[PATCH 1/1] [RFC] gdb: corelow: make possible to modify (set) registers for a corefile

[Ulrich Weigand]

Roman Pen wrote:

> Despite the fact that this is a hairy hack this change eases debugging
> of a jmp_buf (setjmp()) and user contexts (makecontext()), which are
> highly used in QEMU project as a part of coroutines.
> 
> This change allows setting registers for a corefile, thus QEMU gdb
> script (qemu/scripts/qemugdb/coroutine.py) is allowed to investigate
> backtrace of a preempted coroutine context.  Previously only debugging
> of a live process was allowed.
> 
> This patch caches all register on a first attempt to modify register
> '(gdb) set $REG = ADDR' and then cached copy is always returned from
> get_core_registers().
> 
> This change should not break previous behaviour if nobody sets any
> register, i.e. on each get_core_registers() call registers from a
> corefile will be reread.

I'm wondering why you need that extra copy of the registers;
there already should be a regcache that would be able to hold
any modified values.

It is not currently possible to actually change those values
in the regcache because there is no to_store_registers routine.
But simply adding such a routine that does nothing (just like
to_prepare_to_store in your patch) should hopefully be enough ...

In any case, it would be good to add or extend a test case to
verify that this feature is working as intended.

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU/Linux compilers and toolchain
  Ulrich.Weigand@de.ibm.com