gas/frags.c

   1 /* frags.c - manage frags -
   2    Copyright (C) 1987-2014 Free Software Foundation, Inc.
   3
   4    This file is part of GAS, the GNU Assembler.
   5
   6    GAS is free software; you can redistribute it and/or modify
   7    it 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    GAS is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with GAS; see the file COPYING.  If not, write to the Free
  18    Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
  19    02110-1301, USA.  */
  20
  21 #include "as.h"
  22 #include "subsegs.h"
  23 #include "obstack.h"
  24
  25 extern fragS zero_address_frag;
  26 extern fragS predefined_address_frag;
  27
  28 static int totalfrags;
  29
  30 int
  31 get_frag_count (void)
  32 {
  33   return totalfrags;
  34 }
  35
  36 void
  37 clear_frag_count (void)
  38 {
  39   totalfrags = 0;
  40 }
  41 \f
  42 /* Initialization for frag routines.  */
  43
  44 void
  45 frag_init (void)
  46 {
  47   zero_address_frag.fr_type = rs_fill;
  48   predefined_address_frag.fr_type = rs_fill;
  49 }
  50 \f
  51 /* Check that we're not trying to assemble into a section that can't
  52    allocate frags (currently, this is only possible in the absolute
  53    section), or into an mri common.  */
  54
  55 static void
  56 frag_alloc_check (const struct obstack *ob)
  57 {
  58   if (ob->chunk_size == 0)
  59     {
  60       as_bad (_("attempt to allocate data in absolute section"));
  61       subseg_set (text_section, 0);
  62     }
  63
  64   if (mri_common_symbol != NULL)
  65     {
  66       as_bad (_("attempt to allocate data in common section"));
  67       mri_common_symbol = NULL;
  68     }
  69 }
  70
  71 /* Allocate a frag on the specified obstack.
  72    Call this routine from everywhere else, so that all the weird alignment
  73    hackery can be done in just one place.  */
  74
  75 fragS *
  76 frag_alloc (struct obstack *ob)
  77 {
  78   fragS *ptr;
  79   int oalign;
  80
  81   (void) obstack_alloc (ob, 0);
  82   oalign = obstack_alignment_mask (ob);
  83   obstack_alignment_mask (ob) = 0;
  84   ptr = (fragS *) obstack_alloc (ob, SIZEOF_STRUCT_FRAG);
  85   obstack_alignment_mask (ob) = oalign;
  86   memset (ptr, 0, SIZEOF_STRUCT_FRAG);
  87   totalfrags++;
  88   return ptr;
  89 }
  90 \f
  91 /* Try to augment current frag by nchars chars.
  92    If there is no room, close of the current frag with a ".fill 0"
  93    and begin a new frag. Unless the new frag has nchars chars available
  94    do not return. Do not set up any fields of *now_frag.  */
  95
  96 void
  97 frag_grow (unsigned int nchars)
  98 {
  99   if (obstack_room (&frchain_now->frch_obstack) < nchars)
 100     {
 101       long oldc;
 102       long newc;
 103
 104       /* Try to allocate a bit more than needed right now.  But don't do
 105          this if we would waste too much memory.  Especially necessary
 106          for extremely big (like 2GB initialized) frags.  */
 107       if (nchars < 0x10000)
 108         newc = 2 * nchars;
 109       else
 110         newc = nchars + 0x10000;
 111       newc += SIZEOF_STRUCT_FRAG;
 112
 113       /* Check for possible overflow.  */
 114       if (newc < 0)
 115         as_fatal (_("can't extend frag %u chars"), nchars);
 116
 117       /* Force to allocate at least NEWC bytes, but not less than the
 118          default.  */
 119       oldc = obstack_chunk_size (&frchain_now->frch_obstack);
 120       if (newc > oldc)
 121         obstack_chunk_size (&frchain_now->frch_obstack) = newc;
 122
 123       while (obstack_room (&frchain_now->frch_obstack) < nchars)
 124         {
 125           /* Not enough room in this frag.  Close it and start a new one.
