libjava/exception.cc

   1 // Functions for Exception Support for Java.
   2
   3 /* Copyright (C) 1998, 1999, 2001  Free Software Foundation
   4
   5    This file is part of libgcj.
   6
   7 This software is copyrighted work licensed under the terms of the
   8 Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
   9 details.  */
  10
  11 #include <config.h>
  12
  13 #include <stddef.h>
  14 #include <cstdlib>
  15
  16 #include <java/lang/Class.h>
  17 #include <java/lang/NullPointerException.h>
  18 #include <gcj/cni.h>
  19 #include <jvm.h>
  20
  21 #include "unwind.h"
  22
  23 #include <gc.h>
  24
  25 \f
  26 struct alignment_test_struct
  27 {
  28   char space;
  29   char end[0] __attribute__((aligned));
  30 };
  31
  32 struct java_exception_header
  33 {
  34   /* Cache handler details between Phase 1 and Phase 2.  */
  35   _Unwind_Ptr landingPad;
  36   int handlerSwitchValue;
  37
  38   /* The object being thrown.  Compiled code expects this to be immediately
  39      before the generic exception header.  Which is complicated by the fact
  40      that _Unwind_Exception is ((aligned)).  */
  41
  42   char pad[sizeof(jthrowable) < sizeof(alignment_test_struct)
  43            ? sizeof(alignment_test_struct) - sizeof(jthrowable) : 0]
  44     __attribute__((aligned));
  45
  46   jthrowable value;
  47
  48   /* The generic exception header.  */
  49   _Unwind_Exception unwindHeader;
  50 };
  51
  52 // This is the exception class we report -- "GNUCJAVA".
  53 const _Unwind_Exception_Class __gcj_exception_class
  54 = ((((((((_Unwind_Exception_Class) 'G'
  55          << 8 | (_Unwind_Exception_Class) 'N')
  56         << 8 | (_Unwind_Exception_Class) 'U')
  57        << 8 | (_Unwind_Exception_Class) 'C')
  58       << 8 | (_Unwind_Exception_Class) 'J')
  59      << 8 | (_Unwind_Exception_Class) 'A')
  60     << 8 | (_Unwind_Exception_Class) 'V')
  61    << 8 | (_Unwind_Exception_Class) 'A');
  62
  63
  64 static inline java_exception_header *
  65 get_exception_header_from_ue (_Unwind_Exception *exc)
  66 {
  67   return reinterpret_cast<java_exception_header *>(exc + 1) - 1;
  68 }
  69
  70 /* Perform a throw, Java style. Throw will unwind through this call,
  71    so there better not be any handlers or exception thrown here. */
  72
  73 extern "C" void
  74 _Jv_Throw (jthrowable value)
  75 {
  76   /* FIXME: Use the proper API to the collector.  */
  77   java_exception_header *xh
  78     = static_cast<java_exception_header *>(GC_malloc (sizeof (*xh)));
  79
  80   if (value == NULL)
  81     value = new java::lang::NullPointerException ();
  82   xh->value = value;
  83
  84   xh->unwindHeader.exception_class = __gcj_exception_class;
  85   xh->unwindHeader.exception_cleanup = NULL;
  86
  87   /* We're happy with setjmp/longjmp exceptions or region-based
  88      exception handlers: entry points are provided here for both.  */
  89   _Unwind_Reason_Code code;
  90 #ifdef SJLJ_EXCEPTIONS
  91   code = _Unwind_SjLj_RaiseException (&xh->unwindHeader);
  92 #else
  93   code = _Unwind_RaiseException (&xh->unwindHeader);
  94 #endif
  95
  96   /* If code == _URC_END_OF_STACK, then we reached top of stack without
  97      finding a handler for the exception.  Since each thread is run in
  98      a try/catch, this oughtn't happen.  If code is something else, we
  99      encountered some sort of heinous lossage from which we could not
 100      recover.  As is the way of such things, almost certainly we will have
 101      crashed before now, rather than actually being able to diagnose the
 102      problem.  */
 103   std::abort ();
 104 }
 105
 106 \f
 107 #include "unwind-pe.h"
 108 \f
 109 struct lsda_header_info
 110 {
 111   _Unwind_Ptr Start;
 112   _Unwind_Ptr LPStart;
 113   const unsigned char *TType;
 114   const unsigned char *action_table;
 115   unsigned char ttype_encoding;
 116   unsigned char call_site_encoding;
 117 };
 118
 119 static const unsigned char *
 120 parse_lsda_header (_Unwind_Context *context, const unsigned char *p,
 121                    lsda_header_info *info)
 122 {
 123   _Unwind_Word tmp;
 124   unsigned char lpstart_encoding;
 125
 126   info->Start = (context ? _Unwind_GetRegionStart (context) : 0);
 127
 128   // Find @LPStart, the base to which landing pad offsets are relative.
