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Re: varobj's find_frame_addr_in_frame_chain hack (and other ARM unwind notes)


On Mon, Jun 30, 2003 at 08:37:28PM -0400, Andrew Cagney wrote:
> >On Mon, Jun 30, 2003 at 03:04:42PM -0400, Andrew Cagney wrote:
> >
> >>>varobj.c:find_frame_addr_in_frame_chain, and mi-var-display.exp.  We 
> >>print
> >>>out $fp, and use then search for that value in the frame chain.  Well,
> >>>the DWARF-2 CFA value on ARM is biased from the frame pointer register,
> >>>generally by four bytes.  I chose to use the same thing in the prologue
> >>>unwinder for consistency - it makes unwinding ARM_SP_REGNUM simpler, 
> >>which
> >>>we need to get right in order for dummy frames to work.
> >
> >>
> >>Two wrongs, and they don't make a right :-(
> >>
> >>- the arm shouldn't be setting / forcing FP_REGNUM
> >>Instead, "fp" should always be the frame base.
> >
> >
> >$fp refers to a particular register on ARM.  Are you saying that print
> >$fp should print the frame base, and not the contents of the frame
> >pointer register?  Personally I'd find that pretty surprising.  Sure,
> >call it $frame if you want, but $fp is expected to be $r11 (in ARM
> >mode).
> 
> If the ISA has a register called $fp then $fp prints that register's 
> value, else, $fp prints the `frame base' (which should be `frame locals 
> address').  There's also a change-request open for someone to check that 
> the Arm really does follow this behavior (compare `info registers fp' 
> with `print $fp').
> 
> Anyway, the upshot is that, for scripting purposes, $fp is useless.
> 
> There is my patch to add $frame or $gdb.frame kicking around.
> 
> >>- the test shouldn't be using $fp to re-find a frame
> >>It should be using a frame ID, but that involves interface changes to 
> >>the MI -> MI 4.
> 
> >So.... what, should I just ignore the failure or should I make the
> >get_frame_base_address change?
> 
> Unless you're up to revamping the MI interface so that it takes frame 
> IDs ... :-).

Maybe after I'm done with the rest of this TODO list :-)  They tell me
it has a bottom somewhere in Timbuktu.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer


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