Re: [PATCH v2 02/13] regcache: Add functions suitable for regset_supply/collect.

[Omair Javaid <omair dot javaid at linaro dot org>]

On 25 June 2014 21:48, Andreas Arnez <arnez@linux.vnet.ibm.com> wrote:
> These functions are intended to suit all targets that don't require too
> special logic in their regset supply/collect methods.  Having such
> generic functions helps reducing target-specific complexity.
>
> gdb/
>         * regcache.c: Include "regset.h".
>         (regcache_supply_regset, regcache_collect_regset): New functions.
>         * regcache.h (struct regcache_map_entry): New structure.
>         (REGCACHE_MAP_SKIP_BYTES): New enum value.
>         (regcache_supply_regset, regcache_collect_regset): New prototypes.
> ---
>  gdb/regcache.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  gdb/regcache.h | 44 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 110 insertions(+)
>
> diff --git a/gdb/regcache.c b/gdb/regcache.c
> index 5ee90b0..78fd962 100644
> --- a/gdb/regcache.c
> +++ b/gdb/regcache.c
> @@ -30,6 +30,7 @@
>  #include "exceptions.h"
>  #include "remote.h"
>  #include "valprint.h"
> +#include "regset.h"
>
>  /*
>   * DATA STRUCTURE
> @@ -1068,6 +1069,71 @@ regcache_raw_collect (const struct regcache *regcache, int regnum, void *buf)
>    memcpy (buf, regbuf, size);
>  }
>
> +/* Supply register REGNUM from BUF to REGCACHE, using the register map
> +   in REGSET.  If REGNUM is -1, do this for all registers in
> +   REGSET.  */
> +
> +void
> +regcache_supply_regset (const struct regset *regset,
> +                       struct regcache *regcache,
> +                       int regnum, const void *buf, size_t size)
> +{
> +  const struct regcache_map_entry *map = regset->regmap;
> +  int offs = 0;
> +  int i, count;
> +
> +  for (i = 0; (count = map[i].count) != 0; i++)
> +    {
> +      int regno = map[i].regno;
> +
> +      if (regno == REGCACHE_MAP_SKIP_BYTES)
> +       offs += count;
> +      else
> +       for (; count--; regno++)
> +         {
> +           int new_offs = offs + regcache->descr->sizeof_register[regno];
> +
> +           if (new_offs <= size && (regnum == -1 || regnum == regno))
> +             regcache_raw_supply (regcache, regno,
> +                                  buf ? (const gdb_byte *) buf + offs
> +                                  : NULL);
> +           offs = new_offs;
> +         }
> +    }
> +}
> +
> +/* Collect register REGNUM from REGCACHE to BUF, using the register
> +   map in REGSET.  If REGNUM is -1, do this for all registers in
> +   REGSET.  */
> +
> +void
> +regcache_collect_regset (const struct regset *regset,
> +                        const struct regcache *regcache,
> +                        int regnum, void *buf, size_t size)
> +{
> +  const struct regcache_map_entry *map = regset->regmap;
> +  int offs = 0;
> +  int i, count;
> +
> +  for (i = 0; (count = map[i].count) != 0; i++)
> +    {
> +      int regno = map[i].regno;
> +
> +      if (regno == REGCACHE_MAP_SKIP_BYTES)
> +       offs += count;
> +      else
> +       for (; count--; regno++)
> +         {
> +           int new_offs = offs + regcache->descr->sizeof_register[regno];
> +
> +           if (new_offs <= size && (regnum == -1 || regnum == regno))
> +             regcache_raw_collect (regcache, regno,
> +                                   (gdb_byte *) buf + offs);
> +           offs = new_offs;
> +         }
> +    }
> +}
> +
>
>  /* Special handling for register PC.  */
>
> diff --git a/gdb/regcache.h b/gdb/regcache.h
> index 8423f57..73ee043 100644
> --- a/gdb/regcache.h
> +++ b/gdb/regcache.h
> @@ -147,6 +147,50 @@ extern void regcache_raw_supply (struct regcache *regcache,
>  extern void regcache_raw_collect (const struct regcache *regcache,
>                                   int regnum, void *buf);
>
> +/* Mapping between register numbers and offsets in a buffer, for use
> +   in the '*regset' functions below.  In an array of
> +   'regcache_map_entry' each element is interpreted like follows:
> +
> +   - If 'regno' is a register number: Map register 'regno' to the
> +     current offset (starting with 0) and increase the current offset
> +     by the register's size.  Repeat this with consecutive register
> +     numbers up to 'regno+count-1'.
> +
> +   - If 'regno' is REGCACHE_MAP_SKIP_BYTES: Add 'count' to the current
> +     offset.
> +
> +   - If count=0: End of the map.  */
> +
> +struct regcache_map_entry
> +{
> +  int count;
> +  int regno;
> +};
> +
> +/* Special value for the 'regno' field in the struct above.  */
> +
> +enum
> +  {
> +    REGCACHE_MAP_SKIP_BYTES = -1,
> +  };
> +
> +/* Transfer a set of registers (as described by REGSET) between
> +   REGCACHE and BUF.  If REGNUM == -1, transfer all registers
> +   belonging to the regset, otherwise just the register numbered
> +   REGNUM.  The REGSET's 'regmap' field must point to an array of
> +   'struct regcache_map_entry'.
> +
> +   These functions are suitable for the 'regset_supply' and
> +   'regset_collect' fields in a regset structure.  */
> +
> +extern void regcache_supply_regset (const struct regset *regset,
> +                                   struct regcache *regcache,
> +                                   int regnum, const void *buf,
> +                                   size_t size);
> +extern void regcache_collect_regset (const struct regset *regset,
> +                                    const struct regcache *regcache,
> +                                    int regnum, void *buf, size_t size);
> +
>
>  /* The type of a register.  This function is slightly more efficient
>     then its gdbarch vector counterpart since it returns a precomputed
> --
> 1.8.4.2
>

Is there a way around avoiding the loop in supply/collect where regnum
!= -1? It should be more efficient in cases where we are looking for a
register with regnum > 0.