xref: /openbmc/linux/arch/loongarch/kernel/ftrace.c (revision dbe3ba30)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (C) 2022 Loongson Technology Corporation Limited
4  */
5 
6 #include <linux/init.h>
7 #include <linux/ftrace.h>
8 #include <linux/syscalls.h>
9 #include <linux/uaccess.h>
10 
11 #include <asm/asm.h>
12 #include <asm/asm-offsets.h>
13 #include <asm/cacheflush.h>
14 #include <asm/inst.h>
15 #include <asm/loongarch.h>
16 #include <asm/syscall.h>
17 
18 #include <asm-generic/sections.h>
19 
20 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
21 
22 /*
23  * As `call _mcount` follows LoongArch psABI, ra-saved operation and
24  * stack operation can be found before this insn.
25  */
26 
ftrace_get_parent_ra_addr(unsigned long insn_addr,int * ra_off)27 static int ftrace_get_parent_ra_addr(unsigned long insn_addr, int *ra_off)
28 {
29 	int limit = 32;
30 	union loongarch_instruction *insn;
31 
32 	insn = (union loongarch_instruction *)insn_addr;
33 
34 	do {
35 		insn--;
36 		limit--;
37 
38 		if (is_ra_save_ins(insn))
39 			*ra_off = -((1 << 12) - insn->reg2i12_format.immediate);
40 
41 	} while (!is_stack_alloc_ins(insn) && limit);
42 
43 	if (!limit)
44 		return -EINVAL;
45 
46 	return 0;
47 }
48 
prepare_ftrace_return(unsigned long self_addr,unsigned long callsite_sp,unsigned long old)49 void prepare_ftrace_return(unsigned long self_addr,
50 		unsigned long callsite_sp, unsigned long old)
51 {
52 	int ra_off;
53 	unsigned long return_hooker = (unsigned long)&return_to_handler;
54 
55 	if (unlikely(ftrace_graph_is_dead()))
56 		return;
57 
58 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
59 		return;
60 
61 	if (ftrace_get_parent_ra_addr(self_addr, &ra_off))
62 		goto out;
63 
64 	if (!function_graph_enter(old, self_addr, 0, NULL))
65 		*(unsigned long *)(callsite_sp + ra_off) = return_hooker;
66 
67 	return;
68 
69 out:
70 	ftrace_graph_stop();
71 	WARN_ON(1);
72 }
73 #endif	/* CONFIG_FUNCTION_GRAPH_TRACER */
74