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}
115