Remote protocol: undocumented return value for 'p'

[Raphael Zulliger <zulliger@indel.ch>]

Hi

During the development of a GDB stub, I encountered a "hidden feature": 
the 'p n' command (reading the value of a register) accepts an 
undocumented return value, which is not mentioned in the official GDB 
documentation: 'x'. the source code looks like this:

   /* If this register is unfetchable, tell the regcache.  */
   if (buf[0] == 'x')
     {
       regcache_raw_supply (regcache, reg->regnum, NULL);
       return 1;
     }


At some point during the development of my stub it was important for me 
to have this 'hidden feature'. Unfortunately, I can't remember why it 
was important - and now it seems that I don't rely on that anymore... 
However, at that time, it would have helped me to save some time if I 
could just read it from the PDF instead of searching it in the code.

The final question is: Is this feature missing in the documentation by 
'intention' or by 'mistake'? If it's the latter case, I would suggest 
adding it. Let me know if I should create an according patch.

Raphael