sh: initial stack protector support.

This implements basic -fstack-protector support, based on the early ARM
version in c743f38013. The SMP case is
limited to the initial canary value, while the UP case handles per-task
granularity (limited to 32-bit sh until a new enough sh64 compiler
manifests itself).

Signed-off-by: Filippo Arcidiacono <filippo.arcidiacono@st.com>
Reviewed-by: Carmelo Amoroso <carmelo.amoroso@st.com>
Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/process_32.c

@@ -22,6 +22,7 @@
 #include <linux/ftrace.h>
 #include <linux/hw_breakpoint.h>
 #include <linux/prefetch.h>
+#include <linux/stackprotector.h>
 #include <asm/uaccess.h>
 #include <asm/mmu_context.h>
 #include <asm/fpu.h>
@@ -220,6 +221,10 @@ __switch_to(struct task_struct *prev, struct task_struct *next)
 {
 	struct thread_struct *next_t = &next->thread;
 
+#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
+	__stack_chk_guard = next->stack_canary;
+#endif
+
 	unlazy_fpu(prev, task_pt_regs(prev));
 
 	/* we're going to use this soon, after a few expensive things */