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, 2008, 2009
   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 predefined_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   predefined_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 = (fragS *) 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       long oldc;
  89       long newc;
  90
  91       /* Try to allocate a bit more than needed right now.  But don't do
  92          this if we would waste too much memory.  Especially necessary
  93          for extremely big (like 2GB initialized) frags.  */
  94       if (nchars < 0x10000)
  95         newc = 2 * nchars;
  96       else
  97         newc = nchars + 0x10000;
  98       newc += SIZEOF_STRUCT_FRAG;
  99
 100       /* Check for possible overflow.  */
 101       if (newc < 0)
 102         as_fatal (_("can't extend frag %u chars"), nchars);
 103
 104       /* Force to allocate at least NEWC bytes.  */
 105       oldc = obstack_chunk_size (&frchain_now->frch_obstack);
 106       obstack_chunk_size (&frchain_now->frch_obstack) = newc;
 107
 108       while (obstack_room (&frchain_now->frch_obstack) < nchars)
 109         {
 110           /* Not enough room in this frag.  Close it and start a new one.
 111              This must be done in a loop because the created frag may not
 112              be big enough if the current obstack chunk is used.  */
 113           frag_wane (frag_now);
 114           frag_new (0);
 115         }
 116
 117       /* Restore the old chunk size.  */
 118       obstack_chunk_size (&frchain_now->frch_obstack) = oldc;
 119     }
 120 }
 121 \f
 122 /* Call this to close off a completed frag, and start up a new (empty)
 123    frag, in the same subsegment as the old frag.
 124    [frchain_now remains the same but frag_now is updated.]
 125    Because this calculates the correct value of fr_fix by
 126    looking at the obstack 'frags', it needs to know how many
 127    characters at the end of the old frag belong to the maximal
 128    variable part;  The rest must belong to fr_fix.
 129    It doesn't actually set up the old frag's fr_var.  You may have
 130    set fr_var == 1, but allocated 10 chars to the end of the frag;
 131    In this case you pass old_frags_var_max_size == 10.
 132    In fact, you may use fr_var for something totally unrelated to the
 133    size of the variable part of the frag;  None of the generic frag
 134    handling code makes use of fr_var.
 135
 136    Make a new frag, initialising some components. Link new frag at end
 137    of frchain_now.  */
 138
 139 void
 140 frag_new (int old_frags_var_max_size
 141           /* Number of chars (already allocated on obstack frags) in
 142              variable_length part of frag.  */)
 143 {
 144   fragS *former_last_fragP;
 145   frchainS *frchP;
 146
 147   gas_assert (frchain_now->frch_last == frag_now);
 148
 149   /* Fix up old frag's fr_fix.  */
 150   frag_now->fr_fix = frag_now_fix_octets () - old_frags_var_max_size;
 151   /* Make sure its type is valid.  */
 152   gas_assert (frag_now->fr_type != 0);
 153
 154   /* This will align the obstack so the next struct we allocate on it
 155      will begin at a correct boundary.  */
 156   obstack_finish (&frchain_now->frch_obstack);
 157   frchP = frchain_now;
 158   know (frchP);
 159   former_last_fragP = frchP->frch_last;
 160   gas_assert (former_last_fragP != 0);
 161   gas_assert (former_last_fragP == frag_now);
 162   frag_now = frag_alloc (&frchP->frch_obstack);
 163
 164   as_where (&frag_now->fr_file, &frag_now->fr_line);
 165
 166   /* Generally, frag_now->points to an address rounded up to next
 167      alignment.  However, characters will add to obstack frags
 168      IMMEDIATELY after the struct frag, even if they are not starting
 169      at an alignment address.  */
 170   former_last_fragP->fr_next = frag_now;
 171   frchP->frch_last = frag_now;
 172
 173 #ifndef NO_LISTING
 174   {
 175     extern struct list_info_struct *listing_tail;
 176     frag_now->line = listing_tail;
 177   }
 178 #endif
 179
 180   gas_assert (frchain_now->frch_last == frag_now);
 181
 182   frag_now->fr_next = NULL;
 183 }
 184 \f
 185 /* Start a new frag unless we have n more chars of room in the current frag.
