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prototyping linux kernel-side gdbstub for userspace

Hi -

I'm slowly assembling a prototype gdb stub for debugging user-space
programs, based on utrace, for possible eventual inclusion in the
linux kernel.  For the moment, it is a toy alternative to ptrace() for
targeting existing processes, and it's not done even for that.  But
before too long though it should be able to use uprobes (q.v.) as a
kernel-side breakpointing facility using the Z packets, and maybe even
support agent expressions, multithreaded processes, and multiprocess

Only very basic parts work right now:

% gdb foobar
(gdb) target remote /proc/<pid>/gdb
     (due to suspected utrace bug, must currently manually interrupt the <pid> to get its attention)
#0 ... (backtrace works) ...
#1 ...
(gdb) p expression
# works
(gdb) set expression=value
# appears to work
(gdb) info regs
# appears to work - x86 and x86-64 only
(gdb) continue
# appears to work

But several things don't:
* signal injection
* other architectures
* proper fork/exec handling

Logistically, this is a patch added onto Roland McGrath's utrace git
tree over at


and build enabling CONFIG_UTRACE and CONFIG_UTRACE_GDB.  I'm planning
to continue working on it until the "several things don't" list above
is done.  I'd appreciate any help such as advising, porting, or code
such as on the future extensions listed way above.

- FChE

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