dump_stack 实现分析

1 .lib/dump_stack.c

static void __dump_stack(void)
{
	dump_stack_print_info(KERN_DEFAULT);
	show_stack(NULL, NULL);
}

2 .arch/arm64/kernel/traps.c

void show_stack(struct task_struct *tsk, unsigned long *sp)
{
	dump_backtrace(NULL, tsk);
	barrier();
}

dump_backtrace 的定义如下

static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
	struct stackframe frame;
	unsigned long irq_stack_ptr;
	int skip;

	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

	if (!tsk)
		tsk = current;

	/*
	 * Switching between stacks is valid when tracing current and in
	 * non-preemptible context.
	 */
	if (tsk == current && !preemptible())
		irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
	else
		irq_stack_ptr = 0;

	if (tsk == current) {
		frame.fp = (unsigned long)__builtin_frame_address(0);
		frame.sp = current_stack_pointer;
		frame.pc = (unsigned long)dump_backtrace;
	} else {
		/*
		 * task blocked in __switch_to
		 */
		frame.fp = thread_saved_fp(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;
	printk("Call trace:\n");
	while (1) {
		unsigned long where = frame.pc;
		unsigned long stack;
		int ret;

		/* 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;
		stack = frame.sp;
		if (in_exception_text(where)) {
			/*
			 * If we switched to the irq_stack before calling this
			 * exception handler, then the pt_regs will be on the
			 * task stack. The easiest way to tell is if the large
			 * pt_regs would overlap with the end of the irq_stack.
			 */
			if (stack < irq_stack_ptr &&
			    (stack + sizeof(struct pt_regs)) > irq_stack_ptr)
				stack = IRQ_STACK_TO_TASK_STACK(irq_stack_ptr);

			dump_mem("", "Exception stack", stack,
				 stack + sizeof(struct pt_regs));
		}
	}
}

由入参可知 struct pt_regs *regs 为NULL （PS: 当出现其他异常处理时，如Panic会通过此寄存器dump backtrace） ， 所以上面的代码可以简化如下

	frame.fp = (unsigned long)__builtin_frame_address(0);
	frame.sp = current_stack_pointer;
	frame.pc = (unsigned long)dump_backtrace;/*从 dump_backtrace 这个函数开始打印*/
	skip = !!regs; /*skip 为0*/
	printk("Call trace:\n");
	while (1) {
		unsigned long where = frame.pc;
		unsigned long stack;
		int ret;

		/* skip until specified stack frame */
		if (!skip) {
			dump_backtrace_entry(where);
		} 
		ret = unwind_frame(tsk, &frame);
		if (ret < 0)
			break;
		stack = frame.sp;

上面通过 unwind_frame(tsk, &frame); 遍历帧，通过 dump_backtrace_entry(where);将pc指针打印出即打印函数。
可以参考如下 https://juejin.cn/post/6844903616524845063 了结栈帧