1// SPDX-License-Identifier: GPL-2.0
  2// Copyright (C) 2019 Hangzhou C-SKY Microsystems co.,ltd.
  3
  4#include <linux/perf_event.h>
  5#include <linux/uaccess.h>
  6
  7/* Kernel callchain */
  8struct stackframe {
  9	unsigned long fp;
 10	unsigned long lr;
 11};
 12
 13static int unwind_frame_kernel(struct stackframe *frame)
 14{
 15	unsigned long low = (unsigned long)task_stack_page(current);
 16	unsigned long high = low + THREAD_SIZE;
 17
 18	if (unlikely(frame->fp < low || frame->fp > high))
 19		return -EPERM;
 20
 21	if (kstack_end((void *)frame->fp) || frame->fp & 0x3)
 22		return -EPERM;
 23
 24	*frame = *(struct stackframe *)frame->fp;
 25
 26	if (__kernel_text_address(frame->lr)) {
 27		int graph = 0;
 28
 29		frame->lr = ftrace_graph_ret_addr(NULL, &graph, frame->lr,
 30				NULL);
 31	}
 32	return 0;
 33}
 34
 35static void notrace walk_stackframe(struct stackframe *fr,
 36			struct perf_callchain_entry_ctx *entry)
 37{
 38	do {
 39		perf_callchain_store(entry, fr->lr);
 40	} while (unwind_frame_kernel(fr) >= 0);
 41}
 42
 43/*
 44 * Get the return address for a single stackframe and return a pointer to the
 45 * next frame tail.
 46 */
 47static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
 48			unsigned long fp, unsigned long reg_lr)
 49{
 50	struct stackframe buftail;
 51	unsigned long lr = 0;
 52	unsigned long __user *user_frame_tail = (unsigned long __user *)fp;
 53
 54	/* Check accessibility of one struct frame_tail beyond */
 55	if (!access_ok(user_frame_tail, sizeof(buftail)))
 56		return 0;
 57	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
 58				      sizeof(buftail)))
 59		return 0;
 60
 61	if (reg_lr != 0)
 62		lr = reg_lr;
 63	else
 64		lr = buftail.lr;
 65
 66	fp = buftail.fp;
 67	perf_callchain_store(entry, lr);
 68
 69	return fp;
 70}
 71
 72/*
 73 * This will be called when the target is in user mode
 74 * This function will only be called when we use
 75 * "PERF_SAMPLE_CALLCHAIN" in
 76 * kernel/events/core.c:perf_prepare_sample()
 77 *
 78 * How to trigger perf_callchain_[user/kernel] :
 79 * $ perf record -e cpu-clock --call-graph fp ./program
 80 * $ perf report --call-graph
 81 *
 82 * On C-SKY platform, the program being sampled and the C library
 83 * need to be compiled with * -mbacktrace, otherwise the user
 84 * stack will not contain function frame.
 85 */
 86void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
 87			 struct pt_regs *regs)
 88{
 89	unsigned long fp = 0;
 90
 91	fp = regs->regs[4];
 92	perf_callchain_store(entry, regs->pc);
 93
 94	/*
 95	 * While backtrace from leaf function, lr is normally
 96	 * not saved inside frame on C-SKY, so get lr from pt_regs
 97	 * at the sample point. However, lr value can be incorrect if
 98	 * lr is used as temp register
 99	 */
100	fp = user_backtrace(entry, fp, regs->lr);
101
102	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
103		fp = user_backtrace(entry, fp, 0);
104}
105
106void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
107			   struct pt_regs *regs)
108{
109	struct stackframe fr;
110
111	fr.fp = regs->regs[4];
112	fr.lr = regs->lr;
113	walk_stackframe(&fr, entry);
114}