 126              This must be done in a loop because the created frag may not
 127              be big enough if the current obstack chunk is used.  */
 128           frag_wane (frag_now);
 129           frag_new (0);
 130         }
 131
 132       /* Restore the old chunk size.  */
 133       obstack_chunk_size (&frchain_now->frch_obstack) = oldc;
 134     }
 135 }
 136 \f
 137 /* Call this to close off a completed frag, and start up a new (empty)
 138    frag, in the same subsegment as the old frag.
 139    [frchain_now remains the same but frag_now is updated.]
 140    Because this calculates the correct value of fr_fix by
 141    looking at the obstack 'frags', it needs to know how many
 142    characters at the end of the old frag belong to the maximal
 143    variable part;  The rest must belong to fr_fix.
 144    It doesn't actually set up the old frag's fr_var.  You may have
 145    set fr_var == 1, but allocated 10 chars to the end of the frag;
 146    In this case you pass old_frags_var_max_size == 10.
 147    In fact, you may use fr_var for something totally unrelated to the
 148    size of the variable part of the frag;  None of the generic frag
 149    handling code makes use of fr_var.
 150
 151    Make a new frag, initialising some components. Link new frag at end
 152    of frchain_now.  */
 153
 154 void
 155 frag_new (int old_frags_var_max_size
 156           /* Number of chars (already allocated on obstack frags) in
 157              variable_length part of frag.  */)
 158 {
 159   fragS *former_last_fragP;
 160   frchainS *frchP;
 161
 162   gas_assert (frchain_now->frch_last == frag_now);
 163
 164   /* Fix up old frag's fr_fix.  */
 165   frag_now->fr_fix = frag_now_fix_octets () - old_frags_var_max_size;
 166   /* Make sure its type is valid.  */
 167   gas_assert (frag_now->fr_type != 0);
 168
 169   /* This will align the obstack so the next struct we allocate on it
 170      will begin at a correct boundary.  */
 171   obstack_finish (&frchain_now->frch_obstack);
 172   frchP = frchain_now;
 173   know (frchP);
 174   former_last_fragP = frchP->frch_last;
 175   gas_assert (former_last_fragP != 0);
 176   gas_assert (former_last_fragP == frag_now);
 177   frag_now = frag_alloc (&frchP->frch_obstack);
 178
 179   as_where (&frag_now->fr_file, &frag_now->fr_line);
 180
 181   /* Generally, frag_now->points to an address rounded up to next
 182      alignment.  However, characters will add to obstack frags
 183      IMMEDIATELY after the struct frag, even if they are not starting
 184      at an alignment address.  */
 185   former_last_fragP->fr_next = frag_now;
 186   frchP->frch_last = frag_now;
 187
 188 #ifndef NO_LISTING
 189   {
 190     extern struct list_info_struct *listing_tail;
 191     frag_now->line = listing_tail;
 192   }
 193 #endif
 194
 195   gas_assert (frchain_now->frch_last == frag_now);
 196
 197   frag_now->fr_next = NULL;
 198 }
 199 \f
 200 /* Start a new frag unless we have n more chars of room in the current frag.
 201    Close off the old frag with a .fill 0.
 202
 203    Return the address of the 1st char to write into. Advance
 204    frag_now_growth past the new chars.  */
 205
 206 char *
 207 frag_more (int nchars)
 208 {
 209   register char *retval;
 210
 211   frag_alloc_check (&frchain_now->frch_obstack);
 212   frag_grow (nchars);
 213   retval = obstack_next_free (&frchain_now->frch_obstack);
 214   obstack_blank_fast (&frchain_now->frch_obstack, nchars);
 215   return (retval);
 216 }
 217 \f
 218 /* Close the current frag, setting its fields for a relaxable frag.  Start a
 219    new frag.  */
 220
 221 static void
 222 frag_var_init (relax_stateT type, int max_chars, int var,
 223                relax_substateT subtype, symbolS *symbol, offsetT offset,
 224                char *opcode)
 225 {
 226   frag_now->fr_var = var;
 227   frag_now->fr_type = type;
 228   frag_now->fr_subtype = subtype;
 229   frag_now->fr_symbol = symbol;
 230   frag_now->fr_offset = offset;
 231   frag_now->fr_opcode = opcode;
 232 #ifdef USING_CGEN
 233   frag_now->fr_cgen.insn = 0;
 234   frag_now->fr_cgen.opindex = 0;
 235   frag_now->fr_cgen.opinfo = 0;
 236 #endif
 237 #ifdef TC_FRAG_INIT
 238   TC_FRAG_INIT (frag_now);
 239 #endif
 240   as_where (&frag_now->fr_file, &frag_now->fr_line);
 241
 242   frag_new (max_chars);
 243 }
 244
 245 /* Start a new frag unless we have max_chars more chars of room in the
 246    current frag.  Close off the old frag with a .fill 0.
