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/* Caching code for GDB, the GNU debugger.

   Copyright (C) 1992, 1993, 1995, 1996, 1998, 1999, 2000, 2001, 2003, 2007,

   2008, 2009, 2010 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"

#include "dcache.h"

#include "gdbcmd.h"

#include "gdb_string.h"

#include "gdbcore.h"

#include "target.h"

#include "inferior.h"

#include "splay-tree.h"

/* The data cache could lead to incorrect results because it doesn't

   know about volatile variables, thus making it impossible to debug

   functions which use memory mapped I/O devices.  Set the nocache

   memory region attribute in those cases.

   In general the dcache speeds up performance.  Some speed improvement

   comes from the actual caching mechanism, but the major gain is in

   the reduction of the remote protocol overhead; instead of reading

   or writing a large area of memory in 4 byte requests, the cache

   bundles up the requests into LINE_SIZE chunks, reducing overhead

   significantly.  This is most useful when accessing a large amount

   of data, such as when performing a backtrace.

   The cache is a splay tree along with a linked list for replacement.

   Each block caches a LINE_SIZE area of memory.  Within each line we

   remember the address of the line (which must be a multiple of

   LINE_SIZE) and the actual data block.

   Lines are only allocated as needed, so DCACHE_SIZE really specifies the

   *maximum* number of lines in the cache.

   At present, the cache is write-through rather than writeback: as soon

   as data is written to the cache, it is also immediately written to

   the target.  Therefore, cache lines are never "dirty".  Whether a given

   line is valid or not depends on where it is stored in the dcache_struct;

   there is no per-block valid flag.  */

/* NOTE: Interaction of dcache and memory region attributes

   As there is no requirement that memory region attributes be aligned

   to or be a multiple of the dcache page size, dcache_read_line() and

   dcache_write_line() must break up the page by memory region.  If a

   chunk does not have the cache attribute set, an invalid memory type

   is set, etc., then the chunk is skipped.  Those chunks are handled

   in target_xfer_memory() (or target_xfer_memory_partial()).

   This doesn't occur very often.  The most common occurance is when

   the last bit of the .text segment and the first bit of the .data

   segment fall within the same dcache page with a ro/cacheable memory

   region defined for the .text segment and a rw/non-cacheable memory

   region defined for the .data segment.  */

/* The maximum number of lines stored.  The total size of the cache is

   equal to DCACHE_SIZE times LINE_SIZE.  */

#define DCACHE_SIZE 4096

/* The size of a cache line.  Smaller values reduce the time taken to

   read a single byte and make the cache more granular, but increase

   overhead and reduce the effectiveness of the cache as a prefetcher.  */

#define LINE_SIZE_POWER 6

#define LINE_SIZE (1 << LINE_SIZE_POWER)

/* Each cache block holds LINE_SIZE bytes of data

   starting at a multiple-of-LINE_SIZE address.  */

#define LINE_SIZE_MASK  ((LINE_SIZE - 1))

#define XFORM(x)        ((x) & LINE_SIZE_MASK)

#define MASK(x)         ((x) & ~LINE_SIZE_MASK)

struct dcache_block

{

  /* for least-recently-allocated and free lists */

  struct dcache_block *prev;

  struct dcache_block *next;

  CORE_ADDR addr;               /* address of data */

  gdb_byte data[LINE_SIZE];     /* bytes at given address */

  int refs;                     /* # hits */

};

struct dcache_struct

{

  splay_tree tree;

  struct dcache_block *oldest; /* least-recently-allocated list */

  /* The free list is maintained identically to OLDEST to simplify

     the code: we only need one set of accessors.  */

  struct dcache_block *freelist;

  /* The number of in-use lines in the cache.  */

  int size;

  /* The ptid of last inferior to use cache or null_ptid.  */

  ptid_t ptid;

};

typedef void (block_func) (struct dcache_block *block, void *param);

static struct dcache_block *dcache_hit (DCACHE *dcache, CORE_ADDR addr);

static int dcache_read_line (DCACHE *dcache, struct dcache_block *db);

static struct dcache_block *dcache_alloc (DCACHE *dcache, CORE_ADDR addr);

static void dcache_info (char *exp, int tty);

void _initialize_dcache (void);

static int dcache_enabled_p = 0; /* OBSOLETE */

static void

show_dcache_enabled_p (struct ui_file *file, int from_tty,

                       struct cmd_list_element *c, const char *value)

{

  fprintf_filtered (file, _("Deprecated remotecache flag is %s.\n"), value);

}

static DCACHE *last_cache; /* Used by info dcache */

/* Add BLOCK to circular block list BLIST, behind the block at *BLIST.

