[LLVMdev] Preliminary patch for GDB support for JIT
echristo at apple.com
Wed Jul 8 12:16:40 PDT 2009
On Jul 8, 2009, at 11:41 AM, Reid Kleckner wrote:
> Right now, GDB has no way to be told about JITed code. I'm working on
> adding such an interface, and the LLVM JIT would be the first client.
> The interface is evolving, and I'll admit that right now it's
> downright terrible. Here's how it works right now:
> - The JIT generates the machine code and DWARF call frame info
> (.eh_frame/.debug_frame) for a function into memory.
> - The JIT copies that info into a temporary ELF file with a symbol for
> the function.
> - The JIT stuffs the filename and text address (function start) into a
> global struct at a special symbol that GDB knows about.
> - The JIT calls a function marked noinline that GDB knows about and
> has put an internal breakpoint in.
> - GDB takes control when the breakpoint fires, reads the filename and
> addr from the struct, and does the equivalent of an 'add-symbol-file'
> command from the prompt with those two arguments.
> - The JIT continues, and the next time we stop the program, we are
> able to produce a proper backtrace.
I've been thinking about this lately myself and this is along the
was going as well.
> For reference, here is the corresponding patch against GDB:
This appears to be missing some hunks...
> And finally, the patch to LLVM is attached and uploaded to Rietveld:
In general I'd like to see the ELF support separated from the main
interface. It makes any other platform support require a complete
> I know this code is sketchy and preliminary, but it's useful for us,
> and I have plans to improve it:
I'm not entirely sure about the lazy debug symbols part, but
as far as I can tell neither are you :)
The rest of it seems reasonable to me.
Note that I can't approve the patch anyhow :)
More information about the llvm-dev