 129   lpstart_encoding = *p++;
 130   if (lpstart_encoding != DW_EH_PE_omit)
 131     p = read_encoded_value (context, lpstart_encoding, p, &info->LPStart);
 132   else
 133     info->LPStart = info->Start;
 134
 135   // Find @TType, the base of the handler and exception spec type data.
 136   info->ttype_encoding = *p++;
 137   if (info->ttype_encoding != DW_EH_PE_omit)
 138     {
 139       p = read_uleb128 (p, &tmp);
 140       info->TType = p + tmp;
 141     }
 142   else
 143     info->TType = 0;
 144
 145   // The encoding and length of the call-site table; the action table
 146   // immediately follows.
 147   info->call_site_encoding = *p++;
 148   p = read_uleb128 (p, &tmp);
 149   info->action_table = p + tmp;
 150
 151   return p;
 152 }
 153
 154 static jclass
 155 get_ttype_entry (_Unwind_Context *context, lsda_header_info *info, long i)
 156 {
 157   _Unwind_Ptr ptr;
 158
 159   i *= size_of_encoded_value (info->ttype_encoding);
 160   read_encoded_value (context, info->ttype_encoding, info->TType - i, &ptr);
 161
 162   return reinterpret_cast<jclass>(ptr);
 163 }
 164
 165
 166 // Using a different personality function name causes link failures
 167 // when trying to mix code using different exception handling models.
 168 #ifdef SJLJ_EXCEPTIONS
 169 #define PERSONALITY_FUNCTION    __gcj_personality_sj0
 170 #define __builtin_eh_return_data_regno(x) x
 171 #else
 172 #define PERSONALITY_FUNCTION    __gcj_personality_v0
 173 #endif
 174
 175 extern "C" _Unwind_Reason_Code
 176 PERSONALITY_FUNCTION (int version,
 177                       _Unwind_Action actions,
 178                       _Unwind_Exception_Class exception_class,
 179                       struct _Unwind_Exception *ue_header,
 180                       struct _Unwind_Context *context)
 181 {
 182   java_exception_header *xh = get_exception_header_from_ue (ue_header);
 183
 184   lsda_header_info info;
 185   const unsigned char *language_specific_data;
 186   const unsigned char *action_record;
 187   const unsigned char *p;
 188   _Unwind_Ptr landing_pad, ip;
 189   int handler_switch_value;
 190   bool saw_cleanup;
 191   bool saw_handler;
 192
 193
 194   // Interface version check.
 195   if (version != 1)
 196     return _URC_FATAL_PHASE1_ERROR;
 197
 198   // Shortcut for phase 2 found handler for domestic exception.
 199   if (actions == (_UA_CLEANUP_PHASE | _UA_HANDLER_FRAME)
 200       && exception_class == __gcj_exception_class)
 201     {
 202       handler_switch_value = xh->handlerSwitchValue;
 203       landing_pad = xh->landingPad;
 204       goto install_context;
 205     }
 206
 207   // FIXME: In Phase 1, record _Unwind_GetIP in xh->obj as a part of
 208   // the stack trace for this exception.  This will only collect Java
 209   // frames, but perhaps that is acceptable.
 210   // FIXME2: _Unwind_GetIP is nonsensical for SJLJ, being a call-site
 211   // index instead of a PC value.  We could perhaps arrange for
 212   // _Unwind_GetRegionStart to return context->fc->jbuf[1], which
 213   // is the address of the handler label for __builtin_longjmp, but
 214   // there is no solution for DONT_USE_BUILTIN_SETJMP.
 215
 216   language_specific_data = (const unsigned char *)
 217     _Unwind_GetLanguageSpecificData (context);
 218
 219   // If no LSDA, then there are no handlers or cleanups.
 220   if (! language_specific_data)
 221     return _URC_CONTINUE_UNWIND;
 222
 223   // Parse the LSDA header.
 224   p = parse_lsda_header (context, language_specific_data, &info);
 225   ip = _Unwind_GetIP (context) - 1;
 226   landing_pad = 0;
 227   action_record = 0;
 228   handler_switch_value = 0;
 229
 230 #ifdef SJLJ_EXCEPTIONS
 231   // The given "IP" is an index into the call-site table, with two
 232   // exceptions -- -1 means no-action, and 0 means terminate.  But
 233   // since we're using uleb128 values, we've not got random access
 234   // to the array.
 235   if ((int) ip <= 0)
 236     return _URC_CONTINUE_UNWIND;
 237   else
 238     {
 239       _Unwind_Word cs_lp, cs_action;
 240       do
 241         {
 242           p = read_uleb128 (p, &cs_lp);
 243           p = read_uleb128 (p, &cs_action);
 244         }
 245       while (--ip);
 246
 247       // Can never have null landing pad for sjlj -- that would have
 248       // been indicated by a -1 call site index.
