Re: Problem with 32-bit negative return values

[Mike Mason <mmlnx@us.ibm.com>]

Frank Ch. Eigler wrote:
> Hi -
> 
> On Tue, Oct 10, 2006 at 10:34:07AM -0700, Mike Mason wrote:
>> [...]
>> I'm trying to use the return value from sock_recvmsg() to determine how 
>> many bytes are received.  It ignores negative return values (errors).
>> [...]
>> But on x86_64, the negative values are interpreted and printed as large 
>> positive values:
>> RECV 1440
>> RECV 4294967285
>> [...]
> 
> It could easily be a typing/sign-extension bug in the loc2c-related
> code.  Could you check the generated C code (-p3; look for the
> _dwarf_tvar_get function)?

Here's the suspect code generated with -p3:

      l->__tmp18 =
      ({

        if (unlikely (c->nesting+2 >= MAXNESTING)) {
          c->last_error = "MAXNESTING exceeded";
          c->last_stmt = "identifier '$return' at nettop3.stp:56:15";
        } else if (likely (! c->last_error)) {
          c->nesting ++;
          function__dwarf_tvar_get_return_8 (c);
          c->nesting --;
          if (c->last_error && ! c->last_error[0])
            c->last_error = 0;
        }
        c->locals[c->nesting+1].function__dwarf_tvar_get_return_8.__retvalue;
      });
      if (likely (! c->last_error)) {
        l->__tmp19 = 0;
        _stp_printf ("RECV %lld\n", l->__tmp18);
      }


> 
> - FChE