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