1/* Definitions for Dwarf2 EH unwind support for Windows32 targets
2   Copyright (C) 2007-2015 Free Software Foundation, Inc.
3   Contributed by Pascal Obry  <obry@adacore.com>
4
5This file is part of GCC.
6
7GCC is free software; you can redistribute it and/or modify it under
8the terms of the GNU General Public License as published by the Free
9Software Foundation; either version 3, or (at your option) any later
10version.
11
12GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13WARRANTY; without even the implied warranty of MERCHANTABILITY or
14FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
15for more details.
16
17Under Section 7 of GPL version 3, you are granted additional
18permissions described in the GCC Runtime Library Exception, version
193.1, as published by the Free Software Foundation.
20
21You should have received a copy of the GNU General Public License and
22a copy of the GCC Runtime Library Exception along with this program;
23see 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
122static _Unwind_Reason_Code
123i386_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.reg[0].how = REG_SAVED_OFFSET;
157      fs->regs.reg[0].loc.offset = (long)&proc_ctx_->Eax - new_cfa_;
158      fs->regs.reg[3].how = REG_SAVED_OFFSET;
159      fs->regs.reg[3].loc.offset = (long)&proc_ctx_->Ebx - new_cfa_;
160      fs->regs.reg[1].how = REG_SAVED_OFFSET;
161      fs->regs.reg[1].loc.offset = (long)&proc_ctx_->Ecx - new_cfa_;
162      fs->regs.reg[2].how = REG_SAVED_OFFSET;
163      fs->regs.reg[2].loc.offset = (long)&proc_ctx_->Edx - new_cfa_;
164      fs->regs.reg[6].how = REG_SAVED_OFFSET;
165      fs->regs.reg[6].loc.offset = (long)&proc_ctx_->Esi - new_cfa_;
166      fs->regs.reg[7].how = REG_SAVED_OFFSET;
167      fs->regs.reg[7].loc.offset = (long)&proc_ctx_->Edi - new_cfa_;
168      fs->regs.reg[5].how = REG_SAVED_OFFSET;
169      fs->regs.reg[5].loc.offset = (long)&proc_ctx_->Ebp - new_cfa_;
170      fs->regs.reg[8].how = 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.reg[1].how = 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.reg[8].how = 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__ */
208