   *BLIST is not updated (unless it was previously NULL of course).

   This is for the least-recently-allocated list's sake:

   BLIST points to the oldest block.

   ??? This makes for poor cache usage of the free list,

   but is it measurable?  */

static void

append_block (struct dcache_block **blist, struct dcache_block *block)

{

  if (*blist)

    {

      block->next = *blist;

      block->prev = (*blist)->prev;

      block->prev->next = block;

      (*blist)->prev = block;

      /* We don't update *BLIST here to maintain the invariant that for the

         least-recently-allocated list *BLIST points to the oldest block.  */

    }

  else

    {

      block->next = block;

      block->prev = block;

      *blist = block;

    }

}

/* Remove BLOCK from circular block list BLIST.  */

static void

remove_block (struct dcache_block **blist, struct dcache_block *block)

{

  if (block->next == block)

    {

      *blist = NULL;

    }

  else

    {

      block->next->prev = block->prev;

      block->prev->next = block->next;

      /* If we removed the block *BLIST points to, shift it to the next block

         to maintain the invariant that for the least-recently-allocated list

         *BLIST points to the oldest block.  */

      if (*blist == block)

        *blist = block->next;

    }

}

/* Iterate over all elements in BLIST, calling FUNC.

   PARAM is passed to FUNC.

   FUNC may remove the block it's passed, but only that block.  */

static void

for_each_block (struct dcache_block **blist, block_func *func, void *param)

{

  struct dcache_block *db;

  if (*blist == NULL)

    return;

  db = *blist;

  do

    {

      struct dcache_block *next = db->next;

      func (db, param);

      db = next;

    }

  while (*blist && db != *blist);

}

/* BLOCK_FUNC function for dcache_invalidate.

   This doesn't remove the block from the oldest list on purpose.

   dcache_invalidate will do it later.  */

static void

invalidate_block (struct dcache_block *block, void *param)

{

  DCACHE *dcache = (DCACHE *) param;

  splay_tree_remove (dcache->tree, (splay_tree_key) block->addr);

  append_block (&dcache->freelist, block);

}

/* Free all the data cache blocks, thus discarding all cached data.  */

void

dcache_invalidate (DCACHE *dcache)

{

  for_each_block (&dcache->oldest, invalidate_block, dcache);

  dcache->oldest = NULL;

  dcache->size = 0;

  dcache->ptid = null_ptid;

}

/* Invalidate the line associated with ADDR.  */

static void

dcache_invalidate_line (DCACHE *dcache, CORE_ADDR addr)

{

  struct dcache_block *db = dcache_hit (dcache, addr);

  if (db)

    {

      splay_tree_remove (dcache->tree, (splay_tree_key) db->addr);

      remove_block (&dcache->oldest, db);

      append_block (&dcache->freelist, db);

      --dcache->size;

    }

}

/* If addr is present in the dcache, return the address of the block

   containing it.  Otherwise return NULL.  */

static struct dcache_block *

dcache_hit (DCACHE *dcache, CORE_ADDR addr)

{

  struct dcache_block *db;

  splay_tree_node node = splay_tree_lookup (dcache->tree,

                                            (splay_tree_key) MASK (addr));

  if (!node)

    return NULL;

  db = (struct dcache_block *) node->value;

  db->refs++;

  return db;

}

/* Fill a cache line from target memory.

   The result is 1 for success, 0 if the (entire) cache line

   wasn't readable.  */

static int

dcache_read_line (DCACHE *dcache, struct dcache_block *db)

{

  CORE_ADDR memaddr;

  gdb_byte *myaddr;

  int len;

  int res;

  int reg_len;

  struct mem_region *region;

  len = LINE_SIZE;

  memaddr = db->addr;

  myaddr  = db->data;

  while (len > 0)

    {

      /* Don't overrun if this block is right at the end of the region.  */

      region = lookup_mem_region (memaddr);

      if (region->hi == 0 || memaddr + len < region->hi)

        reg_len = len;

      else

        reg_len = region->hi - memaddr;

      /* Skip non-readable regions.  The cache attribute can be ignored,

         since we may be loading this for a stack access.  */

      if (region->attrib.mode == MEM_WO)

        {

          memaddr += reg_len;

          myaddr  += reg_len;

          len     -= reg_len;

          continue;

        }

      res = target_read (&current_target, TARGET_OBJECT_RAW_MEMORY,

                         NULL, myaddr, memaddr, reg_len);

      if (res < reg_len)

        return 0;

      memaddr += res;

      myaddr += res;

      len -= res;

