gas/frags.c

   1 /* frags.c - manage frags -
   2    Copyright 1987, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   3    1999, 2000, 2001, 2003, 2004, 2005, 2006, 2007
   4    Free Software Foundation, Inc.
   5
   6    This file is part of GAS, the GNU Assembler.
   7
   8    GAS is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3, or (at your option)
  11    any later version.
  12
  13    GAS is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with GAS; see the file COPYING.  If not, write to the Free
  20    Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
  21    02110-1301, USA.  */
  22
  23 #include "as.h"
  24 #include "subsegs.h"
  25 #include "obstack.h"
  26
  27 extern fragS zero_address_frag;
  28 extern fragS bss_address_frag;
  29 \f
  30 /* Initialization for frag routines.  */
  31
  32 void
  33 frag_init (void)
  34 {
  35   zero_address_frag.fr_type = rs_fill;
  36   bss_address_frag.fr_type = rs_fill;
  37 }
  38 \f
  39 /* Check that we're not trying to assemble into a section that can't
  40    allocate frags (currently, this is only possible in the absolute
  41    section), or into an mri common.  */
  42
  43 static void
  44 frag_alloc_check (const struct obstack *ob)
  45 {
  46   if (ob->chunk_size == 0)
  47     {
  48       as_bad (_("attempt to allocate data in absolute section"));
  49       subseg_set (text_section, 0);
  50     }
  51
  52   if (mri_common_symbol != NULL)
  53     {
  54       as_bad (_("attempt to allocate data in common section"));
  55       mri_common_symbol = NULL;
  56     }
  57 }
  58
  59 /* Allocate a frag on the specified obstack.
  60    Call this routine from everywhere else, so that all the weird alignment
  61    hackery can be done in just one place.  */
  62
  63 fragS *
  64 frag_alloc (struct obstack *ob)
  65 {
  66   fragS *ptr;
  67   int oalign;
  68
  69   (void) obstack_alloc (ob, 0);
  70   oalign = obstack_alignment_mask (ob);
  71   obstack_alignment_mask (ob) = 0;
  72   ptr = obstack_alloc (ob, SIZEOF_STRUCT_FRAG);
  73   obstack_alignment_mask (ob) = oalign;
  74   memset (ptr, 0, SIZEOF_STRUCT_FRAG);
  75   return ptr;
  76 }
  77 \f
  78 /* Try to augment current frag by nchars chars.
  79    If there is no room, close of the current frag with a ".fill 0"
  80    and begin a new frag. Unless the new frag has nchars chars available
  81    do not return. Do not set up any fields of *now_frag.  */
  82
  83 void
  84 frag_grow (unsigned int nchars)
  85 {
  86   if (obstack_room (&frchain_now->frch_obstack) < nchars)
  87     {
  88       unsigned int n;
  89       long oldc;
  90
  91       frag_wane (frag_now);
  92       frag_new (0);
  93       oldc = frchain_now->frch_obstack.chunk_size;
  94       /* Try to allocate a bit more than needed right now.  But don't do
  95          this if we would waste too much memory.  Especially necessary
  96          for extremely big (like 2GB initialized) frags.  */
  97       if (nchars < 0x10000)
  98         frchain_now->frch_obstack.chunk_size = 2 * nchars;
  99       else
 100         frchain_now->frch_obstack.chunk_size = nchars + 0x10000;
 101       frchain_now->frch_obstack.chunk_size += SIZEOF_STRUCT_FRAG;
 102       if (frchain_now->frch_obstack.chunk_size > 0)
 103         while ((n = obstack_room (&frchain_now->frch_obstack)) < nchars
 104                && (unsigned long) frchain_now->frch_obstack.chunk_size > nchars)
 105           {
 106             frag_wane (frag_now);
 107             frag_new (0);
 108           }
 109       frchain_now->frch_obstack.chunk_size = oldc;
 110     }
 111   if (obstack_room (&frchain_now->frch_obstack) < nchars)
 112     as_fatal (_("can't extend frag %u chars"), nchars);
 113 }
 114 \f
 115 /* Call this to close off a completed frag, and start up a new (empty)
 116    frag, in the same subsegment as the old frag.
