stacktrace.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>
#include <linux/ftrace.h>
#include <linux/ptrace.h>

#ifdef CONFIG_FRAME_POINTER

struct stackframe {
	unsigned long fp;
	unsigned long ra;
};

void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
			     bool (*fn)(unsigned long, void *), void *arg)
{
	unsigned long fp, sp, pc;

	if (regs) {
		fp = frame_pointer(regs);
		sp = user_stack_pointer(regs);
		pc = instruction_pointer(regs);
	} else if (task == NULL || task == current) {
		const register unsigned long current_fp __asm__ ("r8");
		fp = current_fp;
		sp = current_stack_pointer;
		pc = (unsigned long)walk_stackframe;
	} else {
		/* task blocked in __switch_to */
		fp = thread_saved_fp(task);
		sp = thread_saved_sp(task);
		pc = thread_saved_lr(task);
	}

	for (;;) {
		unsigned long low, high;
		struct stackframe *frame;

		if (unlikely(!__kernel_text_address(pc) || fn(pc, arg)))
			break;

		/* Validate frame pointer */
		low = sp;
		high = ALIGN(sp, THREAD_SIZE);
		if (unlikely(fp < low || fp > high || fp & 0x3))
			break;
		/* Unwind stack frame */
		frame = (struct stackframe *)fp;
		sp = fp;
		fp = frame->fp;
		pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
					   (unsigned long *)(fp - 8));
	}
}

#else /* !CONFIG_FRAME_POINTER */

static void notrace walk_stackframe(struct task_struct *task,
	struct pt_regs *regs, bool (*fn)(unsigned long, void *), void *arg)
{
	unsigned long sp, pc;
	unsigned long *ksp;

	if (regs) {
		sp = user_stack_pointer(regs);
		pc = instruction_pointer(regs);
	} else if (task == NULL || task == current) {
		sp = current_stack_pointer;
		pc = (unsigned long)walk_stackframe;
	} else {
		/* task blocked in __switch_to */
		sp = thread_saved_sp(task);
		pc = thread_saved_lr(task);
	}

	if (unlikely(sp & 0x3))
		return;

	ksp = (unsigned long *)sp;
	while (!kstack_end(ksp)) {
		if (__kernel_text_address(pc) && unlikely(fn(pc, arg)))
			break;
		pc = (*ksp++) - 0x4;
	}
}
#endif /* CONFIG_FRAME_POINTER */

static bool print_trace_address(unsigned long pc, void *arg)
{
	print_ip_sym((const char *)arg, pc);
	return false;
}

void show_stack(struct task_struct *task, unsigned long *sp, const char *loglvl)
{
	pr_cont("Call Trace:\n");
	walk_stackframe(task, NULL, print_trace_address, (void *)loglvl);
}

static bool save_wchan(unsigned long pc, void *arg)
{
	if (!in_sched_functions(pc)) {
		unsigned long *p = arg;
		*p = pc;
		return true;
	}
	return false;
}

unsigned long __get_wchan(struct task_struct *task)
{
	unsigned long pc = 0;

	walk_stackframe(task, NULL, save_wchan, &pc);
	return pc;
}

#ifdef CONFIG_STACKTRACE
static bool __save_trace(unsigned long pc, void *arg, bool nosched)
{
	struct stack_trace *trace = arg;

	if (unlikely(nosched && in_sched_functions(pc)))
		return false;
	if (unlikely(trace->skip > 0)) {
		trace->skip--;
		return false;
	}

	trace->entries[trace->nr_entries++] = pc;
	return (trace->nr_entries >= trace->max_entries);
}

static bool save_trace(unsigned long pc, void *arg)
{
	return __save_trace(pc, arg, false);
}

/*
 * Save stack-backtrace addresses into a stack_trace buffer.
 */
void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
{
	walk_stackframe(tsk, NULL, save_trace, trace);
}
EXPORT_SYMBOL_GPL(save_stack_trace_tsk);

void save_stack_trace(struct stack_trace *trace)
{
	save_stack_trace_tsk(NULL, trace);
}
EXPORT_SYMBOL_GPL(save_stack_trace);

#endif /* CONFIG_STACKTRACE */