 247
 248    Set up a machine_dependent relaxable frag, then start a new frag.
 249    Return the address of the 1st char of the var part of the old frag
 250    to write into.  */
 251
 252 char *
 253 frag_var (relax_stateT type, int max_chars, int var, relax_substateT subtype,
 254           symbolS *symbol, offsetT offset, char *opcode)
 255 {
 256   register char *retval;
 257
 258   frag_grow (max_chars);
 259   retval = obstack_next_free (&frchain_now->frch_obstack);
 260   obstack_blank_fast (&frchain_now->frch_obstack, max_chars);
 261   frag_var_init (type, max_chars, var, subtype, symbol, offset, opcode);
 262   return retval;
 263 }
 264 \f
 265 /* OVE: This variant of frag_var assumes that space for the tail has been
 266         allocated by caller.
 267         No call to frag_grow is done.  */
 268
 269 char *
 270 frag_variant (relax_stateT type, int max_chars, int var,
 271               relax_substateT subtype, symbolS *symbol, offsetT offset,
 272               char *opcode)
 273 {
 274   register char *retval;
 275
 276   retval = obstack_next_free (&frchain_now->frch_obstack);
 277   frag_var_init (type, max_chars, var, subtype, symbol, offset, opcode);
 278
 279   return retval;
 280 }
 281 \f
 282 /* Reduce the variable end of a frag to a harmless state.  */
 283
 284 void
 285 frag_wane (register fragS *fragP)
 286 {
 287   fragP->fr_type = rs_fill;
 288   fragP->fr_offset = 0;
 289   fragP->fr_var = 0;
 290 }
 291 \f
 292 /* Return the number of bytes by which the current frag can be grown.  */
 293
 294 int
 295 frag_room (void)
 296 {
 297   return obstack_room (&frchain_now->frch_obstack);
 298 }
 299 \f
 300 /* Make an alignment frag.  The size of this frag will be adjusted to
 301    force the next frag to have the appropriate alignment.  ALIGNMENT
 302    is the power of two to which to align.  FILL_CHARACTER is the
 303    character to use to fill in any bytes which are skipped.  MAX is
 304    the maximum number of characters to skip when doing the alignment,
 305    or 0 if there is no maximum.  */
 306
 307 void
 308 frag_align (int alignment, int fill_character, int max)
 309 {
 310   if (now_seg == absolute_section)
 311     {
 312       addressT new_off;
 313       addressT mask;
 314
 315       mask = (~(addressT) 0) << alignment;
 316       new_off = (abs_section_offset + ~mask) & mask;
 317       if (max == 0 || new_off - abs_section_offset <= (addressT) max)
 318         abs_section_offset = new_off;
 319     }
 320   else
 321     {
 322       char *p;
 323
 324       p = frag_var (rs_align, 1, 1, (relax_substateT) max,
 325                     (symbolS *) 0, (offsetT) alignment, (char *) 0);
 326       *p = fill_character;
 327     }
 328 }
 329
 330 /* Make an alignment frag like frag_align, but fill with a repeating
 331    pattern rather than a single byte.  ALIGNMENT is the power of two
 332    to which to align.  FILL_PATTERN is the fill pattern to repeat in
 333    the bytes which are skipped.  N_FILL is the number of bytes in
 334    FILL_PATTERN.  MAX is the maximum number of characters to skip when
 335    doing the alignment, or 0 if there is no maximum.  */
 336
 337 void
 338 frag_align_pattern (int alignment, const char *fill_pattern,
 339                     int n_fill, int max)
 340 {
 341   char *p;
 342
 343   p = frag_var (rs_align, n_fill, n_fill, (relax_substateT) max,
 344                 (symbolS *) 0, (offsetT) alignment, (char *) 0);