 249       landing_pad = cs_lp + 1;
 250       if (cs_action)
 251         action_record = info.action_table + cs_action - 1;
 252       goto found_something;
 253     }
 254 #else
 255   // Search the call-site table for the action associated with this IP.
 256   while (p < info.action_table)
 257     {
 258       _Unwind_Ptr cs_start, cs_len, cs_lp;
 259       _Unwind_Word cs_action;
 260
 261       // Note that all call-site encodings are "absolute" displacements.
 262       p = read_encoded_value (0, info.call_site_encoding, p, &cs_start);
 263       p = read_encoded_value (0, info.call_site_encoding, p, &cs_len);
 264       p = read_encoded_value (0, info.call_site_encoding, p, &cs_lp);
 265       p = read_uleb128 (p, &cs_action);
 266
 267       // The table is sorted, so if we've passed the ip, stop.
 268       if (ip < info.Start + cs_start)
 269         p = info.action_table;
 270       else if (ip < info.Start + cs_start + cs_len)
 271         {
 272           if (cs_lp)
 273             landing_pad = info.LPStart + cs_lp;
 274           if (cs_action)
 275             action_record = info.action_table + cs_action - 1;
 276           goto found_something;
 277         }
 278     }
 279 #endif // SJLJ_EXCEPTIONS
 280
 281   // If ip is not present in the table, C++ would call terminate.
 282   // ??? It is perhaps better to tweek the LSDA so that no-action
 283   // is mapped to no-entry for Java.
 284   return _URC_CONTINUE_UNWIND;
 285
 286  found_something:
 287   saw_cleanup = false;
 288   saw_handler = false;
 289
 290   if (landing_pad == 0)
 291     {
 292       // If ip is present, and has a null landing pad, there are
 293       // no cleanups or handlers to be run.
 294     }
 295   else if (action_record == 0)
 296     {
 297       // If ip is present, has a non-null landing pad, and a null
 298       // action table offset, then there are only cleanups present.
 299       // Cleanups use a zero switch value, as set above.
 300       saw_cleanup = true;
 301     }
 302   else
 303     {
 304       // Otherwise we have a catch handler.
 305       _Unwind_Sword ar_filter, ar_disp;
 306
 307       while (1)
 308         {
 309           p = action_record;
 310           p = read_sleb128 (p, &ar_filter);
 311           read_sleb128 (p, &ar_disp);
 312
 313           if (ar_filter == 0)
 314             {
 315               // Zero filter values are cleanups.
 316               saw_cleanup = true;
 317             }
 318
 319           // During forced unwinding, we only run cleanups.  With a
 320           // foreign exception class, we have no class info to match.
 321           else if ((actions & _UA_FORCE_UNWIND)
 322               || exception_class != __gcj_exception_class)
 323             ;
 324
 325           else if (ar_filter > 0)
 326             {
 327               // Positive filter values are handlers.
 328
 329               jclass catch_type = get_ttype_entry (context, &info, ar_filter);
 330
 331               // The catch_type is either a (java::lang::Class*) or
 332               // is one more than a (Utf8Const*).
 333               if ((size_t)catch_type & 1)
 334                 catch_type = _Jv_FindClass ((Utf8Const*)catch_type - 1, NULL);
 335
 336               if (_Jv_IsInstanceOf (xh->value, catch_type))
 337                 {
 338                   handler_switch_value = ar_filter;
 339                   saw_handler = true;
 340                   break;
 341                 }
 342             }
 343           else
 344             {
 345               // Negative filter values are exception specifications,
 346               // which Java does not use.
 347               // ??? Perhaps better to make them an index into a table
 348               // of null-terminated strings instead of playing games
 349               // with Utf8Const+1 as above.
 350               std::abort ();
 351             }
 352
 353           if (ar_disp == 0)
 354             break;
 355           action_record = p + ar_disp;
 356         }
 357     }
 358
 359   if (! saw_handler && ! saw_cleanup)
 360     return _URC_CONTINUE_UNWIND;
 361
 362   if (actions & _UA_SEARCH_PHASE)
 363     {
 364       if (! saw_handler)
 365         return _URC_CONTINUE_UNWIND;
 366
 367       // For domestic exceptions, we cache data from phase 1 for phase 2.
 368       if (exception_class == __gcj_exception_class)
 369         {
 370           xh->handlerSwitchValue = handler_switch_value;
 371           xh->landingPad = landing_pad;
 372         }
 373       return _URC_HANDLER_FOUND;
 374     }
 375
 376  install_context:
 377   _Unwind_SetGR (context, __builtin_eh_return_data_regno (0),
 378                  (_Unwind_Ptr) &xh->unwindHeader);
 379   _Unwind_SetGR (context, __builtin_eh_return_data_regno (1),
 380                  handler_switch_value);
 381   _Unwind_SetIP (context, landing_pad);
 382   return _URC_INSTALL_CONTEXT;
 383 }