    }

  return 1;

}

/* Get a free cache block, put or keep it on the valid list,

   and return its address.  */

static struct dcache_block *

dcache_alloc (DCACHE *dcache, CORE_ADDR addr)

{

  struct dcache_block *db;

  if (dcache->size >= DCACHE_SIZE)

    {

      /* Evict the least recently allocated line.  */

      db = dcache->oldest;

      remove_block (&dcache->oldest, db);

      splay_tree_remove (dcache->tree, (splay_tree_key) db->addr);

    }

  else

    {

      db = dcache->freelist;

      if (db)

        remove_block (&dcache->freelist, db);

      else

        db = xmalloc (sizeof (struct dcache_block));

      dcache->size++;

    }

  db->addr = MASK (addr);

  db->refs = 0;

  /* Put DB at the end of the list, it's the newest.  */

  append_block (&dcache->oldest, db);

  splay_tree_insert (dcache->tree, (splay_tree_key) db->addr,

                     (splay_tree_value) db);

  return db;

}

/* Using the data cache DCACHE, store in *PTR the contents of the byte at

   address ADDR in the remote machine.

   Returns 1 for success, 0 for error.  */

static int

dcache_peek_byte (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr)

{

  struct dcache_block *db = dcache_hit (dcache, addr);

  if (!db)

    {

      db = dcache_alloc (dcache, addr);

      if (!dcache_read_line (dcache, db))

         return 0;

    }

  *ptr = db->data[XFORM (addr)];

  return 1;

}

/* Write the byte at PTR into ADDR in the data cache.

   The caller is responsible for also promptly writing the data

   through to target memory.

   If addr is not in cache, this function does nothing; writing to

   an area of memory which wasn't present in the cache doesn't cause

   it to be loaded in.

   Always return 1 (meaning success) to simplify dcache_xfer_memory.  */

static int

dcache_poke_byte (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr)

{

  struct dcache_block *db = dcache_hit (dcache, addr);

  if (db)

    db->data[XFORM (addr)] = *ptr;

  return 1;

}

static int

dcache_splay_tree_compare (splay_tree_key a, splay_tree_key b)

{

  if (a > b)

    return 1;

  else if (a == b)

    return 0;

  else

    return -1;

}

/* Allocate and initialize a data cache.  */

DCACHE *

dcache_init (void)

{

  DCACHE *dcache;

  int i;

  dcache = (DCACHE *) xmalloc (sizeof (*dcache));

  dcache->tree = splay_tree_new (dcache_splay_tree_compare,

                                 NULL,

                                 NULL);

  dcache->oldest = NULL;

  dcache->freelist = NULL;

  dcache->size = 0;

  dcache->ptid = null_ptid;

  last_cache = dcache;

  return dcache;

}

/* BLOCK_FUNC routine for dcache_free.  */

static void

free_block (struct dcache_block *block, void *param)

{

  free (block);

}

/* Free a data cache.  */

void

dcache_free (DCACHE *dcache)

{

  if (last_cache == dcache)

    last_cache = NULL;

  splay_tree_delete (dcache->tree);

  for_each_block (&dcache->oldest, free_block, NULL);

  for_each_block (&dcache->freelist, free_block, NULL);

  xfree (dcache);

}

/* Read or write LEN bytes from inferior memory at MEMADDR, transferring

   to or from debugger address MYADDR.  Write to inferior if SHOULD_WRITE is

   nonzero.

   Return the number of bytes actually transfered, or -1 if the

   transfer is not supported or otherwise fails.  Return of a non-negative

   value less than LEN indicates that no further transfer is possible.

   NOTE: This is different than the to_xfer_partial interface, in which

   positive values less than LEN mean further transfers may be possible.  */

int

dcache_xfer_memory (struct target_ops *ops, DCACHE *dcache,

                    CORE_ADDR memaddr, gdb_byte *myaddr,

                    int len, int should_write)

{

  int i;

  int res;

  int (*xfunc) (DCACHE *dcache, CORE_ADDR addr, gdb_byte *ptr);

  xfunc = should_write ? dcache_poke_byte : dcache_peek_byte;

  /* If this is a different inferior from what we've recorded,

     flush the cache.  */

  if (! ptid_equal (inferior_ptid, dcache->ptid))

    {

      dcache_invalidate (dcache);

      dcache->ptid = inferior_ptid;

    }

  /* Do write-through first, so that if it fails, we don't write to

     the cache at all.  */

  if (should_write)

