gcc/c-pragma.c

   1 /* Handle #pragma, system V.4 style.  Supports #pragma weak and #pragma pack.
   2    Copyright (C) 1992, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004
   3    Free Software Foundation, Inc.
   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 2, 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 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING.  If not, write to the Free
  19 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
  20 02111-1307, USA.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tm.h"
  26 #include "rtl.h"
  27 #include "tree.h"
  28 #include "function.h"
  29 #include "cpplib.h"
  30 #include "c-pragma.h"
  31 #include "flags.h"
  32 #include "toplev.h"
  33 #include "ggc.h"
  34 #include "c-common.h"
  35 #include "output.h"
  36 #include "tm_p.h"
  37 #include "target.h"
  38
  39 #define GCC_BAD(msgid) do { warning (msgid); return; } while (0)
  40 #define GCC_BAD2(msgid, arg) do { warning (msgid, arg); return; } while (0)
  41
  42 typedef struct align_stack GTY(())
  43 {
  44   int                  alignment;
  45   unsigned int         num_pushes;
  46   tree                 id;
  47   struct align_stack * prev;
  48 } align_stack;
  49
  50 static GTY(()) struct align_stack * alignment_stack;
  51
  52 #ifdef HANDLE_PRAGMA_PACK
  53 static void handle_pragma_pack (cpp_reader *);
  54
  55 #ifdef HANDLE_PRAGMA_PACK_PUSH_POP
  56 /* If we have a "global" #pragma pack(<n>) in effect when the first
  57    #pragma pack(push,<n>) is encountered, this stores the value of
  58    maximum_field_alignment in effect.  When the final pop_alignment()
  59    happens, we restore the value to this, not to a value of 0 for
  60    maximum_field_alignment.  Value is in bits.  */
  61 static int default_alignment;
  62 #define SET_GLOBAL_ALIGNMENT(ALIGN) \
  63   (default_alignment = maximum_field_alignment = (ALIGN))
  64
  65 static void push_alignment (int, tree);
  66 static void pop_alignment (tree);
  67
  68 /* Push an alignment value onto the stack.  */
  69 static void
  70 push_alignment (int alignment, tree id)
  71 {
  72   if (alignment_stack == NULL
  73       || alignment_stack->alignment != alignment
  74       || id != NULL_TREE)
  75     {
  76       align_stack * entry;
  77
  78       entry = ggc_alloc (sizeof (* entry));
  79
  80       entry->alignment  = alignment;
  81       entry->num_pushes = 1;
  82       entry->id         = id;
  83       entry->prev       = alignment_stack;
  84
  85       /* The current value of maximum_field_alignment is not necessarily
  86          0 since there may be a #pragma pack(<n>) in effect; remember it
  87          so that we can restore it after the final #pragma pop().  */
  88       if (alignment_stack == NULL)
  89         default_alignment = maximum_field_alignment;
  90
  91       alignment_stack = entry;
  92
  93       maximum_field_alignment = alignment;
  94     }
  95   else
  96     alignment_stack->num_pushes ++;
  97 }
  98
  99 /* Undo a push of an alignment onto the stack.  */
 100 static void
 101 pop_alignment (tree id)
 102 {
 103   align_stack * entry;
 104
 105   if (alignment_stack == NULL)
 106     {
 107       warning ("\
 108 #pragma pack (pop) encountered without matching #pragma pack (push, <n>)"
 109                );
 110       return;
 111     }
 112
 113   /* If we got an identifier, strip away everything above the target
 114      entry so that the next step will restore the state just below it.  */
 115   if (id)
 116     {
 117       for (entry = alignment_stack; entry; entry = entry->prev)
 118         if (entry->id == id)
 119           {
 120             entry->num_pushes = 1;
 121             alignment_stack = entry;
 122             break;
 123           }
 124       if (entry == NULL)
 125         warning ("\
 126 #pragma pack(pop, %s) encountered without matching #pragma pack(push, %s, <n>)"
 127                  , IDENTIFIER_POINTER (id), IDENTIFIER_POINTER (id));
 128     }
 129
 130   if (-- alignment_stack->num_pushes == 0)
 131     {
 132       entry = alignment_stack->prev;
 133
 134       if (entry == NULL)
 135         maximum_field_alignment = default_alignment;
 136       else
 137         maximum_field_alignment = entry->alignment;
 138
 139       alignment_stack = entry;
 140     }
 141 }
 142 #else  /* not HANDLE_PRAGMA_PACK_PUSH_POP */
 143 #define SET_GLOBAL_ALIGNMENT(ALIGN) (maximum_field_alignment = (ALIGN))
 144 #define push_alignment(ID, N) \
 145     GCC_BAD("#pragma pack(push[, id], <n>) is not supported on this target")
 146 #define pop_alignment(ID) \
 147     GCC_BAD("#pragma pack(pop[, id], <n>) is not supported on this target")
