Re: [RFA] mips: Fix "info registers" output

[Daniel Jacobowitz <dmj+@andrew.cmu.edu>]

On Thu, Jun 21, 2001 at 09:57:18PM +0300, Eli Zaretskii wrote:
> > There was indeed a bug on that path of the code, but it doesn't
> > actually affect the output.  We have this:
> > 
> >   raw_buffer[0] = (char *) alloca (REGISTER_RAW_SIZE (FP0_REGNUM));
> >   raw_buffer[1] = (char *) alloca (REGISTER_RAW_SIZE (FP0_REGNUM));
> >   dbl_buffer = (char *) alloca (2 * REGISTER_RAW_SIZE (FP0_REGNUM));
> > 
> >   /* Get the data in raw format.  */
> >   if (read_relative_register_raw_bytes (regnum, raw_buffer[HI]))
> >     error ("can't read register %d (%s)", regnum, REGISTER_NAME (regnum));
> > 
> > [snip]
> > 
> >       memcpy (dbl_buffer, raw_buffer[HI], 2 * REGISTER_RAW_SIZE (FP0_REGNUM));
> >       flt1 = unpack_double (builtin_type_float,
> >                             &raw_buffer[HI][offset], &inv1);
> >       doub = unpack_double (builtin_type_double, dbl_buffer, &inv3);
> > 
> > So we're copying 2 * 8 bytes out of an 8 byte buffer.
> 
> I don't think so.  The memcpy part uses raw_buffer[HI] as its address,
> but the two buffers whose addresses are in raw_buffer[0] and
> raw_buffer[1] are layed out on the stack one after the other.  So you
> have enough space there, and memcpy can copy up to 2*8 bytes without
> fear.  It's nasty code, but it works.  (No, I didn't write that code ;-)

Well, there's still issues.  We only initialized one register's worth
of data, for one thing.  And we only need one register's worth.

> > The real killer is on the other branch, size == 4:
> >       memcpy (dbl_buffer, raw_buffer, 2 * REGISTER_RAW_SIZE (FP0_REGNUM));
> > 
> > raw_buffer points to 8 bytes, sure enough - but they're both pointers
> > to four byte buffers before my patch.  That won't decode.
> 
> So why replacing raw_buffer with raw_buffer[HI] in the call to memcpy
> isn't all that is needed to fix this?

HI could be 0 or 1.  It's not clear what order we want to end up with,
or when we want to byteswap.

There's slightly less invasive corrections for this, but we have the
handy REGISTER_CONVERT_TO_TYPE macro.  We use it in the code for 'info
register f0', so I made us use the same code in 'info registers'.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer