libgcc/unwind-seh.c

   1 /* Structured Exception Handling (SEH) runtime interface routines.
   2    Copyright (C) 2010-2020 Free Software Foundation, Inc.
   3
   4    This file is part of GCC.
   5
   6    GCC is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3, or (at your option)
   9    any later version.
  10
  11    GCC is distributed in the hope that it will be useful, but WITHOUT
  12    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  13    or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
  14    License for more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 #include "tconfig.h"
  26 #include "tsystem.h"
  27 #include "coretypes.h"
  28 #include "tm.h"
  29 #include "unwind.h"
  30
  31 #if defined (__SEH__) && !defined (__USING_SJLJ_EXCEPTIONS__)
  32
  33 /* At the moment everything is written for x64, but in theory this could
  34    also be used for i386, arm, mips and other extant embedded Windows.  */
  35 #ifndef __x86_64__
  36 #error "Unsupported architecture."
  37 #endif
  38 \f
  39 /* Define GCC's exception codes.  See
  40      http://msdn.microsoft.com/en-us/library/het71c37(v=VS.80).aspx
  41    In particular, MS defines bits:
  42      [31:30] = 3 (error), 2 (warning), 1 (info), 0 (success)
  43      [29]    = 1 (user-defined)
  44      [28]    = 0 (reserved)
  45    We define bits:
  46      [24:27] = type
  47      [0:23]  = magic
  48    We set "magic" to "GCC", which is similar to MVC++ which uses "msc"
  49    as the low 3 bytes of its user-defined codes for C++ exceptions.
  50
  51    We define the ExceptionInformation entries as follows:
  52      [0] = _Unwind_Exception pointer
  53      [1] = target frame
  54      [2] = target ip
  55      [3] = target rdx
  56 */
  57
  58 #define STATUS_USER_DEFINED             (1U << 29)
  59
  60 #define GCC_MAGIC                       (('G' << 16) | ('C' << 8) | 'C')
  61 #define GCC_EXCEPTION(TYPE)             \
  62        (STATUS_USER_DEFINED | ((TYPE) << 24) | GCC_MAGIC)
  63
  64 #define STATUS_GCC_THROW                GCC_EXCEPTION (0)
  65 #define STATUS_GCC_UNWIND               GCC_EXCEPTION (1)
  66 #define STATUS_GCC_FORCED               GCC_EXCEPTION (2)
  67
  68 \f
  69 struct _Unwind_Context
  70 {
  71   _Unwind_Word cfa;
  72   _Unwind_Word ra;
  73   _Unwind_Word reg[2];
  74   PDISPATCHER_CONTEXT disp;
  75 };
  76
  77 /* Get the value of register INDEX as saved in CONTEXT.  */
  78
  79 _Unwind_Word
  80 _Unwind_GetGR (struct _Unwind_Context *c, int index)
  81 {
  82   if (index < 0 || index >= 2)
  83     abort ();
  84   return c->reg[index];
  85 }
  86
  87 /* Overwrite the saved value for register INDEX in CONTEXT with VAL.  */
  88
  89 void
  90 _Unwind_SetGR (struct _Unwind_Context *c, int index, _Unwind_Word val)
  91 {
  92   if (index < 0 || index >= 2)
  93     abort ();
  94   c->reg[index] = val;
  95 }
  96
  97 /* Get the value of the CFA as saved in CONTEXT.  */
  98
  99 _Unwind_Word
 100 _Unwind_GetCFA (struct _Unwind_Context *c)
 101 {
 102   return c->cfa;
 103 }
 104
 105 /* Retrieve the return address for CONTEXT.  */
 106
 107 _Unwind_Ptr
 108 _Unwind_GetIP (struct _Unwind_Context *c)
 109 {
 110   return c->ra;
 111 }
 112
 113 /* Retrieve the return address and flag whether that IP is before
 114    or after first not yet fully executed instruction.  */
 115
 116 _Unwind_Ptr
 117 _Unwind_GetIPInfo (struct _Unwind_Context *c, int *ip_before_insn)
 118 {
 119   /* ??? Is there a concept of a signal context properly?  There's
