1/*
  2 * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
  3 *
  4 * This program is free software; you can redistribute it and/or
  5 * modify it under the terms of the GNU General Public License
  6 * as published by the Free Software Foundation; either version 2
  7 * of the License, or (at your option) any later version.
  8 *
  9 * This program is distributed in the hope that it will be useful,
 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 12 * GNU General Public License for more details.
 13 *
 14 * You should have received a copy of the GNU General Public License
 15 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 16 */
 17
 18#include <stdio.h>
 19#include <stdlib.h>
 20
 21#define unlikely(cond) (cond)
 22#include "insn/insn.h"
 23#include "insn/inat.c"
 24#include "insn/insn.c"
 25
 26#include "../../elf.h"
 27#include "../../arch.h"
 28#include "../../warn.h"
 29
 30static int is_x86_64(struct elf *elf)
 31{
 32	switch (elf->ehdr.e_machine) {
 33	case EM_X86_64:
 34		return 1;
 35	case EM_386:
 36		return 0;
 37	default:
 38		WARN("unexpected ELF machine type %d", elf->ehdr.e_machine);
 39		return -1;
 40	}
 41}
 42
 43int arch_decode_instruction(struct elf *elf, struct section *sec,
 44			    unsigned long offset, unsigned int maxlen,
 45			    unsigned int *len, unsigned char *type,
 46			    unsigned long *immediate)
 47{
 48	struct insn insn;
 49	int x86_64;
 50	unsigned char op1, op2, ext;
 51
 52	x86_64 = is_x86_64(elf);
 53	if (x86_64 == -1)
 54		return -1;
 55
 56	insn_init(&insn, (void *)(sec->data + offset), maxlen, x86_64);
 57	insn_get_length(&insn);
 58	insn_get_opcode(&insn);
 59	insn_get_modrm(&insn);
 60	insn_get_immediate(&insn);
 61
 62	if (!insn_complete(&insn)) {
 63		WARN_FUNC("can't decode instruction", sec, offset);
 64		return -1;
 65	}
 66
 67	*len = insn.length;
 68	*type = INSN_OTHER;
 69
 70	if (insn.vex_prefix.nbytes)
 71		return 0;
 72
 73	op1 = insn.opcode.bytes[0];
 74	op2 = insn.opcode.bytes[1];
 75
 76	switch (op1) {
 77	case 0x55:
 78		if (!insn.rex_prefix.nbytes)
 79			/* push rbp */
 80			*type = INSN_FP_SAVE;
 81		break;
 82
 83	case 0x5d:
 84		if (!insn.rex_prefix.nbytes)
 85			/* pop rbp */
 86			*type = INSN_FP_RESTORE;
 87		break;
 88
 89	case 0x70 ... 0x7f:
 90		*type = INSN_JUMP_CONDITIONAL;
 91		break;
 92
 93	case 0x89:
 94		if (insn.rex_prefix.nbytes == 1 &&
 95		    insn.rex_prefix.bytes[0] == 0x48 &&
 96		    insn.modrm.nbytes && insn.modrm.bytes[0] == 0xe5)
 97			/* mov rsp, rbp */
 98			*type = INSN_FP_SETUP;
 99		break;
100
101	case 0x90:
102		*type = INSN_NOP;
103		break;
104
105	case 0x0f:
106		if (op2 >= 0x80 && op2 <= 0x8f)
107			*type = INSN_JUMP_CONDITIONAL;
108		else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 ||
109			 op2 == 0x35)
110			/* sysenter, sysret */
111			*type = INSN_CONTEXT_SWITCH;
112		else if (op2 == 0x0b || op2 == 0xb9)
113			/* ud2 */
114			*type = INSN_BUG;
115		else if (op2 == 0x0d || op2 == 0x1f)
116			/* nopl/nopw */
117			*type = INSN_NOP;
118		else if (op2 == 0x01 && insn.modrm.nbytes &&
119			 (insn.modrm.bytes[0] == 0xc2 ||
120			  insn.modrm.bytes[0] == 0xd8))
121			/* vmlaunch, vmrun */
122			*type = INSN_CONTEXT_SWITCH;
123
124		break;
125
126	case 0xc9: /* leave */
127		*type = INSN_FP_RESTORE;
128		break;
129
130	case 0xe3: /* jecxz/jrcxz */
131		*type = INSN_JUMP_CONDITIONAL;
132		break;
133
134	case 0xe9:
135	case 0xeb:
136		*type = INSN_JUMP_UNCONDITIONAL;
137		break;
138
139	case 0xc2:
140	case 0xc3:
141		*type = INSN_RETURN;
142		break;
143
144	case 0xc5: /* iret */
145	case 0xca: /* retf */
146	case 0xcb: /* retf */
147		*type = INSN_CONTEXT_SWITCH;
148		break;
149
150	case 0xe8:
151		*type = INSN_CALL;
152		break;
153
154	case 0xff:
155		ext = X86_MODRM_REG(insn.modrm.bytes[0]);
156		if (ext == 2 || ext == 3)
157			*type = INSN_CALL_DYNAMIC;
158		else if (ext == 4)
159			*type = INSN_JUMP_DYNAMIC;
160		else if (ext == 5) /*jmpf */
161			*type = INSN_CONTEXT_SWITCH;
162
163		break;
164
165	default:
166		break;
167	}
168
169	*immediate = insn.immediate.nbytes ? insn.immediate.value : 0;
170
171	return 0;
172}