gdb/dcache.c

   1 /* Caching code.  Typically used by remote back ends for
   2    caching remote memory.
   3
   4    Copyright 1992, 1993, 1995, 1998 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 #include "gdbcore.h"
  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   CORE_ADDR 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 static int dcache_poke_byte PARAMS ((DCACHE *dcache, CORE_ADDR addr,
 152                                      char *ptr));
 153
 154 static int dcache_peek_byte PARAMS ((DCACHE *dcache, CORE_ADDR addr,
 155                                      char *ptr));
 156
 157 static struct dcache_block *dcache_hit PARAMS ((DCACHE *dcache,
 158                                                 CORE_ADDR addr));
 159
 160 static int dcache_write_line PARAMS ((DCACHE *dcache,struct dcache_block *db));
 161
 162 static struct dcache_block *dcache_alloc PARAMS ((DCACHE *dcache));
 163
 164 static int dcache_writeback PARAMS ((DCACHE *dcache));
 165
 166 static void dcache_info PARAMS ((char *exp, int tty));
 167
 168 void _initialize_dcache PARAMS ((void));
 169
 170 int remote_dcache = 0;
 171
 172 DCACHE *last_cache; /* Used by info dcache */
 173
 174
 175 /* Free all the data cache blocks, thus discarding all cached data.  */
 176
 177 void
 178 dcache_flush (dcache)
 179      DCACHE *dcache;
 180 {
 181   int i;
 182   dcache->valid_head = 0;
 183   dcache->valid_tail = 0;
 184
 185   dcache->free_head = 0;
 186   dcache->free_tail = 0;
 187
 188   for (i = 0; i < DCACHE_SIZE; i++)
 189     {
 190       struct dcache_block *db = dcache->the_cache + i;
 191
 192       if (!dcache->free_head)
 193         dcache->free_head = db;
 194       else
 195         dcache->free_tail->p = db;
 196       dcache->free_tail = db;
 197       db->p = 0;
 198     }
 199
 200   dcache->cache_has_stuff = 0;
 201
 202   return;
 203 }
 204
 205 /* If addr is present in the dcache, return the address of the block
 206    containing it. */
 207
 208 static struct dcache_block *
 209 dcache_hit (dcache, addr)
 210      DCACHE *dcache;
 211      CORE_ADDR addr;
 212 {
 213   register struct dcache_block *db;
 214
 215   /* Search all cache blocks for one that is at this address.  */
 216   db = dcache->valid_head;
 217
 218   while (db)
 219     {
 220       if (MASK(addr) == db->addr)
 221         {
 222           db->refs++;
 223           return db;
 224         }
 225       db = db->p;
 226     }
 227
 228   return NULL;
 229 }
 230
 231 /* Make sure that anything in this line which needs to
 232    be written is. */
 233
 234 static int
 235 dcache_write_line (dcache, db)
 236      DCACHE *dcache;
 237      register struct dcache_block *db;
 238 {
 239   int s;
 240   int e;
 241   s = 0;
 242   if (db->anydirty)
 243     {
 244       for (s = 0; s < LINE_SIZE; s++)
 245         {
 246           if (db->state[s] == ENTRY_DIRTY)
 247             {
 248               int len = 0;
 249               for (e = s ; e < LINE_SIZE; e++, len++)
 250                 if (db->state[e] != ENTRY_DIRTY)
 251                   break;
 252               {
 253                 /* all bytes from s..s+len-1 need to
 254                    be written out */
 255                 int done = 0;
 256                 while (done < len) {
 257                   int t = dcache->write_memory (db->addr + s + done,
 258                                                 db->data + s + done,
 259                                                 len - done);
 260                   if (t == 0)
 261                     return 0;
 262                   done += t;
 263                 }
 264                 memset (db->state + s, ENTRY_OK, len);
 265                 s = e;
 266               }
 267             }
 268         }
 269       db->anydirty = 0;
 270     }
 271   return 1;
 272 }
 273
 274
 275 /* Get a free cache block, put or keep it on the valid list,
 276    and return its address.  The caller should store into the block
 277    the address and data that it describes, then remque it from the
 278    free list and insert it into the valid list.  This procedure
 279    prevents errors from creeping in if a memory retrieval is
 280    interrupted (which used to put garbage blocks in the valid
 281    list...).  */
 282
 283 static struct dcache_block *
 284 dcache_alloc (dcache)
 285      DCACHE *dcache;
 286 {
 287   register struct dcache_block *db;
 288
 289   if (remote_dcache == 0)
 290     abort ();
 291
 292   /* Take something from the free list */
 293   db = dcache->free_head;
 294   if (db)
 295     {
 296       dcache->free_head = db->p;
 297     }
 298   else
 299     {
 300       /* Nothing left on free list, so grab one from the valid list */
 301       db = dcache->valid_head;
 302       dcache->valid_head = db->p;
 303
 304       dcache_write_line (dcache, db);
 305     }
 306
 307   /* append this line to end of valid list */
 308   if (!dcache->valid_head)
 309     dcache->valid_head = db;
 310   else
 311     dcache->valid_tail->p = db;
 312   dcache->valid_tail = db;
 313   db->p = 0;
 314
 315   return db;
 316 }
 317
 318 /* Using the data cache DCACHE return the contents of the byte at
 319    address ADDR in the remote machine.