 148 #endif /* HANDLE_PRAGMA_PACK_PUSH_POP */
 149
 150 /* #pragma pack ()
 151    #pragma pack (N)
 152
 153    #pragma pack (push, N)
 154    #pragma pack (push, ID, N)
 155    #pragma pack (pop)
 156    #pragma pack (pop, ID) */
 157 static void
 158 handle_pragma_pack (cpp_reader *dummy ATTRIBUTE_UNUSED)
 159 {
 160   tree x, id = 0;
 161   int align = -1;
 162   enum cpp_ttype token;
 163   enum { set, push, pop } action;
 164
 165   if (c_lex (&x) != CPP_OPEN_PAREN)
 166     GCC_BAD ("missing '(' after '#pragma pack' - ignored");
 167
 168   token = c_lex (&x);
 169   if (token == CPP_CLOSE_PAREN)
 170     {
 171       action = set;
 172       align = 0;
 173     }
 174   else if (token == CPP_NUMBER)
 175     {
 176       align = TREE_INT_CST_LOW (x);
 177       action = set;
 178       if (c_lex (&x) != CPP_CLOSE_PAREN)
 179         GCC_BAD ("malformed '#pragma pack' - ignored");
 180     }
 181   else if (token == CPP_NAME)
 182     {
 183 #define GCC_BAD_ACTION do { if (action == push) \
 184           GCC_BAD ("malformed '#pragma pack(push[, id], <n>)' - ignored"); \
 185         else \
 186           GCC_BAD ("malformed '#pragma pack(pop[, id])' - ignored"); \
 187         } while (0)
 188
 189       const char *op = IDENTIFIER_POINTER (x);
 190       if (!strcmp (op, "push"))
 191         action = push;
 192       else if (!strcmp (op, "pop"))
 193         action = pop;
 194       else
 195         GCC_BAD2 ("unknown action '%s' for '#pragma pack' - ignored", op);
 196
 197       token = c_lex (&x);
 198       if (token != CPP_COMMA && action == push)
 199         GCC_BAD_ACTION;
 200
 201       if (token == CPP_COMMA)
 202         {
 203           token = c_lex (&x);
 204           if (token == CPP_NAME)
 205             {
 206               id = x;
 207               if (action == push && c_lex (&x) != CPP_COMMA)
 208                 GCC_BAD_ACTION;
 209               token = c_lex (&x);
 210             }
 211
 212           if (action == push)
 213             {
 214               if (token == CPP_NUMBER)
 215                 {
 216                   align = TREE_INT_CST_LOW (x);
 217                   token = c_lex (&x);
 218                 }
 219               else
 220                 GCC_BAD_ACTION;
 221             }
 222         }
 223
 224       if (token != CPP_CLOSE_PAREN)
 225         GCC_BAD_ACTION;
 226 #undef GCC_BAD_ACTION
 227     }
 228   else
 229     GCC_BAD ("malformed '#pragma pack' - ignored");
 230
 231   if (c_lex (&x) != CPP_EOF)
 232     warning ("junk at end of '#pragma pack'");
 233
 234   if (action != pop)
 235     switch (align)
 236       {
 237       case 0:
 238       case 1:
 239       case 2:
 240       case 4:
 241       case 8:
 242       case 16:
 243         align *= BITS_PER_UNIT;
 244         break;
 245       default:
 246         GCC_BAD2 ("alignment must be a small power of two, not %d", align);
 247       }
 248
 249   switch (action)
 250     {
 251     case set:   SET_GLOBAL_ALIGNMENT (align);  break;
 252     case push:  push_alignment (align, id);    break;
 253     case pop:   pop_alignment (id);            break;
 254     }
 255 }
 256 #endif  /* HANDLE_PRAGMA_PACK */
 257
 258 static GTY(()) tree pending_weaks;
 259
 260 #ifdef HANDLE_PRAGMA_WEAK
 261 static void apply_pragma_weak (tree, tree);
 262 static void handle_pragma_weak (cpp_reader *);
 263
 264 static void
 265 apply_pragma_weak (tree decl, tree value)
 266 {
 267   if (value)
 268     {
 269       value = build_string (IDENTIFIER_LENGTH (value),
 270                             IDENTIFIER_POINTER (value));
 271       decl_attributes (&decl, build_tree_list (get_identifier ("alias"),
 272                                                build_tree_list (NULL, value)),
 273                        0);
 274     }
 275
 276   if (SUPPORTS_WEAK && DECL_EXTERNAL (decl) && TREE_USED (decl)
 277       && !DECL_WEAK (decl) /* Don't complain about a redundant #pragma.  */
 278       && TREE_SYMBOL_REFERENCED (DECL_ASSEMBLER_NAME (decl)))
 279     warning ("%Japplying #pragma weak '%D' after first use results "
 280              "in unspecified behavior", decl, decl);
 281
 282   declare_weak (decl);
 283 }
 284
 285 void
 286 maybe_apply_pragma_weak (tree decl)
 287 {
 288   tree *p, t, id;
 289
 290   /* Avoid asking for DECL_ASSEMBLER_NAME when it's not needed.  */
 291
 292   /* No weak symbols pending, take the short-cut.  */
 293   if (!pending_weaks)
 294     return;
 295   /* If it's not visible outside this file, it doesn't matter whether
 296      it's weak.  */
 297   if (!DECL_EXTERNAL (decl) && !TREE_PUBLIC (decl))
 298     return;
 299   /* If it's not a function or a variable, it can't be weak.
 300      FIXME: what kinds of things are visible outside this file but
 301      aren't functions or variables?   Should this be an abort() instead?  */
 302   if (TREE_CODE (decl) != FUNCTION_DECL && TREE_CODE (decl) != VAR_DECL)
 303     return;
 304
 305   id = DECL_ASSEMBLER_NAME (decl);
 306
 307   for (p = &pending_weaks; (t = *p) ; p = &TREE_CHAIN (t))
 308     if (id == TREE_PURPOSE (t))
 309       {
 310         apply_pragma_weak (decl, TREE_VALUE (t));
 311         *p = TREE_CHAIN (t);
 312         break;
 313       }
 314 }
 315
 316 /* #pragma weak name [= value] */
 317 static void
 318 handle_pragma_weak (cpp_reader *dummy ATTRIBUTE_UNUSED)
 319 {
 320   tree name, value, x, decl;
 321   enum cpp_ttype t;
 322
 323   value = 0;
 324
 325   if (c_lex (&name) != CPP_NAME)
 326     GCC_BAD ("malformed #pragma weak, ignored");
 327   t = c_lex (&x);
 328   if (t == CPP_EQ)
 329     {
 330       if (c_lex (&value) != CPP_NAME)
 331         GCC_BAD ("malformed #pragma weak, ignored");
 332       t = c_lex (&x);
 333     }
 334   if (t != CPP_EOF)
 335     warning ("junk at end of #pragma weak");
 336
 337   decl = identifier_global_value (name);
 338   if (decl && TREE_CODE_CLASS (TREE_CODE (decl)) == 'd')
 339     {
 340       apply_pragma_weak (decl, value);
 341       if (value)
 342         assemble_alias (decl, value);
 343     }
 344   else
 345     pending_weaks = tree_cons (name, value, pending_weaks);
 346 }
 347 #else
 348 void
 349 maybe_apply_pragma_weak (tree decl ATTRIBUTE_UNUSED)
 350 {
 351 }
 352 #endif /* HANDLE_PRAGMA_WEAK */
 353
 354 /* GCC supports two #pragma directives for renaming the external
 355    symbol associated with a declaration (DECL_ASSEMBLER_NAME), for
 356    compatibility with the Solaris and Tru64 system headers.  GCC also
 357    has its own notation for this, __asm__("name") annotations.
 358
 359    Corner cases of these features and their interaction:
 360
 361    1) Both pragmas silently apply only to declarations with external
 362       linkage (that is, TREE_PUBLIC || DECL_EXTERNAL).  Asm labels
 363       do not have this restriction.
 364
 365    2) In C++, both #pragmas silently apply only to extern "C" declarations.
 366       Asm labels do not have this restriction.
 367
 368    3) If any of the three ways of changing DECL_ASSEMBLER_NAME is
 369       applied to a decl whose DECL_ASSEMBLER_NAME is already set, and the
 370       new name is different, a warning issues and the name does not change.
 371
 372    4) The "source name" for #pragma redefine_extname is the DECL_NAME,
 373       *not* the DECL_ASSEMBLER_NAME.
 374
 375    5) If #pragma extern_prefix is in effect and a declaration occurs
 376       with an __asm__ name, the #pragma extern_prefix is silently
 377       ignored for that declaration.
 378
 379    6) If #pragma extern_prefix and #pragma redefine_extname apply to
 380       the same declaration, whichever triggered first wins, and a warning
 381       is issued.  (We would like to have #pragma redefine_extname always
 382       win, but it can appear either before or after the declaration, and
 383       if it appears afterward, we have no way of knowing whether a modified
 384       DECL_ASSEMBLER_NAME is due to #pragma extern_prefix.)  */
 385
 386 static GTY(()) tree pending_redefine_extname;
 387
 388 static void handle_pragma_redefine_extname (cpp_reader *);
 389
 390 /* #pragma redefine_extname oldname newname */
 391 static void
 392 handle_pragma_redefine_extname (cpp_reader *dummy ATTRIBUTE_UNUSED)
 393 {
 394   tree oldname, newname, decl, x;
 395   enum cpp_ttype t;
 396
 397   if (c_lex (&oldname) != CPP_NAME)
 398     GCC_BAD ("malformed #pragma redefine_extname, ignored");
 399   if (c_lex (&newname) != CPP_NAME)
 400     GCC_BAD ("malformed #pragma redefine_extname, ignored");
 401   t = c_lex (&x);
 402   if (t != CPP_EOF)
 403     warning ("junk at end of #pragma redefine_extname");
 404
 405   if (!flag_mudflap && !targetm.handle_pragma_redefine_extname)
 406     {
 407       if (warn_unknown_pragmas > in_system_header)
 408         warning ("#pragma redefine_extname not supported on this target");
 409       return;
 410     }
 411
 412   decl = identifier_global_value (oldname);
 413   if (decl
 414       && (TREE_PUBLIC (decl) || DECL_EXTERNAL (decl))
 415       && (TREE_CODE (decl) == FUNCTION_DECL
 416           || TREE_CODE (decl) == VAR_DECL)
 417       && has_c_linkage (decl))
 418     {
 419       if (DECL_ASSEMBLER_NAME_SET_P (decl))
 420         {
 421           const char *name = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl));
 422           name = targetm.strip_name_encoding (name);
 423
 424           if (strcmp (name, IDENTIFIER_POINTER (newname)))
 425             warning ("#pragma redefine_extname ignored due to conflict with "
 426                      "previous rename");
 427         }
 428       else
 429         change_decl_assembler_name (decl, newname);
 430     }
 431   else
 432     /* We have to add this to the rename list even if there's already
 433        a global value that doesn't meet the above criteria, because in
 434        C++ "struct foo {...};" puts "foo" in the current namespace but
 435        does *not* conflict with a subsequent declaration of a function
 436        or variable foo.  See g++.dg/other/pragma-re-2.C.  */
 437     add_to_renaming_pragma_list (oldname, newname);
 438 }
 439
 440 /* This is called from here and from ia64.c.  */
 441 void
 442 add_to_renaming_pragma_list (tree oldname, tree newname)
 443 {
 444   tree previous = purpose_member (oldname, pending_redefine_extname);
 445   if (previous)
 446     {
 447       if (TREE_VALUE (previous) != newname)
 448         warning ("#pragma redefine_extname ignored due to conflict with "
 449                  "previous #pragma redefine_extname");
 450       return;
 451     }
 452
 453   pending_redefine_extname
 454     = tree_cons (oldname, newname, pending_redefine_extname);
 455 }
 456
 457 static GTY(()) tree pragma_extern_prefix;
 458
 459 /* #pragma extern_prefix "prefix" */
 460 static void
 461 handle_pragma_extern_prefix (cpp_reader *dummy ATTRIBUTE_UNUSED)
 462 {
 463   tree prefix, x;
 464   enum cpp_ttype t;
 465
 466   if (c_lex (&prefix) != CPP_STRING)
 467     GCC_BAD ("malformed #pragma extern_prefix, ignored");
 468   t = c_lex (&x);
 469   if (t != CPP_EOF)
 470     warning ("junk at end of #pragma extern_prefix");
 471
 472   if (targetm.handle_pragma_extern_prefix)
 473     /* Note that the length includes the null terminator.  */
 474     pragma_extern_prefix = (TREE_STRING_LENGTH (prefix) > 1 ? prefix : NULL);
 475   else if (warn_unknown_pragmas > in_system_header)
 476     warning ("#pragma extern_prefix not supported on this target");
 477 }
 478
 479 /* Hook from the front ends to apply the results of one of the preceding
 480    pragmas that rename variables.  */
 481
 482 tree
 483 maybe_apply_renaming_pragma (tree decl, tree asmname)
 484 {
 485   tree *p, t;
 486