 186    Close off the old frag with a .fill 0.
 187
 188    Return the address of the 1st char to write into. Advance
 189    frag_now_growth past the new chars.  */
 190
 191 char *
 192 frag_more (int nchars)
 193 {
 194   register char *retval;
 195
 196   frag_alloc_check (&frchain_now->frch_obstack);
 197   frag_grow (nchars);
 198   retval = obstack_next_free (&frchain_now->frch_obstack);
 199   obstack_blank_fast (&frchain_now->frch_obstack, nchars);
 200   return (retval);
 201 }
 202 \f
 203 /* Close the current frag, setting its fields for a relaxable frag.  Start a
 204    new frag.  */
 205
 206 static void
 207 frag_var_init (relax_stateT type, int max_chars, int var,
 208                relax_substateT subtype, symbolS *symbol, offsetT offset,
 209                char *opcode)
 210 {
 211   frag_now->fr_var = var;
 212   frag_now->fr_type = type;
 213   frag_now->fr_subtype = subtype;
 214   frag_now->fr_symbol = symbol;
 215   frag_now->fr_offset = offset;
 216   frag_now->fr_opcode = opcode;
 217 #ifdef USING_CGEN
 218   frag_now->fr_cgen.insn = 0;
 219   frag_now->fr_cgen.opindex = 0;
 220   frag_now->fr_cgen.opinfo = 0;
 221 #endif
 222 #ifdef TC_FRAG_INIT
 223   TC_FRAG_INIT (frag_now);
 224 #endif
 225   as_where (&frag_now->fr_file, &frag_now->fr_line);
 226
 227   frag_new (max_chars);
 228 }
 229
 230 /* Start a new frag unless we have max_chars more chars of room in the
 231    current frag.  Close off the old frag with a .fill 0.
 232
 233    Set up a machine_dependent relaxable frag, then start a new frag.
 234    Return the address of the 1st char of the var part of the old frag
 235    to write into.  */
 236
 237 char *
 238 frag_var (relax_stateT type, int max_chars, int var, relax_substateT subtype,
 239           symbolS *symbol, offsetT offset, char *opcode)
 240 {
 241   register char *retval;
 242
 243   frag_grow (max_chars);
 244   retval = obstack_next_free (&frchain_now->frch_obstack);
 245   obstack_blank_fast (&frchain_now->frch_obstack, max_chars);
 246   frag_var_init (type, max_chars, var, subtype, symbol, offset, opcode);
 247   return retval;
 248 }
 249 \f
 250 /* OVE: This variant of frag_var assumes that space for the tail has been
 251         allocated by caller.
 252         No call to frag_grow is done.  */
 253
 254 char *
 255 frag_variant (relax_stateT type, int max_chars, int var,
 256               relax_substateT subtype, symbolS *symbol, offsetT offset,
 257               char *opcode)
 258 {
 259   register char *retval;
 260
 261   retval = obstack_next_free (&frchain_now->frch_obstack);
 262   frag_var_init (type, max_chars, var, subtype, symbol, offset, opcode);
 263
 264   return retval;
 265 }
 266 \f
 267 /* Reduce the variable end of a frag to a harmless state.  */
 268
 269 void
 270 frag_wane (register fragS *fragP)
 271 {
 272   fragP->fr_type = rs_fill;
 273   fragP->fr_offset = 0;
 274   fragP->fr_var = 0;
 275 }
 276 \f
 277 /* Return the number of bytes by which the current frag can be grown.  */
 278
 279 int
 280 frag_room (void)
 281 {
 282   return obstack_room (&frchain_now->frch_obstack);
 283 }
 284 \f
 285 /* Make an alignment frag.  The size of this frag will be adjusted to
 286    force the next frag to have the appropriate alignment.  ALIGNMENT
 287    is the power of two to which to align.  FILL_CHARACTER is the
 288    character to use to fill in any bytes which are skipped.  MAX is
 289    the maximum number of characters to skip when doing the alignment,
 290    or 0 if there is no maximum.  */
 291
 292 void
 293 frag_align (int alignment, int fill_character, int max)
 294 {
 295   if (now_seg == absolute_section)
 296     {
 297       addressT new_off;
 298       addressT mask;
 299
 300       mask = (~(addressT) 0) << alignment;
 301       new_off = (abs_section_offset + ~mask) & mask;
 302       if (max == 0 || new_off - abs_section_offset <= (addressT) max)
 303         abs_section_offset = new_off;
 304     }
 305   else
 306     {
 307       char *p;
 308
 309       p = frag_var (rs_align, 1, 1, (relax_substateT) max,
 310                     (symbolS *) 0, (offsetT) alignment, (char *) 0);
