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

Kevin Buettner
2018-11-18T06:35:56Z

Hi John,

See my comments inline with your patch, below.

On Mon, 12 Nov 2018 10:17:21 +0100
John Darrington <john@darrington.wattle.id.au> wrote:

> Make gdb aware of the return values of functions which
> return in registers.
>
> 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.

> diff --git a/gdb/s12z-tdep.c b/gdb/s12z-tdep.c
> index bd0bd7c001..3da88523f7 100644
> --- a/gdb/s12z-tdep.c
> +++ b/gdb/s12z-tdep.c
> @@ -37,7 +37,9 @@
> #define N_PHYSICAL_REGISTERS (S12Z_N_REGISTERS - 2)
>
>
> -/* A permutation of all the physical registers. */
> +/* A permutation of all the physical registers. Indexing this array
> + with an integer from gdb's internal representation will return the
> + register enum. */
> static const int reg_perm[N_PHYSICAL_REGISTERS] =
> {
> REG_D0,
> @@ -55,6 +57,16 @@ static const int reg_perm[N_PHYSICAL_REGISTERS] =
> REG_CCW
> };
>
> +/* The inverse of the above permutation. Indexing this
> + array with a register enum (e.g. REG_D2) will return the register
> + number in gdb's internal representation. */
> +static const int inv_reg_perm[N_PHYSICAL_REGISTERS] =
> + {
> + 2, 3, 4, 5, /* d2, d3, d4, d5 */
> + 0, 1, /* d0, d1 */
> + 6, 7, /* d6, d7 */
> + 8, 9, 10, 11, 12 /* x, y, s, p, ccw */
> + };

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.

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.

> /* 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.

Kevin