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 */
13static 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 *user_frame_tail =
19		(unsigned long __user *)(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 */
56void 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
69static bool fill_callchain(void *entry, unsigned long pc)
70{
71	return perf_callchain_store(entry, pc) == 0;
72}
73
74void 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