Re: [PATCH 2/2] GDB: S12Z: new function s12z_extract_return_value

[John Darrington <john@darrington.wattle.id.au>]

Hi Kevin,

Thanks for the review.

On Sat, Nov 17, 2018 at 11:35:50PM -0700, Kevin Buettner wrote:
     > 
     > gdb/ChangeLog:
     > * s12z-tdep.c (s12z_extract_return_value): New function.
     >   (inv_reg_perm) New array.
     >   (s12z_return_value): Populate readbuf if non-null.
     
     Make sure that this is indented correctly when it eventually goes
     in the ChangeLog file.

Is it documented anywhere what "correctly" means?
     
     My two cents on all of the above...
     
     I think you'll have a lot less grief with this architecture port if
     you don't try to use the numbering defined in include/opcode/s12z.h. 
     Create a new numbering with new constants for GDB's purposes ordered
     as shown in the reg_perm array.  Then use these constants in place of
     the various REG_ constants that are currently in s12z-tdep.c.  If you
     still want to be able to access registers[], it may make sense to
     have an array which maps GDB's constants to those in include/opcode.

I'm beginning to think that you're right here.  I may change it in the
way you propose in a future patch.
     
     Also, if you want CCH and CCL to be show in "info registers" and/or
     allow the user to display and set them, these can be implemented via
     the use of pseudo-registers.

A the moment, I don't think it's worth bothering about.  CCH and CCL are
merely the high and low bytes of a 16bit register CCW.   The names CCH
and CCL only exist because of two (rarely used) instructions in the ISA.
     
     >  /*  Return the name of the register REGNUM.  */
     >  static const char *
     > @@ -467,11 +479,59 @@ s12z_print_registers_info (struct gdbarch *gdbarch,
     >  
     >  \f
     >  
     > +
     > +static void
     > +s12z_extract_return_value (struct type *type, struct regcache *regcache,
     > +                              void *valbuf)
     > +{
     > +  int reg = -1;
     > +
     > +  gdb_byte buf[4];
     > +
     > +  switch (TYPE_LENGTH (type))
     > +    {
     > +    case 0:   /* Nothing to do */
     > +      return;
     > +
     > +    case 1:
     > +      reg = REG_D0;
     > +      break;
     > +
     > +    case 2:
     > +      reg = REG_D2;
     > +      break;
     > +
     > +    case 3:
     > +      reg = REG_X;
     > +      break;
     > +
     > +    case 4:
     > +      reg = REG_D6;
     > +      break;
     > +
     > +    default:
     > +      error (_("bad size for return value"));
     > +      return;
     > +    }
     > +
     > +  regcache->cooked_read (inv_reg_perm[reg], buf);
     > +  memcpy (valbuf, buf, TYPE_LENGTH (type));
     
     Is there any reason not to just pass valbuf in place of buf to
     cooked_read?  Doing so will get rid of the memcpy.

Probably not.  Thanks for noticing this.
     
J'

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