libgcc/config/i386/w32-unwind.h

   1 /* Definitions for Dwarf2 EH unwind support for Windows32 targets
   2    Copyright (C) 2007-2024 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__ */