 487   /* The renaming pragmas are only applied to declarations with
 488      external linkage.  */
 489   if ((TREE_CODE (decl) != FUNCTION_DECL && TREE_CODE (decl) != VAR_DECL)
 490       || (!TREE_PUBLIC (decl) && !DECL_EXTERNAL (decl))
 491       || !has_c_linkage (decl))
 492     return asmname;
 493
 494   /* If the DECL_ASSEMBLER_NAME is already set, it does not change,
 495      but we may warn about a rename that conflicts.  */
 496   if (DECL_ASSEMBLER_NAME_SET_P (decl))
 497     {
 498       const char *oldname = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl));
 499       oldname = targetm.strip_name_encoding (oldname);
 500
 501       if (asmname && strcmp (TREE_STRING_POINTER (asmname), oldname))
 502           warning ("asm declaration ignored due to "
 503                    "conflict with previous rename");
 504
 505       /* Take any pending redefine_extname off the list.  */
 506       for (p = &pending_redefine_extname; (t = *p); p = &TREE_CHAIN (t))
 507         if (DECL_NAME (decl) == TREE_PURPOSE (t))
 508           {
 509             /* Only warn if there is a conflict.  */
 510             if (strcmp (IDENTIFIER_POINTER (TREE_VALUE (t)), oldname))
 511               warning ("#pragma redefine_extname ignored due to "
 512                        "conflict with previous rename");
 513
 514             *p = TREE_CHAIN (t);
 515             break;
 516           }
 517       return 0;
 518     }
 519
 520   /* Find out if we have a pending #pragma redefine_extname.  */
 521   for (p = &pending_redefine_extname; (t = *p); p = &TREE_CHAIN (t))
 522     if (DECL_NAME (decl) == TREE_PURPOSE (t))
 523       {
 524         tree newname = TREE_VALUE (t);
 525         *p = TREE_CHAIN (t);
 526
 527         /* If we already have an asmname, #pragma redefine_extname is
 528            ignored (with a warning if it conflicts).  */
 529         if (asmname)
 530           {
 531             if (strcmp (TREE_STRING_POINTER (asmname),
 532                         IDENTIFIER_POINTER (newname)) != 0)
 533               warning ("#pragma redefine_extname ignored due to "
 534                        "conflict with __asm__ declaration");
 535             return asmname;
 536           }
 537
 538         /* Otherwise we use what we've got; #pragma extern_prefix is
 539            silently ignored.  */
 540         return build_string (IDENTIFIER_LENGTH (newname),
 541                              IDENTIFIER_POINTER (newname));
 542       }
 543
 544   /* If we've got an asmname, #pragma extern_prefix is silently ignored.  */
 545   if (asmname)
 546     return asmname;
 547
 548   /* If #pragma extern_prefix is in effect, apply it.  */
 549   if (pragma_extern_prefix)
 550     {
 551       const char *prefix = TREE_STRING_POINTER (pragma_extern_prefix);
 552       size_t plen = TREE_STRING_LENGTH (pragma_extern_prefix) - 1;
 553
 554       const char *id = IDENTIFIER_POINTER (DECL_NAME (decl));
 555       size_t ilen = IDENTIFIER_LENGTH (DECL_NAME (decl));
 556
 557       char *newname = alloca (plen + ilen + 1);
 558
 559       memcpy (newname,        prefix, plen);
 560       memcpy (newname + plen, id, ilen + 1);
 561
 562       return build_string (plen + ilen, newname);
 563     }
 564
 565   /* Nada.  */
 566   return 0;
 567 }
 568
 569 /* Front-end wrapper for pragma registration to avoid dragging
 570    cpplib.h in almost everywhere.  */
 571 void
 572 c_register_pragma (const char *space, const char *name,
 573                    void (*handler) (struct cpp_reader *))
 574 {
 575   cpp_register_pragma (parse_in, space, name, handler);
 576 }
 577
 578 /* Set up front-end pragmas.  */
 579 void
 580 init_pragma (void)
 581 {
 582 #ifdef HANDLE_PRAGMA_PACK
 583   c_register_pragma (0, "pack", handle_pragma_pack);
 584 #endif
 585 #ifdef HANDLE_PRAGMA_WEAK
 586   c_register_pragma (0, "weak", handle_pragma_weak);
 587 #endif
 588
 589   c_register_pragma (0, "redefine_extname", handle_pragma_redefine_extname);
 590   c_register_pragma (0, "extern_prefix", handle_pragma_extern_prefix);
 591
 592   c_register_pragma ("GCC", "pch_preprocess", c_common_pch_pragma);
 593
 594 #ifdef REGISTER_TARGET_PRAGMAS
 595   REGISTER_TARGET_PRAGMAS ();
 596 #endif
 597 }
 598
 599 #include "gt-c-pragma.h"