Re: [PATCH v2] gdb/csky support .reg2 for kernel 4.x and later

[Kevin Buettner via Gdb-patches <gdb-patches@sourceware.org>]

On Mon, 25 Jul 2022 10:44:59 +0800
Jiangshuai Li via Gdb-patches <gdb-patches@sourceware.org> wrote:

> When kernel's version >= 4.x, the size of .reg2 section will be 400.
> Contents of .reg2 are {
>     unsigned long vr[96]; // vr0~vr15 & fr16~fr31
>     unsigned long fcr;
>     unsigned long fesr;
>     unsigned long fid;
>     unsigned long reserved;
> };
>
> ---
>  gdb/csky-linux-tdep.c | 150 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 134 insertions(+), 16 deletions(-)
> 
> diff --git a/gdb/csky-linux-tdep.c b/gdb/csky-linux-tdep.c
> index 440045e7713..aa85a299922 100644
> --- a/gdb/csky-linux-tdep.c
> +++ b/gdb/csky-linux-tdep.c
> @@ -36,6 +36,8 @@
>  #define SIZEOF_CSKY_GREGSET 34*4
>  /* Float regset fesr fsr fr0-fr31 for CK810.  */
>  #define SIZEOF_CSKY_FREGSET 34*4
> +/* Float regset vr0~vr15 fr15~fr31, reserved for CK810 when kernel 4.x.  */

You might want to expand the comment above indicating that the struct
layout can be found in a comment within csky_supply_fregset.

> +#define SIZEOF_CSKY_FREGSET_K4X  400
>  
>  /* Offset mapping table from core_section to regcache of general
>     registers for ck810.  */
> @@ -118,15 +120,76 @@ csky_supply_fregset (const struct regset
> *regset, int fregset_num = ARRAY_SIZE (csky_fregset_offset);
>  
>    gdb_assert (len >= SIZEOF_CSKY_FREGSET);
> -  for (i = 0; i < fregset_num; i++)
> +  if (len == SIZEOF_CSKY_FREGSET)
>      {
> -      if ((regnum == csky_fregset_offset[i] || regnum == -1)
> -	  && csky_fregset_offset[i] != -1)
> -	{
> -	  int num = csky_fregset_offset[i];
> -	  offset += register_size (gdbarch, num);
> -	  regcache->raw_supply (csky_fregset_offset[i], fregs +
> offset);
> -	}
> +      for (i = 0; i < fregset_num; i++)
> +        {
> +          if ((regnum == csky_fregset_offset[i] || regnum == -1)
> +              && csky_fregset_offset[i] != -1)
> +            {
> +              int num = csky_fregset_offset[i];
> +              offset += register_size (gdbarch, num);
> +              regcache->raw_supply (csky_fregset_offset[i], fregs +
> offset);
> +            }
> +        }
> +    }
> +  else if (len == SIZEOF_CSKY_FREGSET_K4X)
> +    {
> +      /* When kernel version >= 4.x, .reg2 size will be 400.
> +         Contents is {
> +           unsigned long vr[96]; // vr0~vr15 + fr16~fr31
> +           unsigned long fcr;
> +           unsigned long fesr;
> +           unsigned long fid;
> +           unsigned long reserved;
> +         }  */
> +      int fcr_regno[] = {122, 123, 121}; /* fcr, fesr, fid.  */
> +
> +      /* Supply vr0~vr15.  */
> +      for (i = 0; i < 16; i ++)
> +        {
> +          if (gdbarch_register_name (gdbarch, (CSKY_VR0_REGNUM + i)))
> +            {
> +              offset = 16 * i;
> +              regcache->raw_supply (CSKY_VR0_REGNUM + i,
> +                                    fregs + offset);
> +            }
> +        }
> +      /* Supply fr0~fr15.  */
> +      for (i = 0; i < 16; i ++)
> +        {
> +          if (gdbarch_register_name (gdbarch, (CSKY_FR0_REGNUM + i)))
> +            {
> +              offset = 16 * i;

Are these offsets correct?  I.e. do the fr0~fr15 registers use
the same offsets as vr0~vr15?

Also, not related to this patch, but while trying to figure this out,
I found this line in csky-tdep.h - it looks fishy to me since it's
way bigger than CSKY_MAX_REGS:

  CSKY_FR16_REGNUM = 1172,

It definitely matters since you refer to CSKY_FR16_REGNUM below.

