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 ra;
11 };
12 
13 /*
14  * Get the return address for a single stackframe and return a pointer to the
15  * next frame tail.
16  */
17 static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
18 				    unsigned long fp, unsigned long reg_ra)
19 {
20 	struct stackframe buftail;
21 	unsigned long ra = 0;
22 	unsigned long *user_frame_tail =
23 			(unsigned long *)(fp - sizeof(struct stackframe));
24 
25 	/* Check accessibility of one struct frame_tail beyond */
26 	if (!access_ok(user_frame_tail, sizeof(buftail)))
27 		return 0;
28 	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
29 				      sizeof(buftail)))
30 		return 0;
31 
32 	if (reg_ra != 0)
33 		ra = reg_ra;
34 	else
35 		ra = buftail.ra;
36 
37 	fp = buftail.fp;
38 	if (ra != 0)
39 		perf_callchain_store(entry, ra);
40 	else
41 		return 0;
42 
43 	return fp;
44 }
45 
46 /*
47  * This will be called when the target is in user mode
48  * This function will only be called when we use
49  * "PERF_SAMPLE_CALLCHAIN" in
50  * kernel/events/core.c:perf_prepare_sample()
51  *
52  * How to trigger perf_callchain_[user/kernel] :
53  * $ perf record -e cpu-clock --call-graph fp ./program
54  * $ perf report --call-graph
55  *
56  * On RISC-V platform, the program being sampled and the C library
57  * need to be compiled with -fno-omit-frame-pointer, otherwise
58  * the user stack will not contain function frame.
59  */
60 void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
61 			 struct pt_regs *regs)
62 {
63 	unsigned long fp = 0;
64 
65 	/* RISC-V does not support perf in guest mode. */
66 	if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
67 		return;
68 
69 	fp = regs->s0;
70 	perf_callchain_store(entry, regs->epc);
71 
72 	fp = user_backtrace(entry, fp, regs->ra);
73 	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
74 		fp = user_backtrace(entry, fp, 0);
75 }
76 
77 bool fill_callchain(unsigned long pc, void *entry)
78 {
79 	return perf_callchain_store(entry, pc);
80 }
81 
82 void notrace walk_stackframe(struct task_struct *task,
83 	struct pt_regs *regs, bool (*fn)(unsigned long, void *), void *arg);
84 void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
85 			   struct pt_regs *regs)
86 {
87 	/* RISC-V does not support perf in guest mode. */
88 	if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
89 		pr_warn("RISC-V does not support perf in guest mode!");
90 		return;
91 	}
92 
93 	walk_stackframe(NULL, regs, fill_callchain, entry);
94 }
95