1 // SPDX-License-Identifier: GPL-2.0-only
3 * Stack tracing support
5 * Copyright (C) 2012 ARM Ltd.
7 #include <linux/kernel.h>
8 #include <linux/export.h>
9 #include <linux/ftrace.h>
10 #include <linux/kprobes.h>
11 #include <linux/sched.h>
12 #include <linux/sched/debug.h>
13 #include <linux/sched/task_stack.h>
14 #include <linux/stacktrace.h>
17 #include <asm/stack_pointer.h>
18 #include <asm/stacktrace.h>
21 * AArch64 PCS assigns the frame pointer to x29.
23 * A simple function prologue looks like this:
28 * A simple function epilogue looks like this:
35 * Unwind from one frame record (A) to the next frame record (B).
37 * We terminate early if the location of B indicates a malformed chain of frame
38 * records (e.g. a cycle), determined based on the location and fp value of A
39 * and the location (but not the fp value) of B.
41 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
43 unsigned long fp = frame->fp;
44 struct stack_info info;
52 if (!on_accessible_stack(tsk, fp, &info))
55 if (test_bit(info.type, frame->stacks_done))
59 * As stacks grow downward, any valid record on the same stack must be
60 * at a strictly higher address than the prior record.
62 * Stacks can nest in several valid orders, e.g.
64 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
65 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
67 * ... but the nesting itself is strict. Once we transition from one
68 * stack to another, it's never valid to unwind back to that first
71 if (info.type == frame->prev_type) {
72 if (fp <= frame->prev_fp)
75 set_bit(frame->prev_type, frame->stacks_done);
79 * Record this frame record's values and location. The prev_fp and
80 * prev_type are only meaningful to the next unwind_frame() invocation.
82 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
83 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
85 frame->prev_type = info.type;
87 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
89 (frame->pc == (unsigned long)return_to_handler)) {
90 struct ftrace_ret_stack *ret_stack;
92 * This is a case where function graph tracer has
93 * modified a return address (LR) in a stack frame
94 * to hook a function return.
95 * So replace it to an original value.
97 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
98 if (WARN_ON_ONCE(!ret_stack))
100 frame->pc = ret_stack->ret;
102 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
105 * Frames created upon entry from EL0 have NULL FP and PC values, so
106 * don't bother reporting these. Frames created by __noreturn functions
107 * might have a valid FP even if PC is bogus, so only terminate where
110 if (!frame->fp && !frame->pc)
115 NOKPROBE_SYMBOL(unwind_frame);
117 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
118 int (*fn)(struct stackframe *, void *), void *data)
125 ret = unwind_frame(tsk, frame);
130 NOKPROBE_SYMBOL(walk_stackframe);
132 #ifdef CONFIG_STACKTRACE
133 struct stack_trace_data {
134 struct stack_trace *trace;
135 unsigned int no_sched_functions;
139 static int save_trace(struct stackframe *frame, void *d)
141 struct stack_trace_data *data = d;
142 struct stack_trace *trace = data->trace;
143 unsigned long addr = frame->pc;
145 if (data->no_sched_functions && in_sched_functions(addr))
152 trace->entries[trace->nr_entries++] = addr;
154 return trace->nr_entries >= trace->max_entries;
157 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
159 struct stack_trace_data data;
160 struct stackframe frame;
163 data.skip = trace->skip;
164 data.no_sched_functions = 0;
166 start_backtrace(&frame, regs->regs[29], regs->pc);
167 walk_stackframe(current, &frame, save_trace, &data);
169 EXPORT_SYMBOL_GPL(save_stack_trace_regs);
171 static noinline void __save_stack_trace(struct task_struct *tsk,
172 struct stack_trace *trace, unsigned int nosched)
174 struct stack_trace_data data;
175 struct stackframe frame;
177 if (!try_get_task_stack(tsk))
181 data.skip = trace->skip;
182 data.no_sched_functions = nosched;
184 if (tsk != current) {
185 start_backtrace(&frame, thread_saved_fp(tsk),
186 thread_saved_pc(tsk));
188 /* We don't want this function nor the caller */
190 start_backtrace(&frame,
191 (unsigned long)__builtin_frame_address(0),
192 (unsigned long)__save_stack_trace);
195 walk_stackframe(tsk, &frame, save_trace, &data);
199 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
201 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
203 __save_stack_trace(tsk, trace, 1);
206 void save_stack_trace(struct stack_trace *trace)
208 __save_stack_trace(current, trace, 0);
211 EXPORT_SYMBOL_GPL(save_stack_trace);