1 /* Definitions for Dwarf2 EH unwind support for Windows32 targets
2 Copyright (C) 2007-2023 Free Software Foundation, Inc.
3 Contributed by Pascal Obry <obry@adacore.com>
4
5 This file is part of GCC.
6
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 3, or (at your option) any later
10 version.
11
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 for more details.
16
17 Under Section 7 of GPL version 3, you are granted additional
18 permissions described in the GCC Runtime Library Exception, version
19 3.1, as published by the Free Software Foundation.
20
21 You should have received a copy of the GNU General Public License and
22 a copy of the GCC Runtime Library Exception along with this program;
23 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 <http://www.gnu.org/licenses/>. */
25
26
27 /* This file implements the md_fallback_frame_state_for routine for
28 Windows, triggered when the GCC table based unwinding process hits a
29 frame for which no unwind info has been registered. This typically
30 occurs when raising an exception from a signal handler, because the
31 handler is actually called from the OS kernel.
32
33 The basic idea is to detect that we are indeed trying to unwind past a
34 signal handler and to fill out the GCC internal unwinding structures for
35 the OS kernel frame as if it had been directly called from the
36 interrupted context.
37
38 This is all assuming that the code to set the handler asked the kernel
39 to pass a pointer to such context information.
40
41 There is three main parts.
42
43 1) The first thing to do is to check if we are in a signal context. If
44 not we can just return as there is nothing to do. We are probably on
45 some foreign code for which no unwind frame can be found. If this is
46 a call from the Windows signal handler, then:
47
48 2) We must get the signal context information.
49
50 * With the standard exception filter:
51
52 This is on Windows pointed to by an EXCEPTION_POINTERS. We know that
53 the signal handle will call an UnhandledExceptionFilter with this
54 parameter. The spec for this routine is:
55
56 LONG WINAPI UnhandledExceptionFilter(struct _EXCEPTION_POINTERS*);
57
58 So the pointer to struct _EXCEPTION_POINTERS must be somewhere on the
59 stack.
60
61 This was found experimentally to always be at offset 0 of the context
62 frame in all cases handled by this implementation.
63
64 * With the SEH exception handler:
65
66 In this case the signal context is directly on the stack as the SEH
67 exception handler has the following prototype:
68
69 DWORD
70 SEH_error_handler (PEXCEPTION_RECORD ExceptionRecord,
71 PVOID EstablisherFrame,
72 PCONTEXT ContextRecord,
73 PVOID DispatcherContext)
74
75 This was found experimentally to always be at offset 56 of the
76 context frame in all cases handled by this implementation.
77
78 3) When we have the signal context we just have to save some registers
79 and set the return address based on the program counter (Eip).
80
81 Note that this implementation follows closely the same principles as the
82 GNU/Linux and OSF ones. */
83
84 #ifndef __MINGW64__
85
86 #define WIN32_MEAN_AND_LEAN
87 #include <windows.h>
88 /* Patterns found experimentally to be on a Windows signal handler */
89
90 /* In a standard exception filter */
91
92 #define SIG_PAT1 \
93 (pc_[-2] == 0xff && pc_[-1] == 0xd0 /* call %eax */ \
94 && pc_[0] == 0x83 && pc_[1] == 0xf8) /* cmp 0xdepl,%eax */
95
96 #define SIG_PAT2 \
97 (pc_[-5] == 0xe8 && pc_[-4] == 0x68 /* call (depl16) */ \
98 && pc_[0] == 0xc3) /* ret */
99
100 /* In a Win32 SEH handler */
101
102 #define SIG_SEH1 \
103 (pc_[-5] == 0xe8 /* call addr */ \
