RE: [PATCH v2] gdbserver: dump 'xx...x' in collect_register_as_string for unavailable register

["Aktemur, Tankut Baris" <tankut.baris.aktemur@intel.com>]

On Friday, November 24, 2023 12:22 PM, Luis Machado wrote:
> 
> Hi,
> 
> On 11/21/23 19:53, Aktemur, Tankut Baris wrote:
> > Kindly pinging.
> >
> > Regards
> > -Baris
> >
> > On Tuesday, June 20, 2023 5:55 PM, Aktemur, Tankut Baris wrote:
> >> Fix 'collect_register_as_string' so that unavailable registers are
> >> dumped as 'xx...x' instead of arbitrary values.  This gives the
> >> opportunity that we can reuse 'collect_register_as_string' in
> >> 'registers_to_string' for additional code simplification.
> >> ---
> >>  gdbserver/regcache.cc | 26 +++++++++++---------------
> >>  1 file changed, 11 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/gdbserver/regcache.cc b/gdbserver/regcache.cc
> >> index 0b1141662ac..c0a6d6eb0a4 100644
> >> --- a/gdbserver/regcache.cc
> >> +++ b/gdbserver/regcache.cc
> >> @@ -210,24 +210,13 @@ find_register_by_number (const struct target_desc *tdesc, int
> >> n)
> >>  void
> >>  registers_to_string (struct regcache *regcache, char *buf)
> >>  {
> >> -  unsigned char *registers = regcache->registers;
> >>    const struct target_desc *tdesc = regcache->tdesc;
> >>
> >>    for (int i = 0; i < tdesc->reg_defs.size (); ++i)
> >>      {
> >> -      if (regcache->register_status[i] == REG_VALID)
> >> -	{
> >> -	  bin2hex (registers, buf, register_size (tdesc, i));
> >> -	  buf += register_size (tdesc, i) * 2;
> >> -	}
> >> -      else
> >> -	{
> >> -	  memset (buf, 'x', register_size (tdesc, i) * 2);
> >> -	  buf += register_size (tdesc, i) * 2;
> >> -	}
> >> -      registers += register_size (tdesc, i);
> >> +      collect_register_as_string (regcache, i, buf);
> >> +      buf += register_size (tdesc, i) * 2;
> >>      }
> >> -  *buf = '\0';
> >>  }
> >>
> >>  void
> >> @@ -472,8 +461,15 @@ regcache_raw_get_unsigned_by_name (struct regcache *regcache,
> >>  void
> >>  collect_register_as_string (struct regcache *regcache, int n, char *buf)
> >>  {
> >> -  bin2hex (register_data (regcache, n), buf,
> >> -	   register_size (regcache->tdesc, n));
> >> +  int reg_size = register_size (regcache->tdesc, n);
> >> +
> >> +  if (regcache->register_status[n] == REG_VALID)
> >> +    bin2hex (register_data (regcache, n), buf, reg_size);
> >> +  else
> >> +    memset (buf, 'x', reg_size * 2);
> >> +
> >> +  buf += reg_size * 2;
> >> +  *buf = '\0';
> >>  }
> 
> I don't mind this improvement, but I was wondering if using the std::string variant of
> bin2hex would
> allow further simplification of this code. You wouldn't have to handle the \0 explicitly.
> 
> I guess the slightly confusing part is that collect_register_as_string finishes the string
> with \0,
> but registers_to_string ignores it and overwrites it.
> 
> In any case, I think this is a nice improvement.
> 
> Reviewed-By:  Luis Machado  <luis.machado@arm.com>

Hi Luis,

Thanks for the comments.  Overwriting the null terminator does indeed look odd, but
using the std::string variant of bin2hex would require creating intermediary copies
of pieces of the overall string.  To avoid this increased cost, I thought we could
still prefer the lower-level approach above.  (The BUF buffer we are writing into is
in practice the client_state buffer.)

Regards
-Baris



Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928