    {

      res = target_write (ops, TARGET_OBJECT_RAW_MEMORY,

                          NULL, myaddr, memaddr, len);

      if (res <= 0)

        return res;

      /* Update LEN to what was actually written.  */

      len = res;

    }

  for (i = 0; i < len; i++)

    {

      if (!xfunc (dcache, memaddr + i, myaddr + i))

        {

          /* That failed.  Discard its cache line so we don't have a

             partially read line.  */

          dcache_invalidate_line (dcache, memaddr + i);

          /* If we're writing, we still wrote LEN bytes.  */

          if (should_write)

            return len;

          else

            return i;

        }

    }

  return len;

}

/* FIXME: There would be some benefit to making the cache write-back and

   moving the writeback operation to a higher layer, as it could occur

   after a sequence of smaller writes have been completed (as when a stack

   frame is constructed for an inferior function call).  Note that only

   moving it up one level to target_xfer_memory[_partial]() is not

   sufficient since we want to coalesce memory transfers that are

   "logically" connected but not actually a single call to one of the

   memory transfer functions.  */

/* Just update any cache lines which are already present.  This is called

   by memory_xfer_partial in cases where the access would otherwise not go

   through the cache.  */

void

dcache_update (DCACHE *dcache, CORE_ADDR memaddr, gdb_byte *myaddr, int len)

{

  int i;

  for (i = 0; i < len; i++)

    dcache_poke_byte (dcache, memaddr + i, myaddr + i);

}

static void

dcache_print_line (int index)

{

  splay_tree_node n;

  struct dcache_block *db;

  int i, j;

  if (!last_cache)

    {

      printf_filtered (_("No data cache available.\n"));

      return;

    }

  n = splay_tree_min (last_cache->tree);

  for (i = index; i > 0; --i)

    {

      if (!n)

        break;

      n = splay_tree_successor (last_cache->tree, n->key);

    }

  if (!n)

    {

      printf_filtered (_("No such cache line exists.\n"));

      return;

    }

  db = (struct dcache_block *) n->value;

  printf_filtered (_("Line %d: address %s [%d hits]\n"),

                   index, paddress (target_gdbarch, db->addr), db->refs);

  for (j = 0; j < LINE_SIZE; j++)

    {

      printf_filtered ("%02x ", db->data[j]);

      /* Print a newline every 16 bytes (48 characters) */

      if ((j % 16 == 15) && (j != LINE_SIZE - 1))

        printf_filtered ("\n");

    }

  printf_filtered ("\n");

}

static void

dcache_info (char *exp, int tty)

{

  splay_tree_node n;

  int i, refcount, lineno;

  if (exp)

    {

      char *linestart;

      i = strtol (exp, &linestart, 10);

      if (linestart == exp || i < 0)

        {

          printf_filtered (_("Usage: info dcache [linenumber]\n"));

          return;

        }

      dcache_print_line (i);

      return;

    }

  printf_filtered (_("Dcache line width %d, maximum size %d\n"),

                   LINE_SIZE, DCACHE_SIZE);

  if (!last_cache || ptid_equal (last_cache->ptid, null_ptid))

    {

      printf_filtered (_("No data cache available.\n"));

      return;

    }

  printf_filtered (_("Contains data for %s\n"),

                   target_pid_to_str (last_cache->ptid));

  refcount = 0;

  n = splay_tree_min (last_cache->tree);

  i = 0;

  while (n)

    {

      struct dcache_block *db = (struct dcache_block *) n->value;

      printf_filtered (_("Line %d: address %s [%d hits]\n"),

                       i, paddress (target_gdbarch, db->addr), db->refs);

      i++;

      refcount += db->refs;

      n = splay_tree_successor (last_cache->tree, n->key);

    }

  printf_filtered (_("Cache state: %d active lines, %d hits\n"), i, refcount);

}

void

_initialize_dcache (void)

{

  add_setshow_boolean_cmd ("remotecache", class_support,

                           &dcache_enabled_p, _("\

Set cache use for remote targets."), _("\

Show cache use for remote targets."), _("\

This used to enable the data cache for remote targets.  The cache\n\

functionality is now controlled by the memory region system and the\n\

\"stack-cache\" flag; \"remotecache\" now does nothing and\n\

exists only for compatibility reasons."),

                           NULL,

                           show_dcache_enabled_p,

                           &setlist, &showlist);

  add_info ("dcache", dcache_info,

            _("\

Print information on the dcache performance.\n\

With no arguments, this command prints the cache configuration and a\n\

summary of each line in the cache.  Use \"info dcache <lineno> to dump\"\n\

the contents of a given line."));

}