[PATCH v7 3/6] arm64: ftrace: fix a stack tracer's output under function graph tracer
AKASHI Takahiro
takahiro.akashi at linaro.org
Tue Dec 15 00:33:41 PST 2015
Function graph tracer modifies a return address (LR) in a stack frame
to hook a function return. This will result in many useless entries
(return_to_handler) showing up in
a) a stack tracer's output
b) perf call graph (with perf record -g)
c) dump_backtrace (at panic et al.)
For example, in case of a),
$ echo function_graph > /sys/kernel/debug/tracing/current_tracer
$ echo 1 > /proc/sys/kernel/stack_trace_enabled
$ cat /sys/kernel/debug/tracing/stack_trace
Depth Size Location (54 entries)
----- ---- --------
0) 4504 16 gic_raise_softirq+0x28/0x150
1) 4488 80 smp_cross_call+0x38/0xb8
2) 4408 48 return_to_handler+0x0/0x40
3) 4360 32 return_to_handler+0x0/0x40
...
In case of b),
$ echo function_graph > /sys/kernel/debug/tracing/current_tracer
$ perf record -e mem:XXX:x -ag -- sleep 10
$ perf report
...
| | |--0.22%-- 0x550f8
| | | 0x10888
| | | el0_svc_naked
| | | sys_openat
| | | return_to_handler
| | | return_to_handler
...
In case of c),
$ echo function_graph > /sys/kernel/debug/tracing/current_tracer
$ echo c > /proc/sysrq-trigger
...
Call trace:
[<ffffffc00044d3ac>] sysrq_handle_crash+0x24/0x30
[<ffffffc000092250>] return_to_handler+0x0/0x40
[<ffffffc000092250>] return_to_handler+0x0/0x40
...
This patch replaces such entries with real addresses preserved in
current->ret_stack[] at unwind_frame(). This way, we can cover all
the cases.
Reviewed-by: Jungseok Lee <jungseoklee85 at gmail.com>
Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
---
arch/arm64/include/asm/ftrace.h | 2 ++
arch/arm64/include/asm/stacktrace.h | 3 +++
arch/arm64/kernel/perf_callchain.c | 3 +++
arch/arm64/kernel/process.c | 3 +++
arch/arm64/kernel/return_address.c | 3 +++
arch/arm64/kernel/stacktrace.c | 17 +++++++++++++++++
arch/arm64/kernel/time.c | 3 +++
arch/arm64/kernel/traps.c | 26 ++++++++++++++++++++------
8 files changed, 54 insertions(+), 6 deletions(-)
diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index c5534fa..3c60f37 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -28,6 +28,8 @@ struct dyn_arch_ftrace {
extern unsigned long ftrace_graph_call;
+extern void return_to_handler(void);
+
static inline unsigned long ftrace_call_adjust(unsigned long addr)
{
/*
diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 6fb61c5..801a16db 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -22,6 +22,9 @@ struct stackframe {
unsigned long fp;
unsigned long sp;
unsigned long pc;
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ unsigned int graph;
+#endif
};
extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 797220d..ff46654 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -164,6 +164,9 @@ void perf_callchain_kernel(struct perf_callchain_entry *entry,
frame.fp = regs->regs[29];
frame.sp = regs->sp;
frame.pc = regs->pc;
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ frame.graph = current->curr_ret_stack;
+#endif
walk_stackframe(current, &frame, callchain_trace, entry);
}
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 98bf546..88d742b 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -344,6 +344,9 @@ unsigned long get_wchan(struct task_struct *p)
frame.fp = thread_saved_fp(p);
frame.sp = thread_saved_sp(p);
frame.pc = thread_saved_pc(p);
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ frame.graph = p->curr_ret_stack;
+#endif
stack_page = (unsigned long)task_stack_page(p);
do {
if (frame.sp < stack_page ||
diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c
index 07b37ac..1718706 100644
--- a/arch/arm64/kernel/return_address.c
+++ b/arch/arm64/kernel/return_address.c
@@ -43,6 +43,9 @@ void *return_address(unsigned int level)
frame.fp = (unsigned long)__builtin_frame_address(0);
frame.sp = current_stack_pointer;
frame.pc = (unsigned long)return_address; /* dummy */
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ frame.graph = current->curr_ret_stack;
+#endif
walk_stackframe(current, &frame, save_return_addr, &data);
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 9c7acf8..0a39049 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -17,6 +17,7 @@
*/
#include <linux/kernel.h>
#include <linux/export.h>
+#include <linux/ftrace.h>
#include <linux/sched.h>
#include <linux/stacktrace.h>
@@ -66,6 +67,19 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
frame->fp = *(unsigned long *)(fp);
frame->pc = *(unsigned long *)(fp + 8);
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ if (tsk && tsk->ret_stack &&
+ (frame->pc == (unsigned long)return_to_handler)) {
+ /*
+ * This is a case where function graph tracer has
+ * modified a return address (LR) in a stack frame
+ * to hook a function return.
+ * So replace it to an original value.
+ */
+ frame->pc = tsk->ret_stack[frame->graph--].ret;
+ }
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
/*
* Check whether we are going to walk through from interrupt stack
* to task stack.
@@ -137,6 +151,9 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
frame.sp = current_stack_pointer;
frame.pc = (unsigned long)save_stack_trace_tsk;
}
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ frame.graph = tsk->curr_ret_stack;
+#endif
walk_stackframe(tsk, &frame, save_trace, &data);
if (trace->nr_entries < trace->max_entries)
diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c
index 6e5c521..5977969 100644
--- a/arch/arm64/kernel/time.c
+++ b/arch/arm64/kernel/time.c
@@ -52,6 +52,9 @@ unsigned long profile_pc(struct pt_regs *regs)
frame.fp = regs->regs[29];
frame.sp = regs->sp;
frame.pc = regs->pc;
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ frame.graph = -1; /* no task info */
+#endif
do {
int ret = unwind_frame(NULL, &frame);
if (ret < 0)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index da45224..f140029 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -147,17 +147,14 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
struct stackframe frame;
unsigned long _irq_stack_ptr = per_cpu(irq_stack_ptr, smp_processor_id());
+ int skip;
pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
if (!tsk)
tsk = current;
- if (regs) {
- frame.fp = regs->regs[29];
- frame.sp = regs->sp;
- frame.pc = regs->pc;
- } else if (tsk == current) {
+ if (tsk == current) {
frame.fp = (unsigned long)__builtin_frame_address(0);
frame.sp = current_stack_pointer;
frame.pc = (unsigned long)dump_backtrace;
@@ -169,14 +166,31 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
frame.sp = thread_saved_sp(tsk);
frame.pc = thread_saved_pc(tsk);
}
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ frame.graph = tsk->curr_ret_stack;
+#endif
+ skip = (regs ? 1 : 0);
pr_emerg("Call trace:\n");
while (1) {
unsigned long where = frame.pc;
unsigned long stack;
int ret;
- dump_backtrace_entry(where);
+ /* skip until specified stack frame */
+ if (!skip)
+ dump_backtrace_entry(where);
+ else if (frame.fp == regs->regs[29]) {
+ skip = 0;
+ /*
+ * Mostly, this is the case where this function is
+ * called in panic/abort. As exception handler's
+ * stack frame does not contain the corresponding pc
+ * at which an exception has taken place, use regs->pc
+ * instead.
+ */
+ dump_backtrace_entry(regs->pc);
+ }
ret = unwind_frame(tsk, &frame);
if (ret < 0)
break;
--
1.7.9.5
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