Re: [PATCH 02/12] fbsd-nat: Add helper routines for register sets using PT_[G]SETREGSET.

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

On 3/23/22 21:00, John Baldwin wrote:
> FreeBSD's kernel has recently added PT_GETREGSET and PT_SETREGSET
> operations to fetch a register set named by an ELF note type.  These
> helper routines provide helpers to check for a register set's
> existence, fetch registers for a register set, and store registers to
> a register set.
> ---
>   gdb/fbsd-nat.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   gdb/fbsd-nat.h | 42 +++++++++++++++++++++++++++++
>   2 files changed, 114 insertions(+)
> 
> diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
> index 934fdbad6ef..84abdd9a322 100644
> --- a/gdb/fbsd-nat.c
> +++ b/gdb/fbsd-nat.c
> @@ -1772,6 +1772,78 @@ fbsd_nat_target::store_register_set (struct regcache *regcache, int regnum,
>     return false;
>   }
>   
> +#ifdef PT_GETREGSET

Instead of ifdef-ing the entire block of code, wouldn't it be better to 
conditionally define the constant and have the code do checks at runtime?

If GDB is built on a machine without the proper headers and copied onto 
a machine with support for PT_GETREGSET, it won't be able to use this 
improvement. On the other hand, if we build GDB on a machine with the 
headers, but copy it into a machine without support for PT_GETREGSET, 
things will break, no?

> +/* See fbsd-nat.h.  */
> +
> +bool
> +fbsd_nat_target::have_regset (ptid_t ptid, int note)
> +{
> +  pid_t pid = get_ptrace_pid (ptid);
> +  struct iovec iov;
> +
> +  iov.iov_base = nullptr;
> +  iov.iov_len = 0;
> +  if (ptrace (PT_GETREGSET, pid, (PTRACE_TYPE_ARG3) &iov, note) == -1)
> +    return 0;
> +  return iov.iov_len;
> +}
> +
> +/* See fbsd-nat.h.  */
> +
> +bool
> +fbsd_nat_target::fetch_regset (struct regcache *regcache, int regnum, int note,
> +			       const struct regset *regset, void *regs,
> +			       size_t size)
> +{
> +  const struct regcache_map_entry *map
> +    = (const struct regcache_map_entry *) regset->regmap;
> +  pid_t pid = get_ptrace_pid (regcache->ptid ());
> +
> +  if (regnum == -1 || regcache_map_supplies (map, regnum, regcache->arch(),
> +					     size))
> +    {
> +      struct iovec iov;
> +
> +      iov.iov_base = regs;
> +      iov.iov_len = size;
> +      if (ptrace (PT_GETREGSET, pid, (PTRACE_TYPE_ARG3) &iov, note) == -1)
> +	perror_with_name (_("Couldn't get registers"));
> +
> +      regcache->supply_regset (regset, regnum, regs, size);
> +      return true;
> +    }
> +  return false;
> +}
> +
> +bool
> +fbsd_nat_target::store_regset (struct regcache *regcache, int regnum, int note,
> +			       const struct regset *regset, void *regs,
> +			       size_t size)
> +{
> +  const struct regcache_map_entry *map
> +    = (const struct regcache_map_entry *) regset->regmap;
> +  pid_t pid = get_ptrace_pid (regcache->ptid ());
> +
> +  if (regnum == -1 || regcache_map_supplies (map, regnum, regcache->arch(),
> +					     size))
> +    {
> +      struct iovec iov;
> +
> +      iov.iov_base = regs;
> +      iov.iov_len = size;
> +      if (ptrace (PT_GETREGSET, pid, (PTRACE_TYPE_ARG3) &iov, note) == -1)
> +	perror_with_name (_("Couldn't get registers"));
> +
> +      regcache->collect_regset (regset, regnum, regs, size);
> +
> +      if (ptrace (PT_SETREGSET, pid, (PTRACE_TYPE_ARG3) &iov, note) == -1)
> +	perror_with_name (_("Couldn't write registers"));
> +      return true;
> +    }
> +  return false;
> +}
> +#endif
> +
>   /* See fbsd-nat.h.  */
>   
>   bool
> diff --git a/gdb/fbsd-nat.h b/gdb/fbsd-nat.h
> index 82f7ee47949..6a4003627e4 100644
> --- a/gdb/fbsd-nat.h
> +++ b/gdb/fbsd-nat.h
> @@ -151,6 +151,19 @@ class fbsd_nat_target : public inf_ptrace_target
>     bool store_register_set (struct regcache *regcache, int regnum, int fetch_op,
>   			   int store_op, const struct regset *regset,
>   			   void *regs, size_t size);
> +
> +#ifdef PT_GETREGSET
> +  /* Helper routines which use PT_GETREGSET and PT_SETREGSET for the
> +     specified NOTE instead of regset-specific fetch and store
> +     ops.  */
> +
> +  bool fetch_regset (struct regcache *regcache, int regnum, int note,
> +		     const struct regset *regset, void *regs, size_t size);
> +
> +  bool store_regset (struct regcache *regcache, int regnum, int note,
> +		     const struct regset *regset, void *regs, size_t size);
> +#endif
> +
>   protected:
>     /* Wrapper versions of the above helpers which accept a register set
>        type such as 'struct reg' or 'struct fpreg'.  */
> @@ -172,6 +185,35 @@ class fbsd_nat_target : public inf_ptrace_target
>       return store_register_set (regcache, regnum, fetch_op, store_op, regset,
>   			       &regs, sizeof (regs));
>     }
> +
> +#ifdef PT_GETREGSET
> +  /* Helper routine for use in read_description in subclasses.  This
> +     routine checks if the register set for the specified NOTE is
> +     present for a given PTID.  If the register set is present, the
> +     the size of the register set is returned.  If the register set is
> +     not present, zero is returned.  */
> +
> +  bool have_regset (ptid_t ptid, int note);
> +
> +  /* Wrapper versions of the PT_GETREGSET and PT_REGSET helpers which
> +     accept a register set type.  */
> +
> +  template <class Regset>
> +  bool fetch_regset (struct regcache *regcache, int regnum, int note,
> +		     const struct regset *regset)
> +  {
> +    Regset regs;
> +    return fetch_regset (regcache, regnum, note, regset, &regs, sizeof (regs));
> +  }
> +
> +  template <class Regset>
> +  bool store_regset (struct regcache *regcache, int regnum, int note,
> +		     const struct regset *regset)
> +  {
> +    Regset regs;
> +    return store_regset (regcache, regnum, note, regset, &regs, sizeof (regs));
> +  }
> +#endif
>   };
>   
>   /* Fetch the signal information for PTID and store it in *SIGINFO.