 120      obviously an UNWP_PUSH_MACHFRAME opcode, but the runtime might
 121      have arranged for that not to matter, really.  */
 122   *ip_before_insn = 0;
 123   return c->ra;
 124 }
 125
 126 /* Overwrite the return address for CONTEXT with VAL.  */
 127
 128 void
 129 _Unwind_SetIP (struct _Unwind_Context *c, _Unwind_Ptr val)
 130 {
 131   c->ra = val;
 132 }
 133
 134 void *
 135 _Unwind_GetLanguageSpecificData (struct _Unwind_Context *c)
 136 {
 137   return c->disp->HandlerData;
 138 }
 139
 140 _Unwind_Ptr
 141 _Unwind_GetRegionStart (struct _Unwind_Context *c)
 142 {
 143   return c->disp->FunctionEntry->BeginAddress + c->disp->ImageBase;
 144 }
 145
 146 void *
 147 _Unwind_FindEnclosingFunction (void *pc)
 148 {
 149   PRUNTIME_FUNCTION entry;
 150   ULONG64 ImageBase;
 151
 152   entry = RtlLookupFunctionEntry ((ULONG64)pc, &ImageBase, NULL);
 153
 154   return (entry ? (void *)(entry->BeginAddress + ImageBase) : NULL);
 155 }
 156
 157 _Unwind_Ptr
 158 _Unwind_GetDataRelBase (struct _Unwind_Context *c ATTRIBUTE_UNUSED)
 159 {
 160   return 0;
 161 }
 162
 163 _Unwind_Ptr
 164 _Unwind_GetTextRelBase (struct _Unwind_Context *c)
 165 {
 166   return c->disp->ImageBase;
 167 }
 168
 169 \f
 170 /* The two-phase unwind process that GCC uses is ordered differently
 171    from the two-phase unwind process that SEH uses.  The mechansism
 172    that GCC uses is to have the filter return _URC_HANDER_FOUND; the
 173    mechanism that SEH uses is for the filter function call back into
 174    the unwinder.
 175
 176    An Ideal port to SEH would have GCC emit handler functions that
 177    can be called, given a pointer to the "EstablisherFrame" (i.e.
 178    the frame pointer base of the user-level function) can manipulate
 179    the user-level variables within the user-level function's stack
 180    frame.  Once done manipulating the variables, it would return
 181    a ExceptionContinueSearch, and the unwind process would continue.
 182
 183    GCC has always done things a bit differently.  We continue to
 184    transfer control back into the user-level function which, once
 185    done manipulating the user-level variables, re-throws the exception.  */
 186
 187 /* The "real" language-specific personality handler forwards to here
 188    where we handle the MS SEH state and transforms it into the GCC
 189    unwind state as per GCC's <unwind.h>, at which point we defer to
 190    the regular language-specfic exception handler, which is passed in.  */
 191
 192 EXCEPTION_DISPOSITION
 193 _GCC_specific_handler (PEXCEPTION_RECORD ms_exc, void *this_frame,
 194                        PCONTEXT ms_orig_context, PDISPATCHER_CONTEXT ms_disp,
 195                        _Unwind_Personality_Fn gcc_per)
 196 {
 197   DWORD ms_flags = ms_exc->ExceptionFlags;
 198   DWORD ms_code = ms_exc->ExceptionCode;
 199
 200   struct _Unwind_Exception *gcc_exc
 201     = (struct _Unwind_Exception *) ms_exc->ExceptionInformation[0];
 202   struct _Unwind_Context gcc_context;
 203   _Unwind_Action gcc_action;
 204   _Unwind_Reason_Code gcc_reason;
 205
 206   if (ms_flags & EXCEPTION_TARGET_UNWIND)
 207     {
 208       /* This frame is known to be the target frame.  We've already
 209          "installed" the target_ip and RAX value via the arguments
 210          to RtlUnwindEx.  All that's left is to set the RDX value
 211          and "continue" to have the context installed.  */
 212       ms_disp->ContextRecord->Rdx = ms_exc->ExceptionInformation[3];
