gdb/dcache.c

   1 /* Caching code.  Typically used by remote back ends for
   2    caching remote memory.
   3
   4    Copyright 1992, 1993, 1995 Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program 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 2 of the License, or
  11    (at your option) any later version.
  12
  13    This program 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 this program; if not, write to the Free Software
  20    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  21
  22 #include "defs.h"
  23 #include "dcache.h"
  24 #include "gdbcmd.h"
  25 #include "gdb_string.h"
  26
  27
  28 /*
  29    The data cache could lead to incorrect results because it doesn't know
  30    about volatile variables, thus making it impossible to debug
  31    functions which use memory mapped I/O devices.
  32
  33    set remotecache 0
  34
  35    In those cases.
  36
  37    In general the dcache speeds up performance, some speed improvement
  38    comes from the actual caching mechanism, but the major gain is in
  39    the reduction of the remote protocol overhead; instead of reading
  40    or writing a large area of memory in 4 byte requests, the cache
  41    bundles up the requests into 32 byte (actually LINE_SIZE) chunks.
  42    Reducing the overhead to an eighth of what it was.  This is very
  43    obvious when displaying a large amount of data,
  44
  45    eg, x/200x 0
  46
  47    caching     |   no    yes
  48    ----------------------------
  49    first time  |   4 sec  2 sec improvement due to chunking
  50    second time |   4 sec  0 sec improvement due to caching
  51
  52    The cache structure is unusual, we keep a number of cache blocks
  53    (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
  54    Within each line we remember the address of the line (always a
  55    multiple of the LINE_SIZE) and a vector of bytes over the range.
  56    There's another vector which contains the state of the bytes.
  57
  58    ENTRY_BAD means that the byte is just plain wrong, and has no
  59    correspondence with anything else (as it would when the cache is
  60    turned on, but nothing has been done to it.
  61
  62    ENTRY_DIRTY means that the byte has some data in it which should be
  63    written out to the remote target one day, but contains correct
  64    data.  ENTRY_OK means that the data is the same in the cache as it
  65    is in remote memory.
  66
  67
  68    The ENTRY_DIRTY state is necessary because GDB likes to write large
  69    lumps of memory in small bits.  If the caching mechanism didn't
  70    maintain the DIRTY information, then something like a two byte
  71    write would mean that the entire cache line would have to be read,
  72    the two bytes modified and then written out again.  The alternative
  73    would be to not read in the cache line in the first place, and just
  74    write the two bytes directly into target memory.  The trouble with
  75    that is that it really nails performance, because of the remote
  76    protocol overhead.  This way, all those little writes are bundled
  77    up into an entire cache line write in one go, without having to
  78    read the cache line in the first place.
  79
  80
  81   */
  82
  83
  84 /* This value regulates the number of cache blocks stored.
  85    Smaller values reduce the time spent searching for a cache
  86    line, and reduce memory requirements, but increase the risk
  87    of a line not being in memory */
  88
  89 #define DCACHE_SIZE 64
  90
  91 /* This value regulates the size of a cache line.  Smaller values
  92    reduce the time taken to read a single byte, but reduce overall
  93    throughput.  */
  94
  95 #define LINE_SIZE_POWER (5)
  96 #define LINE_SIZE (1 << LINE_SIZE_POWER)
  97
  98 /* Each cache block holds LINE_SIZE bytes of data
  99    starting at a multiple-of-LINE_SIZE address.  */
 100
 101 #define LINE_SIZE_MASK  ((LINE_SIZE - 1))
 102 #define XFORM(x)        ((x) & LINE_SIZE_MASK)
 103 #define MASK(x)         ((x) & ~LINE_SIZE_MASK)
 104
 105
 106 #define ENTRY_BAD   0  /* data at this byte is wrong */
 107 #define ENTRY_DIRTY 1  /* data at this byte needs to be written back */
 108 #define ENTRY_OK    2  /* data at this byte is same as in memory */
 109
 110
 111 struct dcache_block
 112 {
 113   struct dcache_block *p;       /* next in list */
 114   unsigned int addr;            /* Address for which data is recorded.  */
 115   char data[LINE_SIZE];         /* bytes at given address */
 116   unsigned char state[LINE_SIZE]; /* what state the data is in */
 117
 118   /* whether anything in state is dirty - used to speed up the
 119      dirty scan. */
 120   int anydirty;
 121
 122   int refs;
 123 };
 124
 125
 126 struct dcache_struct
 127 {
 128   /* Function to actually read the target memory. */
 129   memxferfunc read_memory;
 130
 131   /* Function to actually write the target memory */
 132   memxferfunc write_memory;
 133
 134   /* free list */
 135   struct dcache_block *free_head;
 136   struct dcache_block *free_tail;
 137
 138   /* in use list */
 139   struct dcache_block *valid_head;
 140   struct dcache_block *valid_tail;
 141
 142   /* The cache itself. */
 143   struct dcache_block *the_cache;
 144
 145   /* potentially, if the cache was enabled, and then turned off, and
 146      then turned on again, the stuff in it could be stale, so this is
 147      used to mark it */
 148   int cache_has_stuff;
 149 } ;
 150
 151 int remote_dcache = 0;
 152
 153 DCACHE *last_cache; /* Used by info dcache */
 154
 155
 156
 157 /* Free all the data cache blocks, thus discarding all cached data.  */
 158
 159 void
 160 dcache_flush (dcache)
 161      DCACHE *dcache;
 162 {
 163   int i;
 164   dcache->valid_head = 0;
 165   dcache->valid_tail = 0;
 166
 167   dcache->free_head = 0;
 168   dcache->free_tail = 0;
 169
 170   for (i = 0; i < DCACHE_SIZE; i++)
 171     {
 172       struct dcache_block *db = dcache->the_cache + i;
 173
 174       if (!dcache->free_head)
 175         dcache->free_head = db;
 176       else
 177         dcache->free_tail->p = db;
 178       dcache->free_tail = db;
 179       db->p = 0;
 180     }
 181
 182   dcache->cache_has_stuff = 0;
 183
 184   return;
 185 }
 186
 187 /* If addr is present in the dcache, return the address of the block
 188    containing it. */
 189 static
 190 struct dcache_block *
 191 dcache_hit (dcache, addr)
 192      DCACHE *dcache;
 193      unsigned int addr;
 194 {
 195   register struct dcache_block *db;
 196
 197   /* Search all cache blocks for one that is at this address.  */
 198   db = dcache->valid_head;
 199
 200   while (db)
 201     {
 202       if (MASK(addr) == db->addr)
 203         {
 204           db->refs++;
 205           return db;
 206         }
 207       db = db->p;
 208     }
 209
 210   return NULL;
 211 }
 212
 213 /* Make sure that anything in this line which needs to
 214    be written is. */
 215
 216 static int
 217 dcache_write_line (dcache, db)
 218      DCACHE *dcache;
 219      register struct dcache_block *db;
 220 {
 221   int s;
 222   int e;
 223   s = 0;
 224   if (db->anydirty)
 225     {
 226       for (s = 0; s < LINE_SIZE; s++)
 227         {
 228           if (db->state[s] == ENTRY_DIRTY)
 229             {
 230               int len = 0;
 231               for (e = s ; e < LINE_SIZE; e++, len++)
 232                 if (db->state[e] != ENTRY_DIRTY)
 233                   break;
 234               {
 235                 /* all bytes from s..s+len-1 need to
 236                    be written out */
 237                 int done = 0;
 238                 while (done < len) {
 239                   int t = dcache->write_memory (db->addr + s + done,
 240                                                 db->data + s + done,
 241                                                 len - done);
 242                   if (t == 0)
 243                     return 0;
 244                   done += t;
 245                 }
 246                 memset (db->state + s, ENTRY_OK, len);
 247                 s = e;
 248               }
 249             }
 250         }
 251       db->anydirty = 0;
 252     }
 253   return 1;
 254 }
 255
 256
 257 /* Get a free cache block, put or keep it on the valid list,
 258    and return its address.  The caller should store into the block
 259    the address and data that it describes, then remque it from the
 260    free list and insert it into the valid list.  This procedure
 261    prevents errors from creeping in if a memory retrieval is
 262    interrupted (which used to put garbage blocks in the valid
 263    list...).  */
 264 static
 265 struct dcache_block *
 266 dcache_alloc (dcache)
 267      DCACHE *dcache;
 268 {
 269   register struct dcache_block *db;
 270
 271   if (remote_dcache == 0)
 272     abort ();
 273
 274   /* Take something from the free list */
 275   db = dcache->free_head;
 276   if (db)
 277     {
 278       dcache->free_head = db->p;
 279     }
 280   else
 281     {
 282       /* Nothing left on free list, so grab one from the valid list */
 283       db = dcache->valid_head;
 284       dcache->valid_head = db->p;
 285
 286       dcache_write_line (dcache, db);
 287     }
 288
 289   /* append this line to end of valid list */
 290   if (!dcache->valid_head)
 291     dcache->valid_head = db;
 292   else
 293     dcache->valid_tail->p = db;
 294   dcache->valid_tail = db;
 295   db->p = 0;
 296
 297   return db;
 298 }
 299
 300 /* Using the data cache DCACHE return the contents of the byte at
 301    address ADDR in the remote machine.
