Hi!

I've been working on easing JIT interaction with GDB. The current
situation of generating ELF files in memory is usually too much work for
existing JIT compilers; especially since they don't otherwise contain
the ELF / DWARF manipulation routines (as opposed to a more traditional
compiler).

One way to solve this (which is what the attached patches try to do) is
to have the JIT vendor themselves decide on a "format" for the debug
info. Then the JIT compiler can register the debug info objects by
calling `__jit_debug_register_code', and also provide a shared object
that can be loaded and used to parse the emitted debug info.

With the current patch, the JIT compiler writers can create an SO which
implements the interface defined in `jit-reader.h', and call GDB with
`JIT_DEBUG_READER' set to the SO to load as the debug info reader.

The current version only allows the JIT debug info reader to parse out
some minimal amount of information, which will then allow GDB to display
a meaningful stack trace. The idea is that in case the user wants to use
GDB for full fledged debugging of generated code, it is probably better
to bite the bullet and generate DWARF.

I've done some preliminary testing by writing a debug info emitter and
reader for a Javascript VM; and things seem to work. I have attached the
patches for general comments and review.

Thanks!

-- 
Sanjoy Das
http://playingwithpointers.com