 213       return ExceptionContinueSearch;
 214     }
 215
 216   if (ms_code == STATUS_GCC_UNWIND)
 217     {
 218       /* This is a colliding exception that we threw so that we could
 219          cancel the already in-flight exception and stop in a frame
 220          that wanted to perform some unwind action.  The only relevant
 221          test is that we're the target frame.  */
 222       if (ms_exc->ExceptionInformation[1] == (_Unwind_Ptr) this_frame)
 223         {
 224           RtlUnwindEx (this_frame, (PVOID) ms_exc->ExceptionInformation[2],
 225                        ms_exc, gcc_exc, ms_orig_context,
 226                        ms_disp->HistoryTable);
 227           abort ();
 228         }
 229       return ExceptionContinueSearch;
 230     }
 231
 232   gcc_context.cfa = ms_disp->ContextRecord->Rsp;
 233   gcc_context.ra = ms_disp->ControlPc;
 234   gcc_context.reg[0] = 0xdeadbeef;      /* These are write-only.  */
 235   gcc_context.reg[1] = 0xdeadbeef;
 236   gcc_context.disp = ms_disp;
 237
 238   if (ms_code == STATUS_GCC_FORCED)
 239     {
 240        _Unwind_Stop_Fn stop = (_Unwind_Stop_Fn) gcc_exc->private_[0];
 241        void *stop_argument = (void *) gcc_exc->private_[4];
 242
 243        gcc_action = _UA_FORCE_UNWIND | _UA_CLEANUP_PHASE;
 244
 245        stop (1, gcc_action, gcc_exc->exception_class, gcc_exc,
 246              &gcc_context, stop_argument);
 247
 248        goto phase2;
 249     }
 250
 251   /* ??? TODO: handling non-gcc user-defined exceptions as foreign.  */
 252   if (ms_code != STATUS_GCC_THROW)
 253     return ExceptionContinueSearch;
 254
 255   if (ms_flags & (EXCEPTION_UNWINDING | EXCEPTION_EXIT_UNWIND))
 256     {
 257       /* This is Phase 2.  */
 258       /* We know this isn't the target frame because we've already tested
 259          EXCEPTION_TARGET_UNWIND.  The remaining possibility is that the
 260          gcc personality has unwind code to run.  */
 261
 262       gcc_action = _UA_CLEANUP_PHASE;
 263     phase2:
 264       gcc_reason = gcc_per (1, gcc_action, gcc_exc->exception_class,
 265                             gcc_exc, &gcc_context);
 266
 267       if (gcc_reason == _URC_CONTINUE_UNWIND)
 268         return ExceptionContinueSearch;
 269
 270       if (gcc_reason == _URC_INSTALL_CONTEXT)
 271         {
 272           /* Scratch space for the bits for the unwind catch.  */
 273           ms_exc->ExceptionInformation[1] = (_Unwind_Ptr) this_frame;
 274           ms_exc->ExceptionInformation[2] = gcc_context.ra;
 275           ms_exc->ExceptionInformation[3] = gcc_context.reg[1];
 276
 277           /* Cancel the current exception by raising another.  */
 278           RaiseException (STATUS_GCC_UNWIND, EXCEPTION_NONCONTINUABLE,
 279                           4, ms_exc->ExceptionInformation);
 280
 281           /* Is RaiseException declared noreturn?  */
 282         }
 283
 284       /* In _Unwind_RaiseException_Phase2 we return _URC_FATAL_PHASE2_ERROR. */
 285     }
 286   else
 287     {
 288       /* This is Phase 1.  */
 289       gcc_reason = gcc_per (1, _UA_SEARCH_PHASE, gcc_exc->exception_class,
 290                             gcc_exc, &gcc_context);
 291
 292       if (gcc_reason == _URC_CONTINUE_UNWIND)
 293         return ExceptionContinueSearch;
 294
 295       if (gcc_reason == _URC_HANDLER_FOUND)
 296         {
 297           /* We really need some of the information that GCC's personality
 298              routines compute during phase 2 right now, like the target IP.
