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1 | /* Target-dependent code for Linux running on i386's, for GDB. |
2 | Copyright (C) 2000 Free Software Foundation, Inc. | |
3 | ||
4 | This file is part of GDB. | |
5 | ||
6 | This program is free software; you can redistribute it and/or modify | |
7 | it under the terms of the GNU General Public License as published by | |
8 | the Free Software Foundation; either version 2 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | This program is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | GNU General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU General Public License | |
17 | along with this program; if not, write to the Free Software | |
18 | Foundation, Inc., 59 Temple Place - Suite 330, | |
19 | Boston, MA 02111-1307, USA. */ | |
20 | ||
21 | #include "defs.h" | |
22 | #include "gdbcore.h" | |
23 | #include "frame.h" | |
24 | #include "value.h" | |
25 | ||
26 | \f | |
27 | /* Recognizing signal handler frames. */ | |
28 | ||
29 | /* Linux has two flavors of signals. Normal signal handlers, and | |
30 | "realtime" (RT) signals. The RT signals can provide additional | |
31 | information to the signal handler if the SA_SIGINFO flag is set | |
32 | when establishing a signal handler using `sigaction'. It is not | |
33 | unlikely that future versions of Linux will support SA_SIGINFO for | |
34 | normal signals too. */ | |
35 | ||
36 | /* When the i386 Linux kernel calls a signal handler and the | |
37 | SA_RESTORER flag isn't set, the return address points to a bit of | |
38 | code on the stack. This function returns whether the PC appears to | |
39 | be within this bit of code. | |
40 | ||
41 | The instruction sequence for normal signals is | |
42 | pop %eax | |
43 | mov $0x77,%eax | |
44 | int $0x80 | |
45 | or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. | |
46 | ||
47 | Checking for the code sequence should be somewhat reliable, because | |
48 | the effect is to call the system call sigreturn. This is unlikely | |
49 | to occur anywhere other than a signal trampoline. | |
50 | ||
51 | It kind of sucks that we have to read memory from the process in | |
52 | order to identify a signal trampoline, but there doesn't seem to be | |
53 | any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to | |
54 | only call us if no function name could be identified, which should | |
55 | be the case since the code is on the stack. | |
56 | ||
57 | Detection of signal trampolines for handlers that set the | |
58 | SA_RESTORER flag is in general not possible. Unfortunately this is | |
59 | what the GNU C Library has been doing for quite some time now. | |
60 | However, as of version 2.1.2, the GNU C Library uses signal | |
61 | trampolines (named __restore and __restore_rt) that are identical | |
62 | to the ones used by the kernel. Therefore, these trampolines are | |
63 | supported too. */ | |
64 | ||
65 | #define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ | |
66 | #define LINUX_SIGTRAMP_OFFSET0 (0) | |
67 | #define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ | |
68 | #define LINUX_SIGTRAMP_OFFSET1 (1) | |
69 | #define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ | |
70 | #define LINUX_SIGTRAMP_OFFSET2 (6) | |
71 | ||
72 | static const unsigned char linux_sigtramp_code[] = | |
73 | { | |
74 | LINUX_SIGTRAMP_INSN0, /* pop %eax */ | |
75 | LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ | |
76 | LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ | |
77 | }; | |
78 | ||
79 | #define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) | |
80 | ||
