Re: [RFA] Rewrite mips_get_saved_register()

[Kevin Buettner <kevinb@redhat.com>]

On Aug 9, 12:12pm, Andrew Cagney wrote:

> > This patch depends on the following (as of yet) unapproved patches:
> > 
> >     http://sources.redhat.com/ml/gdb-patches/2002-08/msg00189.html
> >     http://sources.redhat.com/ml/gdb-patches/2002-08/msg00195.html
> >     http://sources.redhat.com/ml/gdb-patches/2002-08/msg00196.html
> > 
> > Okay to commit?
> > 
> > 	* mips-tdep.c (mips_get_saved_register): Rewrite to use
> > 	frame_register_unwind() instead of find_saved_register().
> 
> Sorry, not like this.  Can you please, for the moment, just in-line the 
> call to find_saved_register().
> 
> (The two other bugs you fixed were definitly needed and thanks for 
> finding them.  How the code got away with not setting the SP I don't know.)
> 
> -      if (raw_buffer != NULL)
> - 
> {
> - 
>    LONGEST val;
> - 
>    if (regnum < 32)
> - 
>      /* Only MIPS_SAVED_REGSIZE bytes of GP registers are
> -               saved. */
> - 
>      val = read_memory_integer (addr, MIPS_SAVED_REGSIZE);
> - 
>    else
> - 
>      val = read_memory_integer (addr, REGISTER_RAW_SIZE (regnum));
> - 
>    store_address (raw_buffer, REGISTER_RAW_SIZE (regnum), val);
> - 
> }
> 
> In theory (and emphasis on the theory) things need to be changed so that:
> 
> - 32 32 bit nameless pseudo-registers are added to the cooked register space
> - the 32 64 bit gprs get given a 64 bit virtual type so that they have 
> identical raw and virtual sizes
> - The debug info, for a 32 bit ABI, maps the gpr register numbers onto 
> the 32 bit pseudo register range
> - The gdbarch pseudo register read/write function maps the 32 bit 
> pseudo-registers onto the 64 bit gprs.
> - For init saved regs, dependant on the size of the register saved, 
> either the the address of the 64 bit GPR or the address of the 32 bit 
> pseudo-register is set
> - a custom mips register unwind function maps the requested register (64 
> bit gpr or 32 bit pseudo) onto: the 32 bit pseudo, the 64 bit gpr, or a 
> further recursive unwind call.  If it has to do a 32/64 mapping then it 
> sets not-an-lval.
> - you find you have to yank all sorts of register converible code
> 
> But like I said, it is theory, the mips suffers from one hack (like the 
> above) piled on top of another (the register convertable stuff, the 
> register raw/virtual size being different, ...).  I don't know if now is 
> the time to be experimenting with theories :-)

Yes, fixing all of the above is quite a lot more work than I have time
for at the moment.

But, assuming that my rewrite is functionally equivalent to the
original, what is the reason for preferring to inline
find_saved_register() over using the new interface?

I should think that using frame_register_unwind() would:

    - allow it to be better tested.  E.g, I wouldn't have found
      the bugs that I did recently had I not gone through this
      exercise.
    - shorten the time needed to reexamine mips_get_saved_register()
      when it finally does come time to reimplement or eliminate it.

Kevin