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Re: multi-arch and CALL_DUMMY_BREAKPOINT_OFFSET
- From: Andrew Cagney <ac131313 at cygnus dot com>
- To: Richard dot Earnshaw at arm dot com
- Cc: gdb at sources dot redhat dot com
- Date: Sun, 10 Feb 2002 15:09:40 -0500
- Subject: Re: multi-arch and CALL_DUMMY_BREAKPOINT_OFFSET
- References: <200202081134.LAA07778@cam-mail2.cambridge.arm.com>
> I guess I'm going to find several things like this...
> Well it appears that in a multi-arch gdb (even at level 1),
> CALL_DUMMY_BREAKPOINT_OFFSET can only be a constant for any particular
> architecture. This is a problem, because on the ARM it is currently a
> function that returns one of two values depending on whether the
> call-dummy stub has to be ARM code or Thumb code. Note that both types of
> code can exist within a single application and it is not always safe to
> assume that every function is interworking safe.
Oops :-( People keep finding things I thought would be constant but are
not.
> I guess I could re-write the whole of the call-dummy stuff so that
> appropriate breakpoints are built in, but that is certainly going to be
> non-trivial.
>
> Any suggestions? Can I diddle with the gdbarch setting dynamically -- eg
> by calling gdbarch_set_call_dummy_breakpoint_offset() from within
> arm_fix_call_dummy()? It's quite gross, but it might work.
Two suggestions:
Replace CALL_DUMMY_BREAKPOINT_OFFSET and CALL_DUMMY_BREAKPOINT_OFFSET_P
with a predicate function (``F:'')? The predicate mechanism was only
added recently. I have a feeling that while this looks good, it isn't
as easy as it seems :-(
Introduce a new method (``f:'') that, for legacy code, uses
CALL_DUMMY_BREAKPOINT_OFFSET? Deprecate (ARI / bug report) the old
CALL_DUMMY_BREAKPOINT_OFFSET variable.
> Long term it would probably be better to rewrite the call-dummy handling
> to remove the covert variable that is used to communicate between the
> various call-dummy stubs, but I'd rather not do that now.
/* CALL_DUMMY is an array of words (REGISTER_SIZE), but each word
is in host byte order. Before calling FIX_CALL_DUMMY, we byteswap it
and remove any extra bytes which might exist because ULONGEST is
bigger than REGISTER_SIZE.
NOTE: This is pretty wierd, as the call dummy is actually a
sequence of instructions. But CISC machines will have
to pack the instructions into REGISTER_SIZE units (and
so will RISC machines for which INSTRUCTION_SIZE is not
REGISTER_SIZE).
NOTE: This is pretty stupid. CALL_DUMMY should be in strict
target byte order. */
You would not be alone.
Andrew