> +              regcache->raw_supply (CSKY_FR0_REGNUM + i,
> +                                    fregs + offset);
> +            }
> +        }
> +      /* Supply fr16~fr31.  */
> +      for (i = 0; i < 16; i ++)
> +        {
> +          if (gdbarch_register_name (gdbarch, (CSKY_FR16_REGNUM +
> i)))
> +            {
> +              offset = (16 * 16) + (8 * i);
> +              regcache->raw_supply (CSKY_FR16_REGNUM + i,
> +                                    fregs + offset);
> +            }
> +        }
> +     /* Supply fcr, fesr, fid.  */
> +      for (i = 0; i < 3; i ++)
> +        {
> +          if (gdbarch_register_name (gdbarch, fcr_regno[i]))
> +            {
> +              offset = (16 * 16) + (16 * 8) + (4 * i);
> +              regcache->raw_supply (fcr_regno[i],
> +                                    fregs + offset);
> +            }
> +        }
> +    }
> +  else
> +    {
> +      warning (_("Unknow size %ld of section .reg2, can not get
> value"
> +                 " of float registers."), len);
>      }
>  }
>  
> @@ -144,14 +207,66 @@ csky_collect_fregset (const struct regset
> *regset, int offset = 0;
>  
>    gdb_assert (len >= SIZEOF_CSKY_FREGSET);
> -  for (regno = 0; regno < fregset_num; regno++)
> +  if (len == SIZEOF_CSKY_FREGSET)
> +    {
> +      for (regno = 0; regno < fregset_num; regno++)
> +        {
> +          if ((regnum == csky_fregset_offset[regno] || regnum == -1)
> +               && csky_fregset_offset[regno] != -1)
> +            {
> +              offset += register_size (gdbarch,
> csky_fregset_offset[regno]);
> +              regcache->raw_collect (regno, fregs + offset);
> +            }
> +        }
> +    }
> +  else if (len == SIZEOF_CSKY_FREGSET_K4X)
> +    {
> +      /* When kernel version >= 4.x, .reg2 size will be 400.
> +         Contents is {
> +           unsigned long vr[96]; // vr0~vr15 + fr16~fr31
> +           unsigned long fcr;
> +           unsigned long fesr;
> +           unsigned long fid;
> +           unsigned long reserved;
> +         }  */
> +      int i = 0;
> +      int fcr_regno[] = {122, 123, 121}; /* fcr, fesr, fid.  */
> +
> +      /* Supply vr0~vr15.  */
> +      for (i = 0; i < 16; i ++)
> +        {
> +          if (gdbarch_register_name (gdbarch, (CSKY_VR0_REGNUM + i)))
> +            {
> +              offset = 16 * i;
> +              regcache ->raw_collect (CSKY_VR0_REGNUM + i,
> +                                      fregs + offset);
> +            }
> +        }
> +      /* Supply fr16~fr31.  */
> +      for (i = 0; i < 16; i ++)
> +        {
> +          if (gdbarch_register_name (gdbarch, (CSKY_FR16_REGNUM +
> i)))
> +            {
> +              offset = (16 * 16) + (8 * i);
> +              regcache ->raw_collect (CSKY_FR16_REGNUM + i,
> +                                      fregs + offset);
> +            }
> +        }
> +      /* Supply fcr, fesr, fid.  */
> +      for (i = 0; i < 3; i ++)
> +        {
> +          if (gdbarch_register_name (gdbarch, fcr_regno[i]))
> +            {
> +              offset = (16 * 16) + (16 * 8) + (4 * i);
> +              regcache ->raw_collect (fcr_regno[i],
> +                                      fregs + offset);
> +            }
> +        }
> +    }
> +  else
>      {
> -      if ((regnum == csky_fregset_offset[regno] || regnum == -1)
> -	  && csky_fregset_offset[regno] != -1)
> -	{
> -	  offset += register_size (gdbarch,
> csky_fregset_offset[regno]);
> -	  regcache->raw_collect (regno, fregs + offset);
> -	}
> +      warning (_("Unknow size %ld of section .reg2, will not set
> value"
> +                 " of float registers."), len);
>      }
>  }
>  
> @@ -166,7 +281,10 @@ static const struct regset csky_regset_float =
>  {
>    NULL,
>    csky_supply_fregset,
> -  csky_collect_fregset
> +  csky_collect_fregset,
> +  /* Allow .reg2 has different size, buf size of .reg2 should
> +     always is or bigger than SIZEOF_CSKY_FREGSET.  */

I recommend a slightly different wording for the above comment:

     /* Allow .reg2 to have a different size, but the size of .reg2 should
        always be bigger than SIZEOF_CSKY_FREGSET.  */

> +  1
>  };
>  
>  /* Iterate over core file register note sections.  */
> -- 
> 2.25.1
>