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 	if (kstack_end((void *)frame->fp))
16 		return -EPERM;
17 	if (frame->fp & 0x3 || frame->fp < TASK_SIZE)
18 		return -EPERM;
19 
20 	*frame = *(struct stackframe *)frame->fp;
21 	if (__kernel_text_address(frame->lr)) {
22 		int graph = 0;
23 
24 		frame->lr = ftrace_graph_ret_addr(NULL, &graph, frame->lr,
25 				NULL);
26 	}
27 	return 0;
28 }
29 
30 static void notrace walk_stackframe(struct stackframe *fr,
31 			struct perf_callchain_entry_ctx *entry)
32 {
33 	do {
34 		perf_callchain_store(entry, fr->lr);
35 	} while (unwind_frame_kernel(fr) >= 0);
36 }
37 
38 /*
39  * Get the return address for a single stackframe and return a pointer to the
40  * next frame tail.
41  */
42 static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
43 			unsigned long fp, unsigned long reg_lr)
44 {
45 	struct stackframe buftail;
46 	unsigned long lr = 0;
47 	unsigned long *user_frame_tail = (unsigned long *)fp;
48 
49 	/* Check accessibility of one struct frame_tail beyond */
50 	if (!access_ok(user_frame_tail, sizeof(buftail)))
51 		return 0;
52 	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
53 				      sizeof(buftail)))
54 		return 0;
55 
56 	if (reg_lr != 0)
57 		lr = reg_lr;
58 	else
59 		lr = buftail.lr;
60 
61 	fp = buftail.fp;
62 	perf_callchain_store(entry, lr);
63 
64 	return fp;
65 }
66 
67 /*
68  * This will be called when the target is in user mode
69  * This function will only be called when we use
70  * "PERF_SAMPLE_CALLCHAIN" in
71  * kernel/events/core.c:perf_prepare_sample()
72  *
73  * How to trigger perf_callchain_[user/kernel] :
74  * $ perf record -e cpu-clock --call-graph fp ./program
75  * $ perf report --call-graph
76  *
77  * On C-SKY platform, the program being sampled and the C library
78  * need to be compiled with * -mbacktrace, otherwise the user
79  * stack will not contain function frame.
80  */
81 void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
82 			 struct pt_regs *regs)
83 {
84 	unsigned long fp = 0;
85 
86 	/* C-SKY does not support virtualization. */
87 	if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
88 		return;
89 
90 	fp = regs->regs[4];
91 	perf_callchain_store(entry, regs->pc);
92 
93 	/*
94 	 * While backtrace from leaf function, lr is normally
95 	 * not saved inside frame on C-SKY, so get lr from pt_regs
96 	 * at the sample point. However, lr value can be incorrect if
97 	 * lr is used as temp register
98 	 */
99 	fp = user_backtrace(entry, fp, regs->lr);
100 
101 	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
102 		fp = user_backtrace(entry, fp, 0);
103 }
104 
105 void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
106 			   struct pt_regs *regs)
107 {
108 	struct stackframe fr;
109 
110 	/* C-SKY does not support virtualization. */
111 	if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
112 		pr_warn("C-SKY does not support perf in guest mode!");
113 		return;
114 	}
115 
116 	fr.fp = regs->regs[4];
117 	fr.lr = regs->lr;
118 	walk_stackframe(&fr, entry);
119 }
120