libgcc/config/i386/w32-unwind.h

   1 /* Definitions for Dwarf2 EH unwind support for Windows32 targets
   2    Copyright (C) 2007, 2009, 2010, 2011
   3    Free Software Foundation, Inc.
   4    Contributed by Pascal Obry  <obry@adacore.com>
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it under
   9 the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 3, or (at your option) any later
  11 version.
  12
  13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  16 for more details.
  17
  18 Under Section 7 of GPL version 3, you are granted additional
  19 permissions described in the GCC Runtime Library Exception, version
  20 3.1, as published by the Free Software Foundation.
  21
  22 You should have received a copy of the GNU General Public License and
  23 a copy of the GCC Runtime Library Exception along with this program;
  24 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  25 <http://www.gnu.org/licenses/>.  */
  26
  27
  28 /* This file implements the md_fallback_frame_state_for routine for
  29    Windows, triggered when the GCC table based unwinding process hits a
  30    frame for which no unwind info has been registered. This typically
  31    occurs when raising an exception from a signal handler, because the
  32    handler is actually called from the OS kernel.
  33
  34    The basic idea is to detect that we are indeed trying to unwind past a
  35    signal handler and to fill out the GCC internal unwinding structures for
  36    the OS kernel frame as if it had been directly called from the
  37    interrupted context.
  38
  39    This is all assuming that the code to set the handler asked the kernel
  40    to pass a pointer to such context information.
  41
  42    There is three main parts.
  43
  44    1) The first thing to do is to check if we are in a signal context. If
  45       not we can just return as there is nothing to do. We are probably on
  46       some foreign code for which no unwind frame can be found. If this is
  47       a call from the Windows signal handler, then:
  48
  49    2) We must get the signal context information.
  50
  51       * With the standard exception filter:
  52
  53       This is on Windows pointed to by an EXCEPTION_POINTERS. We know that
  54       the signal handle will call an UnhandledExceptionFilter with this
  55       parameter. The spec for this routine is:
  56
  57          LONG WINAPI UnhandledExceptionFilter(struct _EXCEPTION_POINTERS*);
  58
  59       So the pointer to struct _EXCEPTION_POINTERS must be somewhere on the
  60       stack.
  61
  62       This was found experimentally to always be at offset 0 of the context
  63       frame in all cases handled by this implementation.
  64
  65       * With the SEH exception handler:
  66
  67       In this case the signal context is directly on the stack as the SEH
  68       exception handler has the following prototype:
  69
  70          DWORD
  71          SEH_error_handler (PEXCEPTION_RECORD ExceptionRecord,
  72                             PVOID EstablisherFrame,
  73                             PCONTEXT ContextRecord,
  74                             PVOID DispatcherContext)
  75
  76       This was found experimentally to always be at offset 56 of the
  77       context frame in all cases handled by this implementation.
  78
  79    3) When we have the signal context we just have to save some registers
  80       and set the return address based on the program counter (Eip).
  81
  82    Note that this implementation follows closely the same principles as the
  83    GNU/Linux and OSF ones.  */
  84
  85 #ifndef __MINGW64__
  86
  87 #define WIN32_MEAN_AND_LEAN
  88 #include <windows.h>
  89 /* Patterns found experimentally to be on a Windows signal handler  */
  90
  91 /* In a standard exception filter  */
  92
  93 #define SIG_PAT1 \
  94       (pc_[-2] == 0xff && pc_[-1] == 0xd0     /* call %eax           */ \
  95       && pc_[0] == 0x83 && pc_[1] == 0xf8)    /* cmp 0xdepl,%eax     */
  96
  97 #define SIG_PAT2 \
  98         (pc_[-5] == 0xe8 && pc_[-4] == 0x68   /* call (depl16)       */ \
  99          && pc_[0] == 0xc3)                   /* ret                 */
 100
 101 /* In a Win32 SEH handler  */
 102
 103 #define SIG_SEH1 \
 104         (pc_[-5] == 0xe8                      /* call addr           */ \