81 | /* If PC is in a sigtramp routine, return the address of the start of | |
82 | the routine. Otherwise, return 0. */ | |
83 | ||
84 | static CORE_ADDR | |
85 | i386_linux_sigtramp_start (CORE_ADDR pc) | |
86 | { | |
87 | unsigned char buf[LINUX_SIGTRAMP_LEN]; | |
88 | ||
89 | /* We only recognize a signal trampoline if PC is at the start of | |
90 | one of the three instructions. We optimize for finding the PC at | |
91 | the start, as will be the case when the trampoline is not the | |
92 | first frame on the stack. We assume that in the case where the | |
93 | PC is not at the start of the instruction sequence, there will be | |
94 | a few trailing readable bytes on the stack. */ | |
95 | ||
96 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) | |
97 | return 0; | |
98 | ||
99 | if (buf[0] != LINUX_SIGTRAMP_INSN0) | |
100 | { | |
101 | int adjust; | |
102 | ||
103 | switch (buf[0]) | |
104 | { | |
105 | case LINUX_SIGTRAMP_INSN1: | |
106 | adjust = LINUX_SIGTRAMP_OFFSET1; | |
107 | break; | |
108 | case LINUX_SIGTRAMP_INSN2: | |
109 | adjust = LINUX_SIGTRAMP_OFFSET2; | |
110 | break; | |
111 | default: | |
112 | return 0; | |
113 | } | |
114 | ||
115 | pc -= adjust; | |
116 | ||
117 | if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) | |
118 | return 0; | |
119 | } | |
120 | ||
121 | if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) | |
122 | return 0; | |
123 | ||
124 | return pc; | |
125 | } | |
126 | ||
127 | /* This function does the same for RT signals. Here the instruction | |
128 | sequence is | |
129 | mov $0xad,%eax | |
130 | int $0x80 | |
131 | or 0xb8 0xad 0x00 0x00 0x00 0xcd 0x80. | |
132 | ||
133 | The effect is to call the system call rt_sigreturn. */ | |
134 | ||
135 | #define LINUX_RT_SIGTRAMP_INSN0 (0xb8) /* mov $NNNN,%eax */ | |
136 | #define LINUX_RT_SIGTRAMP_OFFSET0 (0) | |
137 | #define LINUX_RT_SIGTRAMP_INSN1 (0xcd) /* int */ | |
138 | #define LINUX_RT_SIGTRAMP_OFFSET1 (5) | |
139 | ||
140 | static const unsigned char linux_rt_sigtramp_code[] = | |
141 | { | |
142 | LINUX_RT_SIGTRAMP_INSN0, 0xad, 0x00, 0x00, 0x00, /* mov $0xad,%eax */ | |
143 | LINUX_RT_SIGTRAMP_INSN1, 0x80 /* int $0x80 */ | |
144 | }; | |
145 | ||
146 | #define LINUX_RT_SIGTRAMP_LEN (sizeof linux_rt_sigtramp_code) | |
147 | ||
148 | /* If PC is in a RT sigtramp routine, return the address of the start | |
149 | of the routine. Otherwise, return 0. */ | |
150 | ||
151 | static CORE_ADDR | |
152 | i386_linux_rt_sigtramp_start (CORE_ADDR pc) | |
153 | { | |
154 | unsigned char buf[LINUX_RT_SIGTRAMP_LEN]; | |
155 | ||
156 | /* We only recognize a signal trampoline if PC is at the start of | |
157 | one of the two instructions. We optimize for finding the PC at | |
158 | the start, as will be the case when the trampoline is not the | |
159 | first frame on the stack. We assume that in the case where the | |
160 | PC is not at the start of the instruction sequence, there will be | |
161 | a few trailing readable bytes on the stack. */ | |
162 | ||
163 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) | |
164 | return 0; | |
165 | ||
166 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN0) | |
167 | { | |
168 | if (buf[0] != LINUX_RT_SIGTRAMP_INSN1) | |
169 | return 0; | |
170 | ||
171 | pc -= LINUX_RT_SIGTRAMP_OFFSET1; | |
172 | ||
173 | if (read_memory_nobpt (pc, (char *) buf, LINUX_RT_SIGTRAMP_LEN) != 0) | |
174 | return 0; | |
175 | } | |
176 | ||
177 | if (memcmp (buf, linux_rt_sigtramp_code, LINUX_RT_SIGTRAMP_LEN) != 0) | |
178 | return 0; | |
179 | ||
180 | return pc; | |
181 | } | |
182 | ||
183 | /* Return whether PC is in a Linux sigtramp routine. */ | |
184 | ||
185 | int | |