 299              Go ahead and ask for it now, and cache it.  */
 300           gcc_reason = gcc_per (1, _UA_CLEANUP_PHASE | _UA_HANDLER_FRAME,
 301                                 gcc_exc->exception_class, gcc_exc,
 302                                 &gcc_context);
 303           if (gcc_reason != _URC_INSTALL_CONTEXT)
 304             abort ();
 305
 306           gcc_exc->private_[1] = (_Unwind_Ptr) this_frame;
 307           gcc_exc->private_[2] = gcc_context.ra;
 308           gcc_exc->private_[3] = gcc_context.reg[1];
 309
 310           ms_exc->NumberParameters = 4;
 311           ms_exc->ExceptionInformation[1] = (_Unwind_Ptr) this_frame;
 312           ms_exc->ExceptionInformation[2] = gcc_context.ra;
 313           ms_exc->ExceptionInformation[3] = gcc_context.reg[1];
 314
 315           /* Begin phase 2.  Perform the unwinding.  */
 316           RtlUnwindEx (this_frame, (PVOID)gcc_context.ra, ms_exc,
 317                        (PVOID)gcc_context.reg[0], ms_orig_context,
 318                        ms_disp->HistoryTable);
 319         }
 320
 321       /* In _Unwind_RaiseException we return _URC_FATAL_PHASE1_ERROR.  */
 322     }
 323   abort ();
 324 }
 325
 326 /* Raise an exception, passing along the given exception object.  */
 327
 328 _Unwind_Reason_Code
 329 _Unwind_RaiseException (struct _Unwind_Exception *exc)
 330 {
 331   memset (exc->private_, 0, sizeof (exc->private_));
 332
 333   /* The ExceptionInformation array will have only 1 element, EXC.  */
 334   RaiseException (STATUS_GCC_THROW, 0, 1, (ULONG_PTR *)&exc);
 335
 336   /* The exception handler installed in crt0 will continue any GCC
 337      exception that reaches there (and isn't marked non-continuable).
 338      Returning allows the C++ runtime to call std::terminate.  */
 339   return _URC_END_OF_STACK;
 340 }
 341
 342 /* Resume propagation of an existing exception.  This is used after
 343    e.g. executing cleanup code, and not to implement rethrowing.  */
 344
 345 void
 346 _Unwind_Resume (struct _Unwind_Exception *gcc_exc)
 347 {
 348   UNWIND_HISTORY_TABLE ms_history;
 349   EXCEPTION_RECORD ms_exc;
 350   CONTEXT ms_context;
 351
 352   memset (&ms_exc, 0, sizeof(ms_exc));
 353   memset (&ms_history, 0, sizeof(ms_history));
 354
 355   /* ??? Not 100% perfect, since we aren't passing on the *original*
 356      exception context, but should be good enough.  */
 357   ms_exc.ExceptionCode = STATUS_GCC_THROW;
 358   ms_exc.ExceptionFlags = EXCEPTION_NONCONTINUABLE;
 359   ms_exc.NumberParameters = 4;
 360   ms_exc.ExceptionInformation[0] = (ULONG_PTR) gcc_exc;
 361   ms_exc.ExceptionInformation[1] = gcc_exc->private_[1];
 362   ms_exc.ExceptionInformation[2] = gcc_exc->private_[2];
 363   ms_exc.ExceptionInformation[3] = gcc_exc->private_[3];
 364
 365   ms_context.ContextFlags = CONTEXT_ALL;
 366   RtlCaptureContext (&ms_context);
 367
 368   RtlUnwindEx ((void *) gcc_exc->private_[1], (PVOID)gcc_exc->private_[2],
 369                &ms_exc, gcc_exc, &ms_context, &ms_history);
 370
 371   /* Is RtlUnwindEx declared noreturn?  */
 372   abort ();
 373 }
 374
 375 static _Unwind_Reason_Code
 376 _Unwind_ForcedUnwind_Phase2 (struct _Unwind_Exception *exc)
 377 {
 378   _Unwind_Stop_Fn stop;
 379   void * stop_argument;
 380
 381   RaiseException (STATUS_GCC_FORCED, 0, 1, (ULONG_PTR *)&exc);
 382
 383   /* If we get here, we got to top-of-stack.  */
 384   /* ??? We no longer have a context pointer to pass in.  */
 385
 386   stop = (_Unwind_Stop_Fn) exc->private_[0];
 387   stop_argument = (void *) exc->private_[4];
 388   stop (1, _UA_FORCE_UNWIND | _UA_CLEANUP_PHASE | _UA_END_OF_STACK,
 389         exc->exception_class, exc, NULL, stop_argument);
 390
 391   return _UA_END_OF_STACK;
 392 }
 393
 394 _Unwind_Reason_Code
 395 _Unwind_Resume_or_Rethrow (struct _Unwind_Exception *exc)
 396 {
 397   if (exc->private_[0] == 0)
 398     _Unwind_RaiseException (exc);
 399   else
 400     _Unwind_ForcedUnwind_Phase2 (exc);
 401   abort ();
 402 }
 403
 404 /* Raise an exception for forced unwinding.  */
 405
 406 _Unwind_Reason_Code
 407 _Unwind_ForcedUnwind (struct _Unwind_Exception *exc,
 408                       _Unwind_Stop_Fn stop, void * stop_argument)
 409 {
 410   /* ??? This is a hack that only works with _GCC_specific_handler.