 320
 321    Returns 0 on error. */
 322
 323 static int
 324 dcache_peek_byte (dcache, addr, ptr)
 325      DCACHE *dcache;
 326      CORE_ADDR addr;
 327      char *ptr;
 328 {
 329   register struct dcache_block *db = dcache_hit (dcache, addr);
 330   int ok=1;
 331   int done = 0;
 332   if (db == 0
 333       || db->state[XFORM (addr)] == ENTRY_BAD)
 334     {
 335       if (db)
 336         {
 337           dcache_write_line (dcache, db);
 338         }
 339     else
 340       db = dcache_alloc (dcache);
 341       immediate_quit++;
 342       db->addr = MASK (addr);
 343       while (done < LINE_SIZE)
 344         {
 345           int try =
 346             (*dcache->read_memory)
 347               (db->addr + done,
 348                db->data + done,
 349                LINE_SIZE - done);
 350           if (try == 0)
 351             return 0;
 352           done += try;
 353         }
 354       immediate_quit--;
 355
 356       memset (db->state, ENTRY_OK, sizeof (db->data));
 357       db->anydirty = 0;
 358     }
 359   *ptr = db->data[XFORM (addr)];
 360   return ok;
 361 }
 362
 363 /* Writeback any dirty lines to the remote. */
 364 static int
 365 dcache_writeback (dcache)
 366      DCACHE *dcache;
 367 {
 368   struct dcache_block *db;
 369
 370   db = dcache->valid_head;
 371
 372   while (db)
 373     {
 374       if (!dcache_write_line (dcache, db))
 375         return 0;
 376       db = db->p;
 377     }
 378   return 1;
 379 }
 380
 381
 382 /* Using the data cache DCACHE return the contents of the word at
 383    address ADDR in the remote machine.  */
 384 int
 385 dcache_fetch (dcache, addr)
 386      DCACHE *dcache;
 387      CORE_ADDR addr;
 388 {
 389   int res;
 390
 391   if (dcache_xfer_memory (dcache, addr, (char *)&res, sizeof res, 0) != sizeof res)
 392     memory_error (EIO, addr);
 393
 394   return res;
 395 }
 396
 397
 398 /* Write the byte at PTR into ADDR in the data cache.
 399    Return zero on write error.
 400  */
 401
 402 static int
 403 dcache_poke_byte (dcache, addr, ptr)
 404      DCACHE *dcache;
 405      CORE_ADDR addr;
 406      char *ptr;
 407 {
 408   register struct dcache_block *db = dcache_hit (dcache, addr);
 409
 410   if (!db)
 411     {
 412       db = dcache_alloc (dcache);
 413       db->addr = MASK (addr);
 414       memset (db->state, ENTRY_BAD, sizeof (db->data));
 415     }
 416
 417   db->data[XFORM (addr)] = *ptr;
 418   db->state[XFORM (addr)] = ENTRY_DIRTY;
 419   db->anydirty = 1;
 420   return 1;
 421 }
 422
 423 /* Write the word at ADDR both in the data cache and in the remote machine.