186 | i386_linux_in_sigtramp (CORE_ADDR pc, char *name) | |
187 | { | |
188 | if (name) | |
189 | return STREQ ("__restore", name) || STREQ ("__restore_rt", name); | |
190 | ||
191 | return (i386_linux_sigtramp_start (pc) != 0 | |
192 | || i386_linux_rt_sigtramp_start (pc) != 0); | |
193 | } | |
194 | ||
195 | /* Assuming FRAME is for a Linux sigtramp routine, return the address | |
196 | of the associated sigcontext structure. */ | |
197 | ||
198 | CORE_ADDR | |
199 | i386_linux_sigcontext_addr (struct frame_info *frame) | |
200 | { | |
201 | CORE_ADDR pc; | |
202 | ||
203 | pc = i386_linux_sigtramp_start (frame->pc); | |
204 | if (pc) | |
205 | { | |
206 | CORE_ADDR sp; | |
207 | ||
208 | if (frame->next) | |
209 | /* If this isn't the top frame, the next frame must be for the | |
210 | signal handler itself. The sigcontext structure lives on | |
211 | the stack, right after the signum argument. */ | |
212 | return frame->next->frame + 12; | |
213 | ||
214 | /* This is the top frame. We'll have to find the address of the | |
215 | sigcontext structure by looking at the stack pointer. Keep | |
216 | in mind that the first instruction of the sigtramp code is | |
217 | "pop %eax". If the PC is at this instruction, adjust the | |
218 | returned value accordingly. */ | |
219 | sp = read_register (SP_REGNUM); | |
220 | if (pc == frame->pc) | |
221 | return sp + 4; | |
222 | return sp; | |
223 | } | |
224 | ||
225 | pc = i386_linux_rt_sigtramp_start (frame->pc); | |
226 | if (pc) | |
227 | { | |
228 | if (frame->next) | |
229 | /* If this isn't the top frame, the next frame must be for the | |
230 | signal handler itself. The sigcontext structure is part of | |
231 | the user context. A pointer to the user context is passed | |
232 | as the third argument to the signal handler. */ | |
233 | return read_memory_integer (frame->next->frame + 16, 4) + 20; | |
234 | ||
235 | /* This is the top frame. Again, use the stack pointer to find | |
236 | the address of the sigcontext structure. */ | |
237 | return read_memory_integer (read_register (SP_REGNUM) + 8, 4) + 20; | |
238 | } | |
239 | ||
240 | error ("Couldn't recognize signal trampoline."); | |
241 | return 0; | |
242 | } | |
243 | ||
244 | /* Offset to saved PC in sigcontext, from <asm/sigcontext.h>. */ | |
245 | #define LINUX_SIGCONTEXT_PC_OFFSET (56) | |
246 | ||
247 | /* Assuming FRAME is for a Linux sigtramp routine, return the saved | |
248 | program counter. */ | |
249 | ||
250 | CORE_ADDR | |
251 | i386_linux_sigtramp_saved_pc (struct frame_info *frame) | |
252 | { | |
253 | CORE_ADDR addr; | |
254 | addr = i386_linux_sigcontext_addr (frame); | |
255 | return read_memory_integer (addr + LINUX_SIGCONTEXT_PC_OFFSET, 4); | |
256 | } | |
257 | ||
258 | /* Offset to saved SP in sigcontext, from <asm/sigcontext.h>. */ | |
259 | #define LINUX_SIGCONTEXT_SP_OFFSET (28) | |
260 | ||
261 | /* Assuming FRAME is for a Linux sigtramp routine, return the saved | |
262 | stack pointer. */ | |
263 | ||
264 | CORE_ADDR | |
265 | i386_linux_sigtramp_saved_sp (struct frame_info *frame) | |
266 | { | |
267 | CORE_ADDR addr; | |
268 | addr = i386_linux_sigcontext_addr (frame); | |
269 | return read_memory_integer (addr + LINUX_SIGCONTEXT_SP_OFFSET, 4); | |
270 | } | |
271 | ||
272 | /* Immediately after a function call, return the saved pc. */ | |
273 | ||
274 | CORE_ADDR | |
275 | i386_linux_saved_pc_after_call (struct frame_info *frame) | |
276 | { | |
277 | if (frame->signal_handler_caller) | |
278 | return i386_linux_sigtramp_saved_pc (frame); | |
279 | ||
280 | return read_memory_integer (read_register (SP_REGNUM), 4); | |
281 | } |