 311       *p = fill_character;
 312     }
 313 }
 314
 315 /* Make an alignment frag like frag_align, but fill with a repeating
 316    pattern rather than a single byte.  ALIGNMENT is the power of two
 317    to which to align.  FILL_PATTERN is the fill pattern to repeat in
 318    the bytes which are skipped.  N_FILL is the number of bytes in
 319    FILL_PATTERN.  MAX is the maximum number of characters to skip when
 320    doing the alignment, or 0 if there is no maximum.  */
 321
 322 void
 323 frag_align_pattern (int alignment, const char *fill_pattern,
 324                     int n_fill, int max)
 325 {
 326   char *p;
 327
 328   p = frag_var (rs_align, n_fill, n_fill, (relax_substateT) max,
 329                 (symbolS *) 0, (offsetT) alignment, (char *) 0);
 330   memcpy (p, fill_pattern, n_fill);
 331 }
 332
 333 /* The NOP_OPCODE is for the alignment fill value.  Fill it with a nop
 334    instruction so that the disassembler does not choke on it.  */
 335 #ifndef NOP_OPCODE
 336 #define NOP_OPCODE 0x00
 337 #endif
 338
 339 /* Use this to restrict the amount of memory allocated for representing
 340    the alignment code.  Needs to be large enough to hold any fixed sized
 341    prologue plus the replicating portion.  */
 342 #ifndef MAX_MEM_FOR_RS_ALIGN_CODE
 343   /* Assume that if HANDLE_ALIGN is not defined then no special action
 344      is required to code fill, which means that we get just repeat the
 345      one NOP_OPCODE byte.  */
 346 # ifndef HANDLE_ALIGN
 347 #  define MAX_MEM_FOR_RS_ALIGN_CODE  1
 348 # else
 349 #  define MAX_MEM_FOR_RS_ALIGN_CODE  ((1 << alignment) - 1)
 350 # endif
 351 #endif
 352
 353 void
 354 frag_align_code (int alignment, int max)
 355 {
 356   char *p;
 357
 358   p = frag_var (rs_align_code, MAX_MEM_FOR_RS_ALIGN_CODE, 1,
 359                 (relax_substateT) max, (symbolS *) 0,
 360                 (offsetT) alignment, (char *) 0);
 361   *p = NOP_OPCODE;
 362 }
 363
 364 addressT
 365 frag_now_fix_octets (void)
 366 {
 367   if (now_seg == absolute_section)
 368     return abs_section_offset;
 369
 370   return ((char *) obstack_next_free (&frchain_now->frch_obstack)
 371           - frag_now->fr_literal);
 372 }
 373
 374 addressT
 375 frag_now_fix (void)
 376 {
 377   return frag_now_fix_octets () / OCTETS_PER_BYTE;
 378 }
 379
 380 void
 381 frag_append_1_char (int datum)
 382 {
 383   frag_alloc_check (&frchain_now->frch_obstack);
 384   if (obstack_room (&frchain_now->frch_obstack) <= 1)
 385     {
 386       frag_wane (frag_now);
 387       frag_new (0);
 388     }
 389   obstack_1grow (&frchain_now->frch_obstack, datum);
 390 }
 391
 392 /* Return TRUE if FRAG1 and FRAG2 have a fixed relationship between
 393    their start addresses.  Set OFFSET to the difference in address
 394    not already accounted for in the frag FR_ADDRESS.  */
 395
 396 bfd_boolean
 397 frag_offset_fixed_p (const fragS *frag1, const fragS *frag2, bfd_vma *offset)
 398 {
 399   const fragS *frag;
 400   bfd_vma off;
 401
 402   /* Start with offset initialised to difference between the two frags.
 403      Prior to assigning frag addresses this will be zero.  */
 404   off = frag1->fr_address - frag2->fr_address;
 405   if (frag1 == frag2)
 406     {
 407       *offset = off;
 408       return TRUE;
 409     }
 410
 411   /* Maybe frag2 is after frag1.  */
 412   frag = frag1;
 413   while (frag->fr_type == rs_fill)
 414     {
 415       off += frag->fr_fix + frag->fr_offset * frag->fr_var;
 416       frag = frag->fr_next;
 417       if (frag == NULL)
 418         break;
 419       if (frag == frag2)
 420         {
 421           *offset = off;
 422           return TRUE;
 423         }
 424     }
 425
 426   /* Maybe frag1 is after frag2.  */
 427   off = frag1->fr_address - frag2->fr_address;
 428   frag = frag2;
 429   while (frag->fr_type == rs_fill)
 430     {
 431       off -= frag->fr_fix + frag->fr_offset * frag->fr_var;
 432       frag = frag->fr_next;
 433       if (frag == NULL)
 434         break;
 435       if (frag == frag1)
 436         {
 437           *offset = off;
 438           return TRUE;
 439         }
 440     }
 441
 442   return FALSE;
 443 }