 117    [frchain_now remains the same but frag_now is updated.]
 118    Because this calculates the correct value of fr_fix by
 119    looking at the obstack 'frags', it needs to know how many
 120    characters at the end of the old frag belong to the maximal
 121    variable part;  The rest must belong to fr_fix.
 122    It doesn't actually set up the old frag's fr_var.  You may have
 123    set fr_var == 1, but allocated 10 chars to the end of the frag;
 124    In this case you pass old_frags_var_max_size == 10.
 125    In fact, you may use fr_var for something totally unrelated to the
 126    size of the variable part of the frag;  None of the generic frag
 127    handling code makes use of fr_var.
 128
 129    Make a new frag, initialising some components. Link new frag at end
 130    of frchain_now.  */
 131
 132 void
 133 frag_new (int old_frags_var_max_size
 134           /* Number of chars (already allocated on obstack frags) in
 135              variable_length part of frag.  */)
 136 {
 137   fragS *former_last_fragP;
 138   frchainS *frchP;
 139
 140   gas_assert (frchain_now->frch_last == frag_now);
 141
 142   /* Fix up old frag's fr_fix.  */
 143   frag_now->fr_fix = frag_now_fix_octets () - old_frags_var_max_size;
 144   /* Make sure its type is valid.  */
 145   gas_assert (frag_now->fr_type != 0);
 146
 147   /* This will align the obstack so the next struct we allocate on it
 148      will begin at a correct boundary.  */
 149   obstack_finish (&frchain_now->frch_obstack);
 150   frchP = frchain_now;
 151   know (frchP);
 152   former_last_fragP = frchP->frch_last;
 153   gas_assert (former_last_fragP != 0);
 154   gas_assert (former_last_fragP == frag_now);
 155   frag_now = frag_alloc (&frchP->frch_obstack);
 156
 157   as_where (&frag_now->fr_file, &frag_now->fr_line);
 158
 159   /* Generally, frag_now->points to an address rounded up to next
 160      alignment.  However, characters will add to obstack frags
 161      IMMEDIATELY after the struct frag, even if they are not starting
 162      at an alignment address.  */
 163   former_last_fragP->fr_next = frag_now;
 164   frchP->frch_last = frag_now;
 165
 166 #ifndef NO_LISTING
 167   {
 168     extern struct list_info_struct *listing_tail;
 169     frag_now->line = listing_tail;
 170   }
 171 #endif
 172
 173   gas_assert (frchain_now->frch_last == frag_now);
 174
 175   frag_now->fr_next = NULL;
 176 }
 177 \f
 178 /* Start a new frag unless we have n more chars of room in the current frag.
 179    Close off the old frag with a .fill 0.
 180
 181    Return the address of the 1st char to write into. Advance
 182    frag_now_growth past the new chars.  */
 183
 184 char *
 185 frag_more (int nchars)
 186 {
 187   register char *retval;
 188
 189   frag_alloc_check (&frchain_now->frch_obstack);
 190   frag_grow (nchars);
 191   retval = obstack_next_free (&frchain_now->frch_obstack);
 192   obstack_blank_fast (&frchain_now->frch_obstack, nchars);
 193   return (retval);
 194 }
 195 \f
 196 /* Start a new frag unless we have max_chars more chars of room in the
 197    current frag.  Close off the old frag with a .fill 0.
 198
 199    Set up a machine_dependent relaxable frag, then start a new frag.
 200    Return the address of the 1st char of the var part of the old frag
 201    to write into.  */
 202
 203 char *
 204 frag_var (relax_stateT type, int max_chars, int var, relax_substateT subtype,
 205           symbolS *symbol, offsetT offset, char *opcode)
 206 {
 207   register char *retval;
 208
 209   frag_grow (max_chars);
 210   retval = obstack_next_free (&frchain_now->frch_obstack);
 211   obstack_blank_fast (&frchain_now->frch_obstack, max_chars);
 212   frag_now->fr_var = var;
 213   frag_now->fr_type = type;
 214   frag_now->fr_subtype = subtype;
 215   frag_now->fr_symbol = symbol;
 216   frag_now->fr_offset = offset;
 217   frag_now->fr_opcode = opcode;
 218 #ifdef USING_CGEN
 219   frag_now->fr_cgen.insn = 0;
 220   frag_now->fr_cgen.opindex = 0;
 221   frag_now->fr_cgen.opinfo = 0;
 222 #endif
 223 #ifdef TC_FRAG_INIT
 224   TC_FRAG_INIT (frag_now);
 225 #endif
 226   as_where (&frag_now->fr_file, &frag_now->fr_line);
 227   frag_new (max_chars);
 228   return (retval);
 229 }
 230 \f
 231 /* OVE: This variant of frag_var assumes that space for the tail has been
 232         allocated by caller.
