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 #include <asm/stacktrace.h>
8 
9 /*
10  * Get the return address for a single stackframe and return a pointer to the
11  * next frame tail.
12  */
13 static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
14 				    unsigned long fp, unsigned long reg_ra)
15 {
16 	struct stackframe buftail;
17 	unsigned long ra = 0;
18 	unsigned long *user_frame_tail =
19 			(unsigned long *)(fp - sizeof(struct stackframe));
20 
21 	/* Check accessibility of one struct frame_tail beyond */
22 	if (!access_ok(user_frame_tail, sizeof(buftail)))
23 		return 0;
24 	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
25 				      sizeof(buftail)))
26 		return 0;
27 
28 	if (reg_ra != 0)
29 		ra = reg_ra;
30 	else
31 		ra = buftail.ra;
32 
33 	fp = buftail.fp;
34 	if (ra != 0)
35 		perf_callchain_store(entry, ra);
36 	else
37 		return 0;
38 
39 	return fp;
40 }
41 
42 /*
43  * This will be called when the target is in user mode
44  * This function will only be called when we use
45  * "PERF_SAMPLE_CALLCHAIN" in
46  * kernel/events/core.c:perf_prepare_sample()
47  *
48  * How to trigger perf_callchain_[user/kernel] :
49  * $ perf record -e cpu-clock --call-graph fp ./program
50  * $ perf report --call-graph
51  *
52  * On RISC-V platform, the program being sampled and the C library
53  * need to be compiled with -fno-omit-frame-pointer, otherwise
54  * the user stack will not contain function frame.
55  */
56 void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
57 			 struct pt_regs *regs)
58 {
59 	unsigned long fp = 0;
60 
61 	fp = regs->s0;
62 	perf_callchain_store(entry, regs->epc);
63 
64 	fp = user_backtrace(entry, fp, regs->ra);
65 	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
66 		fp = user_backtrace(entry, fp, 0);
67 }
68 
69 static bool fill_callchain(void *entry, unsigned long pc)
70 {
71 	return perf_callchain_store(entry, pc);
72 }
73 
74 void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
75 			   struct pt_regs *regs)
76 {
77 	walk_stackframe(NULL, regs, fill_callchain, entry);
78 }
79