1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * dwarf-regs.c : Mapping of DWARF debug register numbers into register names.
4 * Extracted from probe-finder.c
5 *
6 * Written by Masami Hiramatsu <mhiramat@redhat.com>
7 */
8
9#include <stddef.h>
10#include <errno.h> /* for EINVAL */
11#include <string.h> /* for strcmp */
12#include <linux/ptrace.h> /* for struct pt_regs */
13#include <linux/kernel.h> /* for offsetof */
14#include <dwarf-regs.h>
15
16/*
17 * See arch/x86/kernel/ptrace.c.
18 * Different from it:
19 *
20 *  - Since struct pt_regs is defined differently for user and kernel,
21 *    but we want to use 'ax, bx' instead of 'rax, rbx' (which is struct
22 *    field name of user's pt_regs), we make REG_OFFSET_NAME to accept
23 *    both string name and reg field name.
24 *
25 *  - Since accessing x86_32's pt_regs from x86_64 building is difficult
26 *    and vise versa, we simply fill offset with -1, so
27 *    get_arch_regstr() still works but regs_query_register_offset()
28 *    returns error.
29 *    The only inconvenience caused by it now is that we are not allowed
30 *    to generate BPF prologue for a x86_64 kernel if perf is built for
31 *    x86_32. This is really a rare usecase.
32 *
33 *  - Order is different from kernel's ptrace.c for get_arch_regstr(). Use
34 *    the order defined by dwarf.
35 */
36
37struct pt_regs_offset {
38	const char *name;
39	int offset;
40};
41
42#define REG_OFFSET_END {.name = NULL, .offset = 0}
43
44#ifdef __x86_64__
45# define REG_OFFSET_NAME_64(n, r) {.name = n, .offset = offsetof(struct pt_regs, r)}
46# define REG_OFFSET_NAME_32(n, r) {.name = n, .offset = -1}
47#else
48# define REG_OFFSET_NAME_64(n, r) {.name = n, .offset = -1}
49# define REG_OFFSET_NAME_32(n, r) {.name = n, .offset = offsetof(struct pt_regs, r)}
50#endif
51
52/* TODO: switching by dwarf address size */
53#ifndef __x86_64__
54static const struct pt_regs_offset x86_32_regoffset_table[] = {
55	REG_OFFSET_NAME_32("%ax",	eax),
56	REG_OFFSET_NAME_32("%cx",	ecx),
57	REG_OFFSET_NAME_32("%dx",	edx),
58	REG_OFFSET_NAME_32("%bx",	ebx),
59	REG_OFFSET_NAME_32("$stack",	esp),	/* Stack address instead of %sp */
60	REG_OFFSET_NAME_32("%bp",	ebp),
61	REG_OFFSET_NAME_32("%si",	esi),
62	REG_OFFSET_NAME_32("%di",	edi),
63	REG_OFFSET_END,
64};
65
66#define regoffset_table x86_32_regoffset_table
67#else
68static const struct pt_regs_offset x86_64_regoffset_table[] = {
69	REG_OFFSET_NAME_64("%ax",	rax),
70	REG_OFFSET_NAME_64("%dx",	rdx),
71	REG_OFFSET_NAME_64("%cx",	rcx),
72	REG_OFFSET_NAME_64("%bx",	rbx),
73	REG_OFFSET_NAME_64("%si",	rsi),
74	REG_OFFSET_NAME_64("%di",	rdi),
75	REG_OFFSET_NAME_64("%bp",	rbp),
76	REG_OFFSET_NAME_64("%sp",	rsp),
77	REG_OFFSET_NAME_64("%r8",	r8),
78	REG_OFFSET_NAME_64("%r9",	r9),
79	REG_OFFSET_NAME_64("%r10",	r10),
80	REG_OFFSET_NAME_64("%r11",	r11),
81	REG_OFFSET_NAME_64("%r12",	r12),
82	REG_OFFSET_NAME_64("%r13",	r13),
83	REG_OFFSET_NAME_64("%r14",	r14),
84	REG_OFFSET_NAME_64("%r15",	r15),
85	REG_OFFSET_END,
86};
87
88#define regoffset_table x86_64_regoffset_table
89#endif
90
91/* Minus 1 for the ending REG_OFFSET_END */
92#define ARCH_MAX_REGS ((sizeof(regoffset_table) / sizeof(regoffset_table[0])) - 1)
93
94/* Return architecture dependent register string (for kprobe-tracer) */
95const char *get_arch_regstr(unsigned int n)
96{
97	return (n < ARCH_MAX_REGS) ? regoffset_table[n].name : NULL;
98}
99
100/* Reuse code from arch/x86/kernel/ptrace.c */
101/**
102 * regs_query_register_offset() - query register offset from its name
103 * @name:	the name of a register
104 *
105 * regs_query_register_offset() returns the offset of a register in struct
106 * pt_regs from its name. If the name is invalid, this returns -EINVAL;
107 */
108int regs_query_register_offset(const char *name)
109{
110	const struct pt_regs_offset *roff;
111	for (roff = regoffset_table; roff->name != NULL; roff++)
112		if (!strcmp(roff->name, name))
113			return roff->offset;
114	return -EINVAL;
115}
116