 411      There's no way to invoke STOP within frames that use a different
 412      exception handler.  This is essentially just good enough to run
 413      the code within the gcc testsuite.  */
 414
 415   memset (exc->private_, 0, sizeof (exc->private_));
 416   exc->private_[0] = (_Unwind_Ptr) stop;
 417   exc->private_[4] = (_Unwind_Ptr) stop_argument;
 418
 419   return _Unwind_ForcedUnwind_Phase2 (exc);
 420 }
 421
 422 /* A convenience function that calls the exception_cleanup field.  */
 423
 424 void
 425 _Unwind_DeleteException (struct _Unwind_Exception *exc)
 426 {
 427   if (exc->exception_cleanup)
 428     (*exc->exception_cleanup) (_URC_FOREIGN_EXCEPTION_CAUGHT, exc);
 429 }
 430
 431 /* Perform stack backtrace through unwind data.  */
 432
 433 _Unwind_Reason_Code
 434 _Unwind_Backtrace(_Unwind_Trace_Fn trace,
 435                   void *trace_argument)
 436 {
 437   UNWIND_HISTORY_TABLE ms_history;
 438   CONTEXT ms_context;
 439   struct _Unwind_Context gcc_context;
 440   DISPATCHER_CONTEXT disp_context;
 441
 442   memset (&ms_history, 0, sizeof(ms_history));
 443   memset (&gcc_context, 0, sizeof(gcc_context));
 444   memset (&disp_context, 0, sizeof(disp_context));
 445
 446   ms_context.ContextFlags = CONTEXT_ALL;
 447   RtlCaptureContext (&ms_context);
 448
 449   gcc_context.disp = &disp_context;
 450   gcc_context.disp->ContextRecord = &ms_context;
 451   gcc_context.disp->HistoryTable = &ms_history;
 452
 453   while (1)
 454     {
 455       gcc_context.disp->ControlPc = ms_context.Rip;
 456       gcc_context.disp->FunctionEntry
 457         = RtlLookupFunctionEntry (ms_context.Rip, &gcc_context.disp->ImageBase,
 458                                   &ms_history);
 459
 460       if (!gcc_context.disp->FunctionEntry)
 461         return _URC_END_OF_STACK;
 462
 463       gcc_context.disp->LanguageHandler
 464         = RtlVirtualUnwind (0, gcc_context.disp->ImageBase, ms_context.Rip,
 465                             gcc_context.disp->FunctionEntry, &ms_context,
 466                             &gcc_context.disp->HandlerData,
 467                             &gcc_context.disp->EstablisherFrame, NULL);
 468
 469       /* Call trace function.  */
 470       if (trace (&gcc_context, trace_argument) != _URC_NO_REASON)
 471         return _URC_FATAL_PHASE1_ERROR;
 472
 473       /* ??? Check for invalid stack pointer.  */
 474       if (ms_context.Rip == 0)
 475         return _URC_END_OF_STACK;
 476     }
 477 }
 478 #endif /* __SEH__  && !defined (__USING_SJLJ_EXCEPTIONS__)  */