't using the region that you have
registered.
But this is odd, becasue when I look at _Unwind_Find_FDE in
unwind-dw2-fde-glibc.c, I see:
ret = _Unwind_Find_registered_FDE (pc, bases);
...
if (dl_iterate_phdr (_Unwind_IteratePhdrCallback, &data) < 0)
return NULL;
So, it looks to me as though we do call _Unwind_Find_registered_FDE
first. If you have registered your EH data, it should be found.
So, what happens when _Unwind_Find_registered_FDE is called? Does it
find the EH data you have registered?
Andrew.
