1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21 /*
22 * Copyright 2007 Sun Microsystems, Inc. All rights reserved.
23 * Use is subject to license terms.
24 */
25
26
27 /*
28 * The Sun Studio and GCC (patched for opensolaris/illumos) compilers
29 * implement a argument saving scheme on amd64 via the -Wu,save-args or
30 * options. When the option is specified, INTEGER type function arguments
31 * passed via registers will be saved on the stack immediately after %rbp, and
32 * will not be modified through out the life of the routine.
33 *
34 * +--------+
35 * %rbp --> | %rbp |
36 * +--------+
37 * -0x8(%rbp) | %rdi |
38 * +--------+
39 * -0x10(%rbp) | %rsi |
40 * +--------+
41 * -0x18(%rbp) | %rdx |
42 * +--------+
43 * -0x20(%rbp) | %rcx |
44 * +--------+
45 * -0x28(%rbp) | %r8 |
46 * +--------+
47 * -0x30(%rbp) | %r9 |
48 * +--------+
49 *
50 *
51 * For example, for the following function,
52 *
53 * void
54 * foo(int a1, int a2, int a3, int a4, int a5, int a6, int a7)
55 * {
56 * ...
57 * }
58 *
59 * Disassembled code will look something like the following:
60 *
61 * pushq %rbp
62 * movq %rsp, %rbp
63 * subq $imm8, %rsp **
64 * movq %rdi, -0x8(%rbp)
65 * movq %rsi, -0x10(%rbp)
66 * movq %rdx, -0x18(%rbp)
67 * movq %rcx, -0x20(%rbp)
68 * movq %r8, -0x28(%rbp)
69 * movq %r9, -0x30(%rbp)
70 * ...
71 * or
72 * pushq %rbp
73 * movq %rsp, %rbp
74 * subq $imm8, %rsp **
75 * movq %r9, -0x30(%rbp)
76 * movq %r8, -0x28(%rbp)
77 * movq %rcx, -0x20(%rbp)
78 * movq %rdx, -0x18(%rbp)
79 * movq %rsi, -0x10(%rbp)
80 * movq %rdi, -0x8(%rbp)
81 * ...
82 * or
83 * pushq %rbp
84 * movq %rsp, %rbp
85 * pushq %rdi
86 * pushq %rsi
87 * pushq %rdx
88 * pushq %rcx
89 * pushq %r8
90 * pushq %r9
91 *
92 * **: The space being reserved is in addition to what the current
93 * function prolog already reserves.
94 *
95 * We loop through the first SAVEARGS_INSN_SEQ_LEN bytes of the function
96 * looking for each argument saving instruction we would expect to see. We
97 * loop byte-by-byte, rather than doing anything smart about insn lengths,
98 * only deviating from this when we know we have our insn, and can skip the
99 * rest of it.
100 *
101 * If there are odd number of arguments to a function, additional space is
102 * reserved on the stack to maintain 16-byte alignment. For example,
103 *
104 * argc == 0: no argument saving.
105 * argc == 3: save 3, but space for 4 is reserved
106 * argc == 7: save 6.
107 */
108
109 #include <sys/sysmacros.h>
110 #include <sys/types.h>
111 #include <saveargs.h>
112
113 /*
114 * Size of the instruction sequence arrays. It should correspond to
115 * the maximum number of arguments passed via registers.
116 */
117 #define INSTR_ARRAY_SIZE 6
118
119 #define INSTR1(ins, off) (ins[(off)])
120 #define INSTR2(ins, off) (ins[(off)] + (ins[(off) + 1] << 8))
121 #define INSTR3(ins, off) \
122 (ins[(off)] + (ins[(off) + 1] << 8) + (ins[(off + 2)] << 16))
123 #define INSTR4(ins, off) \
124 (ins[(off)] + (ins[(off) + 1] << 8) + (ins[(off + 2)] << 16) + \
125 (ins[(off) + 3] << 24))
126
127 /*
128 * Sun Studio 10 patch implementation saves %rdi first;
129 * GCC 3.4.3 Sun branch implementation saves them in reverse order.
