[PATCH] ppc: oops on kernel altivec assist exceptions

[Paul Mackerras <paulus@samba.org>]

If we should happen to get an altivec assist exception while executing
in the kernel, we will currently try to handle it and fail, and end up
oopsing with (apparently) a segfault.  (An altivec assist exception
occurs for floating-point altivec instructions with denormalized
inputs or outputs if the altivec unit is in java mode.)

This patch checks explicitly if we are in user mode and prints a
useful message if not.

Signed-off-by: Paul Mackerras <paulus@samba.org>

diff -urN linux-2.5/arch/ppc/kernel/traps.c pmac-2.5/arch/ppc/kernel/traps.c
--- linux-2.5/arch/ppc/kernel/traps.c	2005-03-29 16:24:53.000000000 +1000
+++ pmac-2.5/arch/ppc/kernel/traps.c	2005-03-31 08:37:53.000000000 +1000
@@ -805,6 +828,13 @@
 	if (regs->msr & MSR_VEC)
 		giveup_altivec(current);
 	preempt_enable();
+	if (!user_mode(regs)) {
+		printk(KERN_ERR "altivec assist exception in kernel mode"
+		       " at %lx\n", regs->nip);
+		debugger(regs);
+		die("altivec assist exception", regs, SIGFPE);
+		return;
+	}
 
 	err = emulate_altivec(regs);
 	if (err == 0) {
-
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