Re: [RFA] mips fp register display

[Daniel Jacobowitz <dmj+ at andrew dot cmu dot edu>]

On Thu, Jun 21, 2001 at 03:42:10PM -0700, Don Howard wrote:
> 
> This is a patch for an obscure mips fp register display problem.  32 bit mips
> chips support 64 bit float operations using two fp registers.  64 bit mips
> chips provide a backward compatiblity mode where 64 bit float ops are also
> supported using 2 float regsiters -- 32 bits stored in each of the 2 64bit fp
> regs.
> 
> This patch addresses insight as well as cli gdb.  Insight is not 100% correct:
> single precision floats are displayed in double format =( (cli gdb displays
> both float and double).  I can change REGISTER_VIRTUAL_TYPE() to try to guess
> the the intended type (builtin_type_{float,double}), but that is really not
> the right place to fix this problem.
> 
> 
> 2001-06-21  Don Howard  <dhoward@redhat.com>
> 
> 
>         * mips-tdep.c (mips2_read_fp_register): New function.  Reads a
>         64-bit float value stored as two 32-bit fragments in consecutive
>         float registers.
>         (mips2_fp_compat): New function.  Determine if a MIPS3 or later
>         cpu is operating in MIPS{1,2} float-compat mode.
>         (mips_get_saved_register): Modified to use new
>         mips2-compat float support.
>         (mips_print_register): Modified to display 64-bit float regs in
>         single and double precision.

I see why this is necessary, but it doesn't address the problem I was
talking about.  I also don't think it's really the right solution.
If you look a few lines higher in mips_print_register, you see:

  /* If an even floating point register, also print as double. */
  if (TYPE_CODE (REGISTER_VIRTUAL_TYPE (regnum)) == TYPE_CODE_FLT
      && !((regnum - FP0_REGNUM) & 1))
    if (REGISTER_RAW_SIZE (regnum) == 4)        /* this would be silly on MIPS64 or N32 (Irix 6) */
      { 
        char dbuffer[2 * MAX_REGISTER_RAW_SIZE];

        read_relative_register_raw_bytes (regnum, dbuffer);
        read_relative_register_raw_bytes (regnum + 1, dbuffer + MIPS_REGSIZE);
        REGISTER_CONVERT_TO_TYPE (regnum, builtin_type_double, dbuffer);

        printf_filtered ("(d%d: ", regnum - FP0_REGNUM);
        val_print (builtin_type_double, dbuffer, 0, 0,
                   gdb_stdout, 0, 1, 0, Val_pretty_default);
        printf_filtered ("); ");
      }
  fputs_filtered (REGISTER_NAME (regnum), gdb_stdout);

Well, obviously it's not always silly on N32.  Change the
	if (REGISTER_RAW_SIZE (regnum) == 4)
to something like
	if (mips_small_float_registers ())

On the other hand, I think that perhaps if FR is set
REGISTER_RAW_SIZE (regnum) ought to be 4.  Isn't that what it means?

Also, we already have REGISTER_CONVERT_TO_TYPE.  Rather than hacking in
a third or perhaps fourth copy of this sort of thing, why not extend
REGISTER_CONVERT_TO_TYPE?

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer