Re: jit interface and jit reader

[Tony Simpson <agjasimpson@gmail.com>]

Hi Frank,

I think I ran into the same problem a couple of years ago. I fixed my
problem here
https://github.com/tonysimpson/binutils-gdb/commits/jit-interface-fixes.

I've forgotten the details but I remember I got it working with my patch -
here is the commit message for 3c0e5d45f727d5ef98b681103954820c8fbbd700
Fixes:
  * Named blocks not appearing as functions - can't break on functions;
  * Pending breakpoints on JIT'd code not being resolved;
  * GDB goes into an infinit loop with more than one JIT block in a
     symtab;
  * Unwinder function not being called.

Hope this helps. Best Regards,

Tony

On Mon, 21 Jan 2019 at 13:53, Frank Tetzel <s1445051@mail.zih.tu-dresden.de>
wrote:

> > I have trouble getting GDB's jit interface to work. I'm trying to make
> > application using AsmJit [1] easier to debug by being able to break
> > when entering jitted code. As AsmJit is just an assembler returning a
> > function pointer to the generated code, I do not want to create an
> > object file for it. That is why I'm trying to use jit-reader, but the
> > symbol does not seem to show up in GDB and a pending breakpoint is
> > never hit.
> >
> > What am I doing wrong? I attached two files: gdbjit.cpp is talking to
> > GDB via the jit interface. gdbjit-reader.c is the jit reader for GDB
> > which I compile to a shared object and load in GDB with
> > jit-reader-load.
> >
> > It does not implement unwind and get_frame_id. Do I need these
> > functions? unwind is called sometimes. Is there a minimal example
> > somewhere which implements jit reader?
> >
> > [1] https://github.com/asmjit/asmjit
>
>
> I looked at GDB's source code a bit and found a minimal example in
> testsuite/gdb.base/jit{host.c,reader.c}.
>
> The problem is also visible there: I can follow the indirect call into
> the generated code. In TUI-mode, the instructions belonging to the
> function have the correct symbol+offset. backtrace shows the function
> name as well.
>
> But, I cannot set a breakpoint with the function name. Nor can I use
> the command disassemble, only the disassemble view in TUI works.
>
> How can I register the address range as a proper function?
>
> Best regards,
> Frank
>