Re: [PATCH v2 22/24] gdb: migrate arm to gdbarch_pseudo_register_read_value

[Luis Machado <luis.machado@arm.com>]

On 11/24/23 21:26, Simon Marchi wrote:
> Make arm use the "newer" gdbarch_pseudo_register_read_value.  This fixes
> reading pseudo registers in non-current frames on that architecture.
> 
> Change-Id: Ic4d3d5d96957a4addfa3443c7b567dc4a31794a9
> Reviewed-By: John Baldwin <jhb@FreeBSD.org>
> ---
>  gdb/arm-tdep.c | 76 +++++++++++++++++++++++++++++---------------------
>  1 file changed, 44 insertions(+), 32 deletions(-)
> 
> diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
> index 13c9ca6761da..cded66c91454 100644
> --- a/gdb/arm-tdep.c
> +++ b/gdb/arm-tdep.c
> @@ -9816,61 +9816,73 @@ arm_neon_quad_read (struct gdbarch *gdbarch, readable_regcache *regcache,
>    return REG_VALID;
>  }
>  
> -/* Read the contents of the MVE pseudo register REGNUM and store it
> -   in BUF.  */
> +/* Read the contents of a NEON quad register, by reading from two double
> +   registers, and return it as a value.  QUAD_REG_INDEX is the index of the quad
> +   register, in [0, 15].  */
>  
> -static enum register_status
> -arm_mve_pseudo_read (struct gdbarch *gdbarch, readable_regcache *regcache,
> -		     int regnum, gdb_byte *buf)
> +static value *
> +arm_neon_quad_read_value (gdbarch *gdbarch, frame_info_ptr next_frame,
> +			  int pseudo_reg_num, int quad_reg_index)
> +{
> +  std::string raw_reg_name = string_printf ("d%d", quad_reg_index << 1);
> +  int double_regnum
> +    = user_reg_map_name_to_regnum (gdbarch, raw_reg_name.c_str (),
> +				   raw_reg_name.length ());
> +
> +  return pseudo_from_concat_raw (next_frame, pseudo_reg_num, double_regnum,
> +				 double_regnum + 1);
> +}
> +
> +/* Read the contents of the MVE pseudo register REGNUM and return it as a
> +   value.  */
> +static value *
> +arm_mve_pseudo_read_value (gdbarch *gdbarch, frame_info_ptr next_frame,
> +			   int pseudo_reg_num)
>  {
>    arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
>  
>    /* P0 is the first 16 bits of VPR.  */
> -  return regcache->raw_read_part (tdep->mve_vpr_regnum, 0, 2, buf);
> +  return pseudo_from_raw_part (next_frame, pseudo_reg_num,
> +			       tdep->mve_vpr_regnum, 0);
>  }
>  
> -static enum register_status
> -arm_pseudo_read (struct gdbarch *gdbarch, readable_regcache *regcache,
> -		 int regnum, gdb_byte *buf)
> +static value *
> +arm_pseudo_read_value (gdbarch *gdbarch, frame_info_ptr next_frame,
> +		       const int pseudo_reg_num)
>  {
> -  const int num_regs = gdbarch_num_regs (gdbarch);
> -  char name_buf[4];
> -  gdb_byte reg_buf[8];
> -  int offset, double_regnum;
>    arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
>  
> -  gdb_assert (regnum >= num_regs);
> +  gdb_assert (pseudo_reg_num >= gdbarch_num_regs (gdbarch));
>  
> -  if (is_q_pseudo (gdbarch, regnum))
> +  if (is_q_pseudo (gdbarch, pseudo_reg_num))
>      {
>        /* Quad-precision register.  */
> -      return arm_neon_quad_read (gdbarch, regcache,
> -				 regnum - tdep->q_pseudo_base, buf);
> +      return arm_neon_quad_read_value (gdbarch, next_frame, pseudo_reg_num,
> +				       pseudo_reg_num - tdep->q_pseudo_base);
>      }
> -  else if (is_mve_pseudo (gdbarch, regnum))
> -    return arm_mve_pseudo_read (gdbarch, regcache, regnum, buf);
> +  else if (is_mve_pseudo (gdbarch, pseudo_reg_num))
> +    return arm_mve_pseudo_read_value (gdbarch, next_frame, pseudo_reg_num);
>    else
>      {
> -      enum register_status status;
> +      int s_reg_index = pseudo_reg_num - tdep->s_pseudo_base;
>  
> -      regnum -= tdep->s_pseudo_base;
>        /* Single-precision register.  */
> -      gdb_assert (regnum < 32);
> +      gdb_assert (s_reg_index < 32);
>  
>        /* s0 is always the least significant half of d0.  */
> +      int offset;
>        if (gdbarch_byte_order (gdbarch) == BFD_ENDIAN_BIG)
> -	offset = (regnum & 1) ? 0 : 4;
> +	offset = (s_reg_index & 1) ? 0 : 4;
>        else
> -	offset = (regnum & 1) ? 4 : 0;
> +	offset = (s_reg_index & 1) ? 4 : 0;
>  
> -      xsnprintf (name_buf, sizeof (name_buf), "d%d", regnum >> 1);
> -      double_regnum = user_reg_map_name_to_regnum (gdbarch, name_buf,
> -						   strlen (name_buf));
> +      std::string raw_reg_name = string_printf ("d%d", s_reg_index >> 1);
> +      int double_regnum
> +	= user_reg_map_name_to_regnum (gdbarch, raw_reg_name.c_str (),
> +				       raw_reg_name.length ());
>  
> -      status = regcache->raw_read (double_regnum, reg_buf);
> -      if (status == REG_VALID)
> -	memcpy (buf, reg_buf + offset, 4);
> -      return status;
> +      return pseudo_from_raw_part (next_frame, pseudo_reg_num, double_regnum,
> +				   offset);
>      }
>  }
>  
> @@ -10905,7 +10917,7 @@ arm_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>    if (tdep->have_s_pseudos || have_mve || have_pacbti)
>      {
>        set_gdbarch_num_pseudo_regs (gdbarch, num_pseudos);
> -      set_gdbarch_pseudo_register_read (gdbarch, arm_pseudo_read);
> +      set_gdbarch_pseudo_register_read_value (gdbarch, arm_pseudo_read_value);
>        set_gdbarch_deprecated_pseudo_register_write (gdbarch, arm_pseudo_write);
>      }
>  

LGTM.

Approved-by: Luis Machado <luis.machado@arm.com>