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/pointer_auth.h>
18 #include <asm/stack_pointer.h>
19 #include <asm/stacktrace.h>
22 * AArch64 PCS assigns the frame pointer to x29.
24 * A simple function prologue looks like this:
29 * A simple function epilogue looks like this:
36 void start_backtrace(struct stackframe *frame, unsigned long fp,
41 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
46 * Prime the first unwind.
48 * In unwind_frame() we'll check that the FP points to a valid stack,
49 * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
50 * treated as a transition to whichever stack that happens to be. The
51 * prev_fp value won't be used, but we set it to 0 such that it is
52 * definitely not an accessible stack address.
54 bitmap_zero(frame->stacks_done, __NR_STACK_TYPES);
56 frame->prev_type = STACK_TYPE_UNKNOWN;
60 * Unwind from one frame record (A) to the next frame record (B).
62 * We terminate early if the location of B indicates a malformed chain of frame
63 * records (e.g. a cycle), determined based on the location and fp value of A
64 * and the location (but not the fp value) of B.
66 int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
68 unsigned long fp = frame->fp;
69 struct stack_info info;
71 /* Terminal record; nothing to unwind */
81 if (!on_accessible_stack(tsk, fp, &info))
84 if (test_bit(info.type, frame->stacks_done))
88 * As stacks grow downward, any valid record on the same stack must be
89 * at a strictly higher address than the prior record.
91 * Stacks can nest in several valid orders, e.g.
93 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
94 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
96 * ... but the nesting itself is strict. Once we transition from one
97 * stack to another, it's never valid to unwind back to that first
100 if (info.type == frame->prev_type) {
101 if (fp <= frame->prev_fp)
104 set_bit(frame->prev_type, frame->stacks_done);
108 * Record this frame record's values and location. The prev_fp and
109 * prev_type are only meaningful to the next unwind_frame() invocation.
111 frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
112 frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
114 frame->prev_type = info.type;
116 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
117 if (tsk->ret_stack &&
118 (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) {
119 struct ftrace_ret_stack *ret_stack;
121 * This is a case where function graph tracer has
122 * modified a return address (LR) in a stack frame
123 * to hook a function return.
124 * So replace it to an original value.
126 ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
127 if (WARN_ON_ONCE(!ret_stack))
129 frame->pc = ret_stack->ret;
131 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
133 frame->pc = ptrauth_strip_insn_pac(frame->pc);
137 NOKPROBE_SYMBOL(unwind_frame);
139 void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
140 bool (*fn)(void *, unsigned long), void *data)
145 if (!fn(data, frame->pc))
147 ret = unwind_frame(tsk, frame);
152 NOKPROBE_SYMBOL(walk_stackframe);
154 static void dump_backtrace_entry(unsigned long where, const char *loglvl)
156 printk("%s %pS\n", loglvl, (void *)where);
159 void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
162 struct stackframe frame;
165 pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
176 if (!try_get_task_stack(tsk))
179 if (tsk == current) {
180 start_backtrace(&frame,
181 (unsigned long)__builtin_frame_address(0),
182 (unsigned long)dump_backtrace);
185 * task blocked in __switch_to
187 start_backtrace(&frame,
188 thread_saved_fp(tsk),
189 thread_saved_pc(tsk));
192 printk("%sCall trace:\n", loglvl);
194 /* skip until specified stack frame */
196 dump_backtrace_entry(frame.pc, loglvl);
197 } else if (frame.fp == regs->regs[29]) {
200 * Mostly, this is the case where this function is
201 * called in panic/abort. As exception handler's
202 * stack frame does not contain the corresponding pc
203 * at which an exception has taken place, use regs->pc
206 dump_backtrace_entry(regs->pc, loglvl);
208 } while (!unwind_frame(tsk, &frame));
213 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
215 dump_backtrace(NULL, tsk, loglvl);
219 #ifdef CONFIG_STACKTRACE
221 noinline void arch_stack_walk(stack_trace_consume_fn consume_entry,
222 void *cookie, struct task_struct *task,
223 struct pt_regs *regs)
225 struct stackframe frame;
228 start_backtrace(&frame, regs->regs[29], regs->pc);
229 else if (task == current)
230 start_backtrace(&frame,
231 (unsigned long)__builtin_frame_address(1),
232 (unsigned long)__builtin_return_address(0));
234 start_backtrace(&frame, thread_saved_fp(task),
235 thread_saved_pc(task));
237 walk_stackframe(task, &frame, consume_entry, cookie);