[PATCH v4 1/6] arm64: ftrace: adjust callsite addresses examined by stack tracer

AKASHI Takahiro
2015-10-30T05:27:13Z

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 <takahiro.akashi@linaro.org>
---
arch/arm64/include/asm/ftrace.h | 5 +++--
arch/arm64/kernel/stacktrace.c | 7 ++++---
include/linux/ftrace.h | 7 +++++++
kernel/trace/trace_stack.c | 8 +++++---
4 files changed, 19 insertions(+), 8 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 8abf1ba..2e452e8 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -68,7 +68,7 @@ static inline void print_max_stack(void)
static inline void
check_stack(unsigned long ip, unsigned long *stack)
{
- unsigned long this_size, flags; unsigned long *p, *top, *start;
+ unsigned long this_size, flags; unsigned long *p, *top, *start, addr;
static int tracer_frame;
int frame_size = ACCESS_ONCE(tracer_frame);
int i, x;
@@ -115,7 +115,8 @@ 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)
+ addr = stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET;
+ if (addr == ip)
break;
}

@@ -143,7 +144,8 @@ 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]) {
+ addr = stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET;
+ if (*p == addr) {
stack_dump_trace[x] = stack_dump_trace[i++];
this_size = stack_dump_index[x++] =
(top - p) * sizeof(unsigned long);
--
1.7.9.5