130 */
131 static const uint32_t save_instr[INSTR_ARRAY_SIZE] = {
132 0xf87d8948, /* movq %rdi, -0x8(%rbp) */
133 0xf0758948, /* movq %rsi, -0x10(%rbp) */
134 0xe8558948, /* movq %rdx, -0x18(%rbp) */
135 0xe04d8948, /* movq %rcx, -0x20(%rbp) */
136 0xd845894c, /* movq %r8, -0x28(%rbp) */
137 0xd04d894c /* movq %r9, -0x30(%rbp) */
138 };
139
140 static const uint16_t save_instr_push[] = {
141 0x57, /* pushq %rdi */
142 0x56, /* pushq %rsi */
143 0x52, /* pushq %rdx */
144 0x51, /* pushq %rcx */
145 0x5041, /* pushq %r8 */
146 0x5141 /* pushq %r9 */
147 };
148
149 /*
150 * If the return type of a function is a structure greater than 16 bytes in
151 * size, %rdi will contain the address to which it should be stored, and
152 * arguments will begin at %rsi. Studio will push all of the normal argument
153 * registers anyway, GCC will start pushing at %rsi, so we need a separate
154 * pattern.
155 */
156 static const uint32_t save_instr_sr[INSTR_ARRAY_SIZE-1] = {
157 0xf8758948, /* movq %rsi,-0x8(%rbp) */
158 0xf0558948, /* movq %rdx,-0x10(%rbp) */
159 0xe84d8948, /* movq %rcx,-0x18(%rbp) */
160 0xe045894c, /* movq %r8,-0x20(%rbp) */
161 0xd84d894c /* movq %r9,-0x28(%rbp) */
162 };
163
164 static const uint8_t save_fp_pushes[] = {
165 0x55, /* pushq %rbp */
166 0xcc /* int $0x3 */
167 };
168 #define NUM_FP_PUSHES (sizeof (save_fp_pushes) / sizeof (save_fp_pushes[0]))
169
170 static const uint32_t save_fp_movs[] = {
171 0x00e58948, /* movq %rsp,%rbp, encoding 1 */
172 0x00ec8b48, /* movq %rsp,%rbp, encoding 2 */
173 };
174 #define NUM_FP_MOVS (sizeof (save_fp_movs) / sizeof (save_fp_movs[0]))
175
176 static int
177 has_saved_fp(uint8_t *ins, int size)
178 {
179 int i, j;
180 uint32_t n;
181 int found_push = 0;
182
183 for (i = 0; i < size; i++) {
184 if (found_push == 0) {
185 n = INSTR1(ins, i);
186 for (j = 0; j <= NUM_FP_PUSHES; j++)
187 if (save_fp_pushes[j] == n) {
188 found_push = 1;
189 break;
190 }
191 } else {
192 n = INSTR3(ins, i);
193 for (j = 0; j <= NUM_FP_MOVS; j++)
194 if (save_fp_movs[j] == n)
195 return (1);
196 }
197 }
198
199 return (0);
200 }
201
202 int
203 saveargs_has_args(uint8_t *ins, size_t size, uint_t argc, int start_index)
204 {
205 int i, j;
206 uint32_t n;
207
208 argc = MIN((start_index + argc), INSTR_ARRAY_SIZE);
209
210 if (!has_saved_fp(ins, size))
211 return (SAVEARGS_NO_ARGS);
212
213 /*
214 * Compare against Sun Studio implementation
215 */
216 for (i = 4, j = 0; i <= size - 4; i++) {
217 n = INSTR4(ins, i);
218
219 if (n == save_instr[j]) {
220 i += 3;
221 if (++j >= argc)
222 return (start_index ? SAVEARGS_STRUCT_ARGS :
223 SAVEARGS_TRAD_ARGS);
224 }
225 }
226
227 /*
228 * Compare against GCC implementation
229 */
230 for (i = 4, j = argc - 1; i <= size - 4; i++) {
231 n = INSTR4(ins, i);
232
233 if (n == save_instr[j]) {
234 i += 3;
235 if (--j < start_index)
236 return (SAVEARGS_TRAD_ARGS);
237 }
238 }
239
240 /*
241 * Compare against GCC push-based implementation
242 */
243 for (i = 4, j = start_index; i <= size - 2; i += 1) {
244 n = (i >= (8 - start_index)) ? INSTR2(ins, i) : INSTR1(ins, i);
245
246 if (n == save_instr_push[j]) {
247 if (i >= (8 - start_index))
248 i += 1;
249 if (++j >= argc)
250 return (SAVEARGS_TRAD_ARGS);
251 }
252 }
253
254 /* Look for a GCC-style returned structure */
255 if (start_index != 0) {
256 for (i = 4, j = argc - 2; i <= size - 4; i++) {
257 n = INSTR4(ins, i);
258
259 if (n == save_instr_sr[j]) {
260 i += 3;
261 if (--j >= (argc - 1))
262 return (SAVEARGS_TRAD_ARGS);
263 }
264 }
265 }
266
267 return (SAVEARGS_NO_ARGS);
268 }