 105          && pc_[0] == 0x83 && pc_[1] == 0xc4  /* add 0xval,%esp      */ \
 106          && pc_[3] == 0xb8)                   /* mov 0xval,%eax      */
 107
 108 #define SIG_SEH2 \
 109         (pc_[-5] == 0x8b && pc_[-4] == 0x4d   /* mov depl(%ebp),%ecx */ \
 110          && pc_[0] == 0x64 && pc_[1] == 0x8b) /* mov %fs:(0),<reg>   */ \
 111
 112 /* In the GCC alloca (stack probing)  */
 113
 114 #define SIG_ALLOCA \
 115           (pc_[-1] == 0x83                    /* orl $0x0,(%ecx)     */ \
 116            && pc_[0] == 0x9 && pc_[1] == 0                              \
 117            && pc_[2] == 0x2d && pc_[3] == 0   /* subl $0x1000,%eax   */ \
 118            && pc_[4] == 0x10 && pc_[5] == 0)
 119
 120
 121 #define MD_FALLBACK_FRAME_STATE_FOR i386_w32_fallback_frame_state
 122
 123 static _Unwind_Reason_Code
 124 i386_w32_fallback_frame_state (struct _Unwind_Context *context,
 125                                _Unwind_FrameState *fs)
 126
 127 {
 128   void * ctx_ra_  = (void *)(context->ra);  /* return address */
 129   void * ctx_cfa_ = (void *)(context->cfa); /* context frame address */
 130   unsigned char * pc_ = (unsigned char *) ctx_ra_;
 131
 132   /* In the test below we look for two specific patterns found
 133      experimentally to be in the Windows signal handler.  */
 134   if (SIG_PAT1 || SIG_PAT2 || SIG_SEH1 || SIG_SEH2)
 135     {
 136       PEXCEPTION_POINTERS weinfo_;
 137       PCONTEXT proc_ctx_;
 138       long new_cfa_;
 139
 140       if (SIG_SEH1)
 141         proc_ctx_ = (PCONTEXT) (*(int*)(ctx_cfa_ + 56));
 142       else if (SIG_SEH2)
 143         proc_ctx_ = (PCONTEXT) (*(int*)(ctx_cfa_ + 8));
 144       else
 145         {
 146           weinfo_ = (PEXCEPTION_POINTERS) (*(int*)ctx_cfa_);
 147           proc_ctx_ = weinfo_->ContextRecord;
 148         }
 149
 150       /* The new context frame address is the stack pointer.  */
 151       new_cfa_ = proc_ctx_->Esp;
 152       fs->regs.cfa_how = CFA_REG_OFFSET;
 153       fs->regs.cfa_reg = __builtin_dwarf_sp_column();
 154       fs->regs.cfa_offset = new_cfa_ - (long) ctx_cfa_;
 155
 156       /* Restore registers.  */
 157       fs->regs.reg[0].how = REG_SAVED_OFFSET;
 158       fs->regs.reg[0].loc.offset = (long)&proc_ctx_->Eax - new_cfa_;
 159       fs->regs.reg[3].how = REG_SAVED_OFFSET;
 160       fs->regs.reg[3].loc.offset = (long)&proc_ctx_->Ebx - new_cfa_;
 161       fs->regs.reg[1].how = REG_SAVED_OFFSET;
 162       fs->regs.reg[1].loc.offset = (long)&proc_ctx_->Ecx - new_cfa_;
 163       fs->regs.reg[2].how = REG_SAVED_OFFSET;
 164       fs->regs.reg[2].loc.offset = (long)&proc_ctx_->Edx - new_cfa_;
 165       fs->regs.reg[6].how = REG_SAVED_OFFSET;
 166       fs->regs.reg[6].loc.offset = (long)&proc_ctx_->Esi - new_cfa_;
 167       fs->regs.reg[7].how = REG_SAVED_OFFSET;
 168       fs->regs.reg[7].loc.offset = (long)&proc_ctx_->Edi - new_cfa_;
 169       fs->regs.reg[5].how = REG_SAVED_OFFSET;
 170       fs->regs.reg[5].loc.offset = (long)&proc_ctx_->Ebp - new_cfa_;
 171       fs->regs.reg[8].how = REG_SAVED_OFFSET;
 172       fs->regs.reg[8].loc.offset = (long)&proc_ctx_->Eip - new_cfa_;
 173       fs->retaddr_column = 8;
 174       fs->signal_frame = 1;
 175
 176       return _URC_NO_REASON;
 177     }
 178
 179   /* Unwinding through _alloca, propagating from a trap triggered by
 180      one of it's probes prior to the real SP adjustment. The only
 181      operations of interest performed is "pushl %ecx", followed by
 182      ecx clobbering.  */
 183   else if (SIG_ALLOCA)
 184     {
 185       /* Only one push between entry in _alloca and the probe trap.  */
 186       long new_cfa_ = (long) ctx_cfa_ + 4;
 187
 188       fs->regs.cfa_how = CFA_REG_OFFSET;
 189       fs->regs.cfa_reg = __builtin_dwarf_sp_column();
 190       fs->regs.cfa_offset = new_cfa_ - (long) ctx_cfa_;
 191
 192       /* The saved value of %ecx is at CFA - 4 */
 193       fs->regs.reg[1].how = REG_SAVED_OFFSET;
 194       fs->regs.reg[1].loc.offset = -4;
 195
 196       /* and what is stored at the CFA is the return address.  */
 197       fs->retaddr_column = 8;
 198       fs->regs.reg[8].how = REG_SAVED_OFFSET;
 199       fs->regs.reg[8].loc.offset = 0;
 200       fs->signal_frame = 1;
 201
 202       return _URC_NO_REASON;
 203     }
 204   else
 205     return _URC_END_OF_STACK;
 206 }
 207
 208 #endif /* !__MINGW64__ */