Stack checking extensions

This patch adds:

 - Normal builds are done with -fstack-protector (we want to investigate
using -fstack-protector-strong on gcc4.9 but for now we just use that

 - Build with STACK_CHECK=1 will use -fstack-protector-all and -pg and
will check the stack in mcount

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

3 files changed, 20 insertions, 1 deletions

diff --git a/asm/asm-offsets.c b/asm/asm-offsets.c
index e33c181..4fb2344 100644
--- a/asm/asm-offsets.c
+++ b/asm/asm-offsets.c
@@ -36,6 +36,10 @@ int main(void)
 	OFFSET(CPUTHREAD_SAVE_R1, cpu_thread, save_r1);
 	OFFSET(CPUTHREAD_STATE, cpu_thread, state);
 	OFFSET(CPUTHREAD_CUR_TOKEN, cpu_thread, current_token);
+	DEFINE(CPUTHREAD_GAP, sizeof(struct cpu_thread) + STACK_SAFETY_GAP);
+	OFFSET(CPUTHREAD_STACK_BOT_MARK, cpu_thread, stack_bot_mark);
+	OFFSET(CPUTHREAD_STACK_BOT_PC, cpu_thread, stack_bot_pc);
+	OFFSET(CPUTHREAD_STACK_BOT_TOK, cpu_thread, stack_bot_tok);
 
 	OFFSET(STACK_TYPE,	stack_frame, type);
 	OFFSET(STACK_LOCALS,	stack_frame, locals);
diff --git a/asm/head.S b/asm/head.S
index a56f2bb..75eb170 100644
--- a/asm/head.S
+++ b/asm/head.S
@@ -308,8 +308,14 @@ boot_entry:
 	addi	%r3,%r3,8
 	bdnz	1b
 
-	/* Jump to C */
+	/* Get our per-cpu pointer into r13 */
 	GET_CPU()
+
+	/* Initialize stack bottom mark to 0, it will be updated in C code */
+	li	%r0,0
+	std	%r0,CPUTHREAD_STACK_BOT_MARK(%r13)
+
+	/* Jump to C */
 	mr	%r3,%r27
 	mr	%r4,%r25
 	bl	main_cpu_entry
diff --git a/asm/misc.S b/asm/misc.S
index ccb30d1..00c7f78 100644
--- a/asm/misc.S
+++ b/asm/misc.S
@@ -17,6 +17,7 @@
 #include <asm-utils.h>
 #include <asm-offsets.h>
 #include <processor.h>
+#include <stack.h>
 
 	.section ".text","ax"
 	.balign	0x10
@@ -41,3 +42,11 @@ trigger_attn:
 	isync
 	attn
 	blr
+
+#ifdef STACK_CHECK_ENABLED
+.global _mcount
+_mcount:
+	mr	%r3,%r1
+	mflr	%r4
+	b	__mcount_stack_check
+#endif