Re: [PATCH RFA] Fix x86 floating point vs. thread problem

[Daniel Jacobowitz <drow at mvista dot com>]

On Thu, Dec 06, 2001 at 04:48:07PM -0700, Kevin Buettner wrote:
> The patch below fixes the problem reported by David Relson in
> 
>     http://sources.redhat.com/ml/gdb/2001-12/msg00001.html
> 
> An impressive test matrix regarding this bug has been provided by
> Emmanuel Blindauer at
> 
>     http://manu.agat.net/bug.html
> 
> Anyway, the problem is that GDB is computing the fpxregs version of
> the tag value incorrectly.  The fpxregs version of the tag value is
> simply a bitmask (of eight bits) which indicate which of the floating
> point registers is in use.  i387_fill_fxsave() was incorrectly
> shifting by twice the the number of bits that it should have.
> 
> 	* i387-nat.c (i387_fill_fxsave): Change type of ``val'' from char
> 	to short so that we don't memcpy() beyond the end of this buffer.
> 	Also, change shift value used in computing val to account for the
> 	fact that only eight bits are used.

Out of curiousity, can you explain what I saw when looking at this?  I
found that we never set any fp-related register, and yet when the value
of d was written to memory it was incorrect.  Was it not actually yet
written to memory, or was I just mistaken?

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