 233         No call to frag_grow is done.  */
 234
 235 char *
 236 frag_variant (relax_stateT type, int max_chars, int var,
 237               relax_substateT subtype, symbolS *symbol, offsetT offset,
 238               char *opcode)
 239 {
 240   register char *retval;
 241
 242   retval = obstack_next_free (&frchain_now->frch_obstack);
 243   frag_now->fr_var = var;
 244   frag_now->fr_type = type;
 245   frag_now->fr_subtype = subtype;
 246   frag_now->fr_symbol = symbol;
 247   frag_now->fr_offset = offset;
 248   frag_now->fr_opcode = opcode;
 249 #ifdef USING_CGEN
 250   frag_now->fr_cgen.insn = 0;
 251   frag_now->fr_cgen.opindex = 0;
 252   frag_now->fr_cgen.opinfo = 0;
 253 #endif
 254 #ifdef TC_FRAG_INIT
 255   TC_FRAG_INIT (frag_now);
 256 #endif
 257   as_where (&frag_now->fr_file, &frag_now->fr_line);
 258   frag_new (max_chars);
 259   return (retval);
 260 }
 261 \f
 262 /* Reduce the variable end of a frag to a harmless state.  */
 263
 264 void
 265 frag_wane (register fragS *fragP)
 266 {
 267   fragP->fr_type = rs_fill;
 268   fragP->fr_offset = 0;
 269   fragP->fr_var = 0;
 270 }
 271 \f
 272 /* Return the number of bytes by which the current frag can be grown.  */
 273
 274 int
 275 frag_room (void)
 276 {
 277   return obstack_room (&frchain_now->frch_obstack);
 278 }
 279 \f
 280 /* Make an alignment frag.  The size of this frag will be adjusted to
 281    force the next frag to have the appropriate alignment.  ALIGNMENT
 282    is the power of two to which to align.  FILL_CHARACTER is the
 283    character to use to fill in any bytes which are skipped.  MAX is
 284    the maximum number of characters to skip when doing the alignment,
 285    or 0 if there is no maximum.  */
 286
 287 void
 288 frag_align (int alignment, int fill_character, int max)
 289 {
 290   if (now_seg == absolute_section)
 291     {
 292       addressT new_off;
 293       addressT mask;
 294
 295       mask = (~(addressT) 0) << alignment;
 296       new_off = (abs_section_offset + ~mask) & mask;
 297       if (max == 0 || new_off - abs_section_offset <= (addressT) max)
 298         abs_section_offset = new_off;
 299     }
 300   else
 301     {
 302       char *p;
 303
 304       p = frag_var (rs_align, 1, 1, (relax_substateT) max,
 305                     (symbolS *) 0, (offsetT) alignment, (char *) 0);
 306       *p = fill_character;
 307     }
 308 }
 309
 310 /* Make an alignment frag like frag_align, but fill with a repeating
 311    pattern rather than a single byte.  ALIGNMENT is the power of two
 312    to which to align.  FILL_PATTERN is the fill pattern to repeat in
 313    the bytes which are skipped.  N_FILL is the number of bytes in
 314    FILL_PATTERN.  MAX is the maximum number of characters to skip when
 315    doing the alignment, or 0 if there is no maximum.  */
 316
 317 void
 318 frag_align_pattern (int alignment, const char *fill_pattern,
 319                     int n_fill, int max)
 320 {
 321   char *p;
 322
 323   p = frag_var (rs_align, n_fill, n_fill, (relax_substateT) max,
 324                 (symbolS *) 0, (offsetT) alignment, (char *) 0);
 325   memcpy (p, fill_pattern, n_fill);
 326 }
 327
 328 /* The NOP_OPCODE is for the alignment fill value.  Fill it with a nop