 302
 303    Returns 0 on error. */
 304
 305 int
 306 dcache_peek_byte (dcache, addr, ptr)
 307      DCACHE *dcache;
 308      CORE_ADDR addr;
 309      char *ptr;
 310 {
 311   register struct dcache_block *db = dcache_hit (dcache, addr);
 312   int ok=1;
 313   int done = 0;
 314   if (db == 0
 315       || db->state[XFORM (addr)] == ENTRY_BAD)
 316     {
 317       if (db)
 318         {
 319           dcache_write_line (dcache, db);
 320         }
 321     else
 322       db = dcache_alloc (dcache);
 323       immediate_quit++;
 324             db->addr = MASK (addr);
 325       while (done < LINE_SIZE)
 326         {
 327           int try =
 328             (*dcache->read_memory)
 329               (db->addr + done,
 330                db->data + done,
 331                LINE_SIZE - done);
 332           if (try == 0)
 333             return 0;
 334           done += try;
 335         }
 336       immediate_quit--;
 337
 338       memset (db->state, ENTRY_OK, sizeof (db->data));
 339       db->anydirty = 0;
 340     }
 341   *ptr = db->data[XFORM (addr)];
 342   return ok;
 343 }
 344
 345 /* Using the data cache DCACHE return the contents of the word at
 346    address ADDR in the remote machine.
 347
 348    Returns 0 on error. */
 349
 350 int
 351 dcache_peek (dcache, addr, data)
 352      DCACHE *dcache;
 353      CORE_ADDR addr;
 354      int *data;
 355 {
 356   char *dp = (char *) data;
 357   int i;
 358   for (i = 0; i < sizeof (int); i++)
 359     {
 360       if (!dcache_peek_byte (dcache, addr + i, dp + i))
 361         return 0;
 362     }
 363   return 1;
 364 }
 365
 366
 367 /* Writeback any dirty lines to the remote. */
 368 static int
 369 dcache_writeback (dcache)
 370      DCACHE *dcache;
 371 {
 372   struct dcache_block *db;
 373
 374   db = dcache->valid_head;
 375
 376   while (db)
 377     {
 378       if (!dcache_write_line (dcache, db))
 379         return 0;
 380       db = db->p;
 381     }
 382   return 1;
 383 }
 384
 385
 386 /* Using the data cache DCACHE return the contents of the word at
 387    address ADDR in the remote machine.  */
 388 int
 389 dcache_fetch (dcache, addr)
 390      DCACHE *dcache;
 391      CORE_ADDR addr;
 392 {
 393   int res;
 394   dcache_peek (dcache, addr, &res);
 395   return res;
 396 }
 397
 398
 399 /* Write the byte at PTR into ADDR in the data cache.
 400    Return zero on write error.
 401  */
 402
 403 int
 404 dcache_poke_byte (dcache, addr, ptr)
 405      DCACHE *dcache;
 406      CORE_ADDR addr;
 407      char *ptr;
 408 {
 409   register struct dcache_block *db = dcache_hit (dcache, addr);
 410
 411   if (!db)
 412     {
 413       db = dcache_alloc (dcache);
 414       db->addr = MASK (addr);
 415       memset (db->state, ENTRY_BAD, sizeof (db->data));
 416     }
 417
 418   db->data[XFORM (addr)] = *ptr;
 419   db->state[XFORM (addr)] = ENTRY_DIRTY;
 420   db->anydirty = 1;
 421   return 1;
 422 }
 423
 424 /* Write the word at ADDR both in the data cache and in the remote machine.
