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Re: [RFA] mips: Fix "info registers" output
On Thu, Jun 21, 2001 at 07:31:15PM +0300, Eli Zaretskii wrote:
>
> On Thu, 21 Jun 2001, Daniel Jacobowitz wrote:
>
> > - the decoding of double-precision arguments was completely broken.
> > In addition to copying unallocated memory, and getting the byte order
> > wrong, we tried to decode two four-byte pointers to data instead of the
> > data itself. Thus the doubles were generally 'nan'.
> >
> > - If the number of GPRs fit precisely on an integer number of rows,
> > blank space would be printed without even a trailing newline, and the
> > prompt would be mysteriously indented.
>
> I cannot reproduce this on SGI Irix 6.5, which also uses mips-tdeps.c. I
> used a small throw-away FP program and all the FP registers printed
> perfectly okay. No NaNs at all. info registers seems also okay.
>
> Perhaps I didn't try exactly what you did. Any further hints?
Really? Hmm. I looked over the code and it seemed that both branches
were wrong; however, I could be mistaken...
Aha! Let me guess - Irix 6.5 is using the FP registers in 8 byte mode,
right? 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. But float is
still 4 bytes and double still 8 bytes, so as long as we don't clobber
the stack we shouldn't see a real problem.
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.
--
Daniel Jacobowitz Carnegie Mellon University
MontaVista Software Debian GNU/Linux Developer