 424    Return zero on write error.
 425  */
 426
 427 int
 428 dcache_poke (dcache, addr, data)
 429      DCACHE *dcache;
 430      CORE_ADDR addr;
 431      int data;
 432 {
 433   if (dcache_xfer_memory (dcache, addr, (char *)&data, sizeof data, 1) != sizeof data)
 434     return 0;
 435
 436   return dcache_writeback (dcache);
 437 }
 438
 439
 440 /* Initialize the data cache.  */
 441 DCACHE *
 442 dcache_init (reading, writing)
 443      memxferfunc reading;
 444      memxferfunc writing;
 445 {
 446   int csize = sizeof (struct dcache_block) * DCACHE_SIZE;
 447   DCACHE *dcache;
 448
 449   dcache = (DCACHE *) xmalloc (sizeof (*dcache));
 450   dcache->read_memory = reading;
 451   dcache->write_memory = writing;
 452
 453   dcache->the_cache = (struct dcache_block *) xmalloc (csize);
 454   memset (dcache->the_cache, 0, csize);
 455
 456   dcache_flush (dcache);
 457
 458   last_cache = dcache;
 459   return dcache;
 460 }
 461
 462 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
 463    to or from debugger address MYADDR.  Write to inferior if SHOULD_WRITE is
 464    nonzero.
 465
 466    Returns length of data written or read; 0 for error.
 467
 468    This routine is indended to be called by remote_xfer_ functions. */
 469
 470 int
 471 dcache_xfer_memory (dcache, memaddr, myaddr, len, should_write)
 472      DCACHE *dcache;
 473      CORE_ADDR memaddr;
 474      char *myaddr;
 475      int len;
 476      int should_write;
 477 {
 478   int i;
 479
 480   if (remote_dcache)
 481     {
 482       int (*xfunc) PARAMS ((DCACHE *dcache, CORE_ADDR addr, char *ptr));
 483       xfunc = should_write ? dcache_poke_byte : dcache_peek_byte;
 484
 485       for (i = 0; i < len; i++)
 486         {
 487           if (!xfunc (dcache, memaddr + i, myaddr + i))
 488             return 0;
 489         }
 490       dcache->cache_has_stuff = 1;
 491       dcache_writeback (dcache);
 492     }
 493   else
 494     {
 495       memxferfunc xfunc;
 496       xfunc = should_write ? dcache->write_memory : dcache->read_memory;
 497
 498       if (dcache->cache_has_stuff)
 499         dcache_flush (dcache);
 500
 501       len = xfunc (memaddr, myaddr, len);
 502     }
 503   return len;
 504 }
 505
 506 static void
 507 dcache_info (exp, tty)
 508      char *exp;
 509      int tty;
 510 {
 511   struct dcache_block *p;
 512
 513   if (!remote_dcache)
 514     {
 515       printf_filtered ("Dcache not enabled\n");
 516       return;
 517     }
 518   printf_filtered ("Dcache enabled, line width %d, depth %d\n",
 519                    LINE_SIZE, DCACHE_SIZE);
 520
 521   printf_filtered ("Cache state:\n");
 522
 523   for (p = last_cache->valid_head; p; p = p->p)
 524     {
 525       int j;
 526       printf_filtered ("Line at %08xd, referenced %d times\n",
 527                        p->addr, p->refs);
 528
 529       for (j = 0; j < LINE_SIZE; j++)
 530         printf_filtered ("%02x", p->data[j] & 0xFF);
 531       printf_filtered ("\n");
 532
 533       for (j = 0; j < LINE_SIZE; j++)
 534         printf_filtered (" %2x", p->state[j]);
 535       printf_filtered ("\n");
 536     }
 537 }
 538
 539 void
 540 _initialize_dcache ()
 541 {
 542   add_show_from_set
 543     (add_set_cmd ("remotecache", class_support, var_boolean,
 544                   (char *) &remote_dcache,
 545                   "\
 546 Set cache use for remote targets.\n\
 547 When on, use data caching for remote targets.  For many remote targets\n\
 548 this option can offer better throughput for reading target memory.\n\
 549 Unfortunately, gdb does not currently know anything about volatile\n\
 550 registers and thus data caching will produce incorrect results with\n\
 551 volatile registers are in use.  By default, this option is on.",
 552                   &setlist),
 553      &showlist);
 554
 555   add_info ("dcache", dcache_info,
 556             "Print information on the dcache performance.");
 557
 558 }