104 && pc_[0] == 0x83 && pc_[1] == 0xc4 /* add 0xval,%esp */ \
105 && pc_[3] == 0xb8) /* mov 0xval,%eax */
106
107 #define SIG_SEH2 \
108 (pc_[-5] == 0x8b && pc_[-4] == 0x4d /* mov depl(%ebp),%ecx */ \
109 && pc_[0] == 0x64 && pc_[1] == 0x8b) /* mov %fs:(0),<reg> */ \
110
111 /* In the GCC alloca (stack probing) */
112
113 #define SIG_ALLOCA \
114 (pc_[-1] == 0x83 /* orl $0x0,(%ecx) */ \
115 && pc_[0] == 0x9 && pc_[1] == 0 \
116 && pc_[2] == 0x2d && pc_[3] == 0 /* subl $0x1000,%eax */ \
117 && pc_[4] == 0x10 && pc_[5] == 0)
118
119
120 #define MD_FALLBACK_FRAME_STATE_FOR i386_w32_fallback_frame_state
121
122 static _Unwind_Reason_Code
123 i386_w32_fallback_frame_state (struct _Unwind_Context *context,
124 _Unwind_FrameState *fs)
125
126 {
127 void * ctx_ra_ = (void *)(context->ra); /* return address */
128 void * ctx_cfa_ = (void *)(context->cfa); /* context frame address */
129 unsigned char * pc_ = (unsigned char *) ctx_ra_;
130
131 /* In the test below we look for two specific patterns found
132 experimentally to be in the Windows signal handler. */
133 if (SIG_PAT1 || SIG_PAT2 || SIG_SEH1 || SIG_SEH2)
134 {
135 PEXCEPTION_POINTERS weinfo_;
136 PCONTEXT proc_ctx_;
137 long new_cfa_;
138
139 if (SIG_SEH1)
140 proc_ctx_ = (PCONTEXT) (*(int*)(ctx_cfa_ + 56));
141 else if (SIG_SEH2)
142 proc_ctx_ = (PCONTEXT) (*(int*)(ctx_cfa_ + 8));
143 else
144 {
145 weinfo_ = (PEXCEPTION_POINTERS) (*(int*)ctx_cfa_);
146 proc_ctx_ = weinfo_->ContextRecord;
147 }
148
149 /* The new context frame address is the stack pointer. */
150 new_cfa_ = proc_ctx_->Esp;
151 fs->regs.cfa_how = CFA_REG_OFFSET;
152 fs->regs.cfa_reg = __builtin_dwarf_sp_column();
153 fs->regs.cfa_offset = new_cfa_ - (long) ctx_cfa_;
154
155 /* Restore registers. */
156 fs->regs.how[0] = REG_SAVED_OFFSET;
157 fs->regs.reg[0].loc.offset = (long)&proc_ctx_->Eax - new_cfa_;
158 fs->regs.how[3] = REG_SAVED_OFFSET;
159 fs->regs.reg[3].loc.offset = (long)&proc_ctx_->Ebx - new_cfa_;
160 fs->regs.how[1] = REG_SAVED_OFFSET;
161 fs->regs.reg[1].loc.offset = (long)&proc_ctx_->Ecx - new_cfa_;
162 fs->regs.how[2] = REG_SAVED_OFFSET;
163 fs->regs.reg[2].loc.offset = (long)&proc_ctx_->Edx - new_cfa_;
164 fs->regs.how[6] = REG_SAVED_OFFSET;
165 fs->regs.reg[6].loc.offset = (long)&proc_ctx_->Esi - new_cfa_;
166 fs->regs.how[7] = REG_SAVED_OFFSET;
167 fs->regs.reg[7].loc.offset = (long)&proc_ctx_->Edi - new_cfa_;
168 fs->regs.how[5] = REG_SAVED_OFFSET;
169 fs->regs.reg[5].loc.offset = (long)&proc_ctx_->Ebp - new_cfa_;
170 fs->regs.how[8] = REG_SAVED_OFFSET;
171 fs->regs.reg[8].loc.offset = (long)&proc_ctx_->Eip - new_cfa_;
172 fs->retaddr_column = 8;
173 fs->signal_frame = 1;
174
175 return _URC_NO_REASON;
176 }
177
178 /* Unwinding through _alloca, propagating from a trap triggered by
179 one of it's probes prior to the real SP adjustment. The only
180 operations of interest performed is "pushl %ecx", followed by
181 ecx clobbering. */
182 else if (SIG_ALLOCA)
183 {
184 /* Only one push between entry in _alloca and the probe trap. */
185 long new_cfa_ = (long) ctx_cfa_ + 4;
186
187 fs->regs.cfa_how = CFA_REG_OFFSET;
188 fs->regs.cfa_reg = __builtin_dwarf_sp_column();
189 fs->regs.cfa_offset = new_cfa_ - (long) ctx_cfa_;
190
191 /* The saved value of %ecx is at CFA - 4 */
192 fs->regs.how[1] = REG_SAVED_OFFSET;
193 fs->regs.reg[1].loc.offset = -4;
194
195 /* and what is stored at the CFA is the return address. */
196 fs->retaddr_column = 8;
197 fs->regs.how[8] = REG_SAVED_OFFSET;
198 fs->regs.reg[8].loc.offset = 0;
199 fs->signal_frame = 1;
200
201 return _URC_NO_REASON;
202 }
203 else
204 return _URC_END_OF_STACK;
205 }
206
207 #endif /* !__MINGW64__ */