Re: Problem with 32-bit negative return values

[Mike Mason <mmlnx at us dot ibm dot 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