arm64: ftrace: fix a stack tracer's output under function graph tracer
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@gmail.com> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> [will: fixed minor context changes conflicting with irq stack bits] Signed-off-by: Will Deacon <will.deacon@arm.com>
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@ -28,6 +28,8 @@ struct dyn_arch_ftrace {
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extern unsigned long ftrace_graph_call;
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extern void return_to_handler(void);
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static inline unsigned long ftrace_call_adjust(unsigned long addr)
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{
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/*
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@ -22,6 +22,9 @@ struct stackframe {
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unsigned long fp;
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unsigned long sp;
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unsigned long pc;
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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unsigned int graph;
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#endif
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};
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extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
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@ -164,6 +164,9 @@ void perf_callchain_kernel(struct perf_callchain_entry *entry,
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frame.fp = regs->regs[29];
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frame.sp = regs->sp;
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frame.pc = regs->pc;
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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frame.graph = current->curr_ret_stack;
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#endif
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walk_stackframe(current, &frame, callchain_trace, entry);
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}
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@ -344,6 +344,9 @@ unsigned long get_wchan(struct task_struct *p)
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frame.fp = thread_saved_fp(p);
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frame.sp = thread_saved_sp(p);
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frame.pc = thread_saved_pc(p);
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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frame.graph = p->curr_ret_stack;
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#endif
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stack_page = (unsigned long)task_stack_page(p);
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do {
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if (frame.sp < stack_page ||
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@ -43,6 +43,9 @@ void *return_address(unsigned int level)
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frame.fp = (unsigned long)__builtin_frame_address(0);
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frame.sp = current_stack_pointer;
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frame.pc = (unsigned long)return_address; /* dummy */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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frame.graph = current->curr_ret_stack;
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#endif
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walk_stackframe(current, &frame, save_return_addr, &data);
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@ -17,6 +17,7 @@
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*/
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/ftrace.h>
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#include <linux/sched.h>
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#include <linux/stacktrace.h>
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@ -66,6 +67,19 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
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frame->fp = *(unsigned long *)(fp);
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frame->pc = *(unsigned long *)(fp + 8);
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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if (tsk && tsk->ret_stack &&
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(frame->pc == (unsigned long)return_to_handler)) {
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/*
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* This is a case where function graph tracer has
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* modified a return address (LR) in a stack frame
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* to hook a function return.
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* So replace it to an original value.
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*/
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frame->pc = tsk->ret_stack[frame->graph--].ret;
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}
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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/*
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* Check whether we are going to walk through from interrupt stack
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* to task stack.
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@ -158,6 +172,9 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
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frame.sp = current_stack_pointer;
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frame.pc = (unsigned long)save_stack_trace_tsk;
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}
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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frame.graph = tsk->curr_ret_stack;
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#endif
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walk_stackframe(tsk, &frame, save_trace, &data);
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if (trace->nr_entries < trace->max_entries)
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@ -52,6 +52,9 @@ unsigned long profile_pc(struct pt_regs *regs)
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frame.fp = regs->regs[29];
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frame.sp = regs->sp;
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frame.pc = regs->pc;
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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frame.graph = -1; /* no task info */
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#endif
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do {
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int ret = unwind_frame(NULL, &frame);
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if (ret < 0)
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@ -147,17 +147,14 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
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{
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struct stackframe frame;
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unsigned long irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
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int skip;
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pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
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if (!tsk)
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tsk = current;
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if (regs) {
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frame.fp = regs->regs[29];
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frame.sp = regs->sp;
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frame.pc = regs->pc;
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} else if (tsk == current) {
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if (tsk == current) {
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frame.fp = (unsigned long)__builtin_frame_address(0);
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frame.sp = current_stack_pointer;
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frame.pc = (unsigned long)dump_backtrace;
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@ -169,14 +166,31 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
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frame.sp = thread_saved_sp(tsk);
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frame.pc = thread_saved_pc(tsk);
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}
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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frame.graph = tsk->curr_ret_stack;
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#endif
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skip = !!regs;
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pr_emerg("Call trace:\n");
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while (1) {
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unsigned long where = frame.pc;
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unsigned long stack;
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int ret;
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dump_backtrace_entry(where);
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/* skip until specified stack frame */
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if (!skip) {
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dump_backtrace_entry(where);
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} else if (frame.fp == regs->regs[29]) {
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skip = 0;
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/*
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* Mostly, this is the case where this function is
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* called in panic/abort. As exception handler's
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* stack frame does not contain the corresponding pc
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* at which an exception has taken place, use regs->pc
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* instead.
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*/
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dump_backtrace_entry(regs->pc);
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}
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ret = unwind_frame(tsk, &frame);
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if (ret < 0)
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break;
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