 345   memcpy (p, fill_pattern, n_fill);
 346 }
 347
 348 /* The NOP_OPCODE is for the alignment fill value.  Fill it with a nop
 349    instruction so that the disassembler does not choke on it.  */
 350 #ifndef NOP_OPCODE
 351 #define NOP_OPCODE 0x00
 352 #endif
 353
 354 /* Use this to restrict the amount of memory allocated for representing
 355    the alignment code.  Needs to be large enough to hold any fixed sized
 356    prologue plus the replicating portion.  */
 357 #ifndef MAX_MEM_FOR_RS_ALIGN_CODE
 358   /* Assume that if HANDLE_ALIGN is not defined then no special action
 359      is required to code fill, which means that we get just repeat the
 360      one NOP_OPCODE byte.  */
 361 # ifndef HANDLE_ALIGN
 362 #  define MAX_MEM_FOR_RS_ALIGN_CODE  1
 363 # else
 364 #  define MAX_MEM_FOR_RS_ALIGN_CODE  ((1 << alignment) - 1)
 365 # endif
 366 #endif
 367
 368 void
 369 frag_align_code (int alignment, int max)
 370 {
 371   char *p;
 372
 373   p = frag_var (rs_align_code, MAX_MEM_FOR_RS_ALIGN_CODE, 1,
 374                 (relax_substateT) max, (symbolS *) 0,
 375                 (offsetT) alignment, (char *) 0);
 376   *p = NOP_OPCODE;
 377 }
 378
 379 addressT
 380 frag_now_fix_octets (void)
 381 {
 382   if (now_seg == absolute_section)
 383     return abs_section_offset;
 384
 385   return ((char *) obstack_next_free (&frchain_now->frch_obstack)
 386           - frag_now->fr_literal);
 387 }
 388
 389 addressT
 390 frag_now_fix (void)
 391 {
 392   return frag_now_fix_octets () / OCTETS_PER_BYTE;
 393 }
 394
 395 void
 396 frag_append_1_char (int datum)
 397 {
 398   frag_alloc_check (&frchain_now->frch_obstack);
 399   if (obstack_room (&frchain_now->frch_obstack) <= 1)
 400     {
 401       frag_wane (frag_now);
 402       frag_new (0);
 403     }
 404   obstack_1grow (&frchain_now->frch_obstack, datum);
 405 }
 406
 407 /* Return TRUE if FRAG1 and FRAG2 have a fixed relationship between
 408    their start addresses.  Set OFFSET to the difference in address
 409    not already accounted for in the frag FR_ADDRESS.  */
 410
 411 bfd_boolean
 412 frag_offset_fixed_p (const fragS *frag1, const fragS *frag2, offsetT *offset)
 413 {
 414   const fragS *frag;
 415   offsetT off;
 416
 417   /* Start with offset initialised to difference between the two frags.
 418      Prior to assigning frag addresses this will be zero.  */
 419   off = frag1->fr_address - frag2->fr_address;
 420   if (frag1 == frag2)
 421     {
 422       *offset = off;
 423       return TRUE;
 424     }
 425
 426   /* Maybe frag2 is after frag1.  */
 427   frag = frag1;
 428   while (frag->fr_type == rs_fill)
 429     {
 430       off += frag->fr_fix + frag->fr_offset * frag->fr_var;
 431       frag = frag->fr_next;
 432       if (frag == NULL)
 433         break;
 434       if (frag == frag2)
 435         {
 436           *offset = off;
 437           return TRUE;
 438         }
 439     }
 440
 441   /* Maybe frag1 is after frag2.  */
 442   off = frag1->fr_address - frag2->fr_address;
 443   frag = frag2;
 444   while (frag->fr_type == rs_fill)
 445     {
 446       off -= frag->fr_fix + frag->fr_offset * frag->fr_var;
 447       frag = frag->fr_next;
 448       if (frag == NULL)
 449         break;
 450       if (frag == frag1)
 451         {
 452           *offset = off;
 453           return TRUE;
 454         }
 455     }
 456
 457   return FALSE;
 458 }