On arm64, no PC values returned by save_stack_trace() will match to LR
values saved in stack frames on a stack after the following commit:
   commit e306dfd06fcb ("ARM64: unwind: Fix PC calculation")
As a result, the output from stack tracer will be messed up.

This patch introduces an arch-defined macro, FTRACE_STACK_FRAME_OFFSET,
so that check_stack() can handle this case correctly.

Signed-off-by: AKASHI Takahiro <redacted>
---
arch/arm64/include/asm/ftrace.h |    5 +++--
arch/arm64/kernel/stacktrace.c  |    7 ++++---
include/linux/ftrace.h          |    7 +++++++
kernel/trace/trace_stack.c      |    5 +++--
4 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index c5534fa..2b43e20 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h

@@ -13,8 +13,9 @@

#include <asm/insn.h>

-#define MCOUNT_ADDR		((unsigned long)_mcount)
-#define MCOUNT_INSN_SIZE	AARCH64_INSN_SIZE
+#define MCOUNT_ADDR			((unsigned long)_mcount)
+#define MCOUNT_INSN_SIZE		AARCH64_INSN_SIZE
+#define FTRACE_STACK_FRAME_OFFSET	AARCH64_INSN_SIZE

#ifndef __ASSEMBLY__
#include <linux/compat.h>

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 407991b..bc0689a 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c

@@ -20,6 +20,7 @@

#include <linux/sched.h>
#include <linux/stacktrace.h>

+#include <asm/insn.h>
#include <asm/stacktrace.h>

/*

@@ -49,10 +50,10 @@ int notrace unwind_frame(struct stackframe *frame)

	frame->sp = fp + 0x10;
	frame->fp = *(unsigned long *)(fp);
	/*
-	 * -4 here because we care about the PC at time of bl,
-	 * not where the return will go.
+	 * decrement PC by AARCH64_INSN_SIZE here because we care about
+	 * the PC at time of bl, not where the return will go.
	 */
-	frame->pc = *(unsigned long *)(fp + 8) - 4;
+	frame->pc = *(unsigned long *)(fp + 8) - AARCH64_INSN_SIZE;

	return 0;
}

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 6cd8c0e..d77b195 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h

@@ -263,6 +263,13 @@ static inline void ftrace_kill(void) { }

#endif /* CONFIG_FUNCTION_TRACER */

#ifdef CONFIG_STACK_TRACER
+/*
+ * the offset value to add to return address from save_stack_trace()
+ */
+#ifndef FTRACE_STACK_FRAME_OFFSET
+#define FTRACE_STACK_FRAME_OFFSET 0
+#endif
+
extern int stack_tracer_enabled;
int
stack_trace_sysctl(struct ctl_table *table, int write,

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index b746399..30521ea 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c

@@ -105,7 +105,7 @@ check_stack(unsigned long ip, unsigned long *stack)

	/* Skip over the overhead of the stack tracer itself */
	for (i = 0; i < max_stack_trace.nr_entries; i++) {
-		if (stack_dump_trace[i] == ip)
+		if ((stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET) == ip)
			break;
	}

@@ -133,7 +133,8 @@ check_stack(unsigned long ip, unsigned long *stack)

		for (; p < top && i < max_stack_trace.nr_entries; p++) {
			if (stack_dump_trace[i] == ULONG_MAX)
				break;
-			if (*p == stack_dump_trace[i]) {
+			if (*p == (stack_dump_trace[i]
+					+ FTRACE_STACK_FRAME_OFFSET)) {
				stack_dump_trace[x] = stack_dump_trace[i++];
				this_size = stack_dump_index[x++] =
					(top - p) * sizeof(unsigned long);
--