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 */
8 struct stackframe {
9 	unsigned long fp;
10 	unsigned long lr;
11 };
12 
13 static 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 
35 static 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  */
47 static 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_frame_tail = (unsigned long *)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  */
86 void 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 
106 void 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