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 ra;
11};
12
13/*
14 * Get the return address for a single stackframe and return a pointer to the
15 * next frame tail.
16 */
17static 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 */
60void 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->sepc);
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
77bool fill_callchain(unsigned long pc, void *entry)
78{
79	return perf_callchain_store(entry, pc);
80}
81
82void notrace walk_stackframe(struct task_struct *task,
83	struct pt_regs *regs, bool (*fn)(unsigned long, void *), void *arg);
84void 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}