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

[Kevin Buettner <kevinb at redhat dot com>]

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.

Index: i387-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/i387-nat.c,v
retrieving revision 1.7
diff -u -p -r1.7 i387-nat.c
--- i387-nat.c	2001/11/12 22:27:35	1.7
+++ i387-nat.c	2001/12/06 23:19:05
@@ -270,7 +270,7 @@ i387_fill_fxsave (char *fxsave, int regn
 	      {
 		/* Converting back is much easier.  */
 
-		unsigned char val = 0;
+		unsigned short val = 0;
 		unsigned short ftag;
 		int fpreg;
 
@@ -281,7 +281,7 @@ i387_fill_fxsave (char *fxsave, int regn
 		    int tag = (ftag >> (fpreg * 2)) & 3;
 
 		    if (tag != 3)
-		      val |= (1 << (fpreg * 2));
+		      val |= (1 << fpreg);
 		  }
 
 		memcpy (FXSAVE_ADDR (fxsave, i), &val, 2);