 425    Return zero on write error.
 426  */
 427
 428 int
 429 dcache_poke (dcache, addr, data)
 430      DCACHE *dcache;
 431      CORE_ADDR addr;
 432      int data;
 433 {
 434   char *dp = (char *) (&data);
 435   int i;
 436   for (i = 0; i < sizeof (int); i++)
 437     {
 438       if (!dcache_poke_byte (dcache, addr + i, dp + i))
 439         return 0;
 440     }
 441   dcache_writeback (dcache);
 442   return 1;
 443 }
 444
 445
 446 /* Initialize the data cache.  */
 447 DCACHE *
 448 dcache_init (reading, writing)
 449      memxferfunc reading;
 450      memxferfunc writing;
 451 {
 452   int csize = sizeof (struct dcache_block) * DCACHE_SIZE;
 453   DCACHE *dcache;
 454
 455   dcache = (DCACHE *) xmalloc (sizeof (*dcache));
 456   dcache->read_memory = reading;
 457   dcache->write_memory = writing;
 458
 459   dcache->the_cache = (struct dcache_block *) xmalloc (csize);
 460   memset (dcache->the_cache, 0, csize);
 461
 462   dcache_flush (dcache);
 463
 464   last_cache = dcache;
 465   return dcache;
 466 }
 467
 468 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
 469    to or from debugger address MYADDR.  Write to inferior if SHOULD_WRITE is
 470    nonzero.
 471
 472    Returns length of data written or read; 0 for error.
 473
 474    This routine is indended to be called by remote_xfer_ functions. */
 475
 476 int
 477 dcache_xfer_memory (dcache, memaddr, myaddr, len, should_write)
 478      DCACHE *dcache;
 479      CORE_ADDR memaddr;
 480      char *myaddr;
 481      int len;
 482      int should_write;
 483 {
 484   int i;
 485
 486   if (remote_dcache)
 487     {
 488       int (*xfunc) ()
 489         = should_write ? dcache_poke_byte : dcache_peek_byte;
 490
 491       for (i = 0; i < len; i++)
 492         {
 493           if (!xfunc (dcache, memaddr + i, myaddr + i))
 494             return 0;
 495         }
 496       dcache->cache_has_stuff = 1;
 497       dcache_writeback (dcache);
 498     }
 499   else
 500     {
 501       int (*xfunc) ()
 502         = should_write ? dcache->write_memory : dcache->read_memory;
 503
 504       if (dcache->cache_has_stuff)
 505         dcache_flush (dcache);
 506
 507       len = xfunc (memaddr, myaddr, len);
 508     }
 509   return len;
 510 }
 511
 512 static void
 513 dcache_info (exp, tty)
 514      char *exp;
 515      int tty;
 516 {
 517   struct dcache_block *p;
 518
 519   if (!remote_dcache)
 520     {
 521       printf_filtered ("Dcache not enabled\n");
 522       return;
 523     }
 524   printf_filtered ("Dcache enabled, line width %d, depth %d\n",
 525                    LINE_SIZE, DCACHE_SIZE);
 526
 527   printf_filtered ("Cache state:\n");
 528
 529   for (p = last_cache->valid_head; p; p = p->p)
 530     {
 531       int j;
 532       printf_filtered ("Line at %08xd, referenced %d times\n",
 533                        p->addr, p->refs);
 534
 535       for (j = 0; j < LINE_SIZE; j++)
 536         printf_filtered ("%02x", p->data[j] & 0xFF);
 537       printf_filtered ("\n");
 538
 539       for (j = 0; j < LINE_SIZE; j++)
 540         printf_filtered (" %2x", p->state[j]);
 541       printf_filtered ("\n");
 542     }
 543 }
 544
 545 void
 546 _initialize_dcache ()
 547 {
 548   add_show_from_set
 549     (add_set_cmd ("remotecache", class_support, var_boolean,
 550                   (char *) &remote_dcache,
 551                   "\
 552 Set cache use for remote targets.\n\
 553 When on, use data caching for remote targets.  For many remote targets\n\
 554 this option can offer better throughput for reading target memory.\n\
 555 Unfortunately, gdb does not currently know anything about volatile\n\
 556 registers and thus data caching will produce incorrect results with\n\
 557 volatile registers are in use.  By default, this option is on.",
 558                   &setlist),
 559      &showlist);
 560
 561   add_info ("dcache", dcache_info,
 562             "Print information on the dcache performance.");
 563
 564 }