 329    instruction so that the disassembler does not choke on it.  */
 330 #ifndef NOP_OPCODE
 331 #define NOP_OPCODE 0x00
 332 #endif
 333
 334 /* Use this to restrict the amount of memory allocated for representing
 335    the alignment code.  Needs to be large enough to hold any fixed sized
 336    prologue plus the replicating portion.  */
 337 #ifndef MAX_MEM_FOR_RS_ALIGN_CODE
 338   /* Assume that if HANDLE_ALIGN is not defined then no special action
 339      is required to code fill, which means that we get just repeat the
 340      one NOP_OPCODE byte.  */
 341 # ifndef HANDLE_ALIGN
 342 #  define MAX_MEM_FOR_RS_ALIGN_CODE  1
 343 # else
 344 #  define MAX_MEM_FOR_RS_ALIGN_CODE  ((1 << alignment) - 1)
 345 # endif
 346 #endif
 347
 348 void
 349 frag_align_code (int alignment, int max)
 350 {
 351   char *p;
 352
 353   p = frag_var (rs_align_code, MAX_MEM_FOR_RS_ALIGN_CODE, 1,
 354                 (relax_substateT) max, (symbolS *) 0,
 355                 (offsetT) alignment, (char *) 0);
 356   *p = NOP_OPCODE;
 357 }
 358
 359 addressT
 360 frag_now_fix_octets (void)
 361 {
 362   if (now_seg == absolute_section)
 363     return abs_section_offset;
 364
 365   return ((char *) obstack_next_free (&frchain_now->frch_obstack)
 366           - frag_now->fr_literal);
 367 }
 368
 369 addressT
 370 frag_now_fix (void)
 371 {
 372   return frag_now_fix_octets () / OCTETS_PER_BYTE;
 373 }
 374
 375 void
 376 frag_append_1_char (int datum)
 377 {
 378   frag_alloc_check (&frchain_now->frch_obstack);
 379   if (obstack_room (&frchain_now->frch_obstack) <= 1)
 380     {
 381       frag_wane (frag_now);
 382       frag_new (0);
 383     }
 384   obstack_1grow (&frchain_now->frch_obstack, datum);
 385 }
 386
 387 /* Return TRUE if FRAG1 and FRAG2 have a fixed relationship between
 388    their start addresses.  Set OFFSET to the difference in address
 389    not already accounted for in the frag FR_ADDRESS.  */
 390
 391 bfd_boolean
 392 frag_offset_fixed_p (const fragS *frag1, const fragS *frag2, bfd_vma *offset)
 393 {
 394   const fragS *frag;
 395   bfd_vma off;
 396
 397   /* Start with offset initialised to difference between the two frags.
 398      Prior to assigning frag addresses this will be zero.  */
 399   off = frag1->fr_address - frag2->fr_address;
 400   if (frag1 == frag2)
 401     {
 402       *offset = off;
 403       return TRUE;
 404     }
 405
 406   /* Maybe frag2 is after frag1.  */
 407   frag = frag1;
 408   while (frag->fr_type == rs_fill)
 409     {
 410       off += frag->fr_fix + frag->fr_offset * frag->fr_var;
 411       frag = frag->fr_next;
 412       if (frag == NULL)
 413         break;
 414       if (frag == frag2)
 415         {
 416           *offset = off;
 417           return TRUE;
 418         }
 419     }
 420
 421   /* Maybe frag1 is after frag2.  */
 422   off = frag1->fr_address - frag2->fr_address;
 423   frag = frag2;
 424   while (frag->fr_type == rs_fill)
 425     {
 426       off -= frag->fr_fix + frag->fr_offset * frag->fr_var;
 427       frag = frag->fr_next;
 428       if (frag == NULL)
 429         break;
 430       if (frag == frag1)
 431         {
 432           *offset = off;
 433           return TRUE;
 434         }
 435     }
 436
 437   return FALSE;
 438 }