sparc64: Do not clobber %g7 in setcontext() trap.

That's the userland thread register, so we should never try to change
it like this.

Based upon glibc bug nptl/6577 and suggestions by Jakub Jelinek.
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc64/kernel/signal.c

@@ -2,7 +2,7 @@
  *  arch/sparc64/kernel/signal.c
  *
  *  Copyright (C) 1991, 1992  Linus Torvalds
- *  Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
+ *  Copyright (C) 1995, 2008 David S. Miller (davem@davemloft.net)
  *  Copyright (C) 1996 Miguel de Icaza (miguel@nuclecu.unam.mx)
  *  Copyright (C) 1997 Eddie C. Dost   (ecd@skynet.be)
  *  Copyright (C) 1997,1998 Jakub Jelinek   (jj@sunsite.mff.cuni.cz)
@@ -91,7 +91,9 @@ asmlinkage void sparc64_set_context(struct pt_regs *regs)
 	err |= __get_user(regs->u_regs[UREG_G4], (&(*grp)[MC_G4]));
 	err |= __get_user(regs->u_regs[UREG_G5], (&(*grp)[MC_G5]));
 	err |= __get_user(regs->u_regs[UREG_G6], (&(*grp)[MC_G6]));
-	err |= __get_user(regs->u_regs[UREG_G7], (&(*grp)[MC_G7]));
+
+	/* Skip %g7 as that's the thread register in userspace.  */
+
 	err |= __get_user(regs->u_regs[UREG_I0], (&(*grp)[MC_O0]));
 	err |= __get_user(regs->u_regs[UREG_I1], (&(*grp)[MC_O1]));
 	err |= __get_user(regs->u_regs[UREG_I2], (&(*grp)[MC_O2]));