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authorStan Shebs <shebs@codesourcery.com>1999-04-16 01:34:07 +0000
committerStan Shebs <shebs@codesourcery.com>1999-04-16 01:34:07 +0000
commit071ea11e85eb9d529cc5eb3d35f6247466a21b99 (patch)
tree5deda65b8d7b04d1f4cbc534c3206d328e1267ec /gdb/dcache.c
parent1730ec6b1848f0f32154277f788fb29f88d8475b (diff)
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Initial creation of sourceware repository
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diff --git a/gdb/dcache.c b/gdb/dcache.c
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-/* Caching code. Typically used by remote back ends for
- caching remote memory.
-
- Copyright 1992, 1993, 1995, 1998 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 2 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, write to the Free Software
- Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
-
-#include "defs.h"
-#include "dcache.h"
-#include "gdbcmd.h"
-#include "gdb_string.h"
-#include "gdbcore.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 remotecache 0
-
- 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 32 byte (actually LINE_SIZE) chunks.
- Reducing the overhead to an eighth of what it was. This is very
- obvious when displaying a large amount of data,
-
- eg, x/200x 0
-
- caching | no yes
- ----------------------------
- first time | 4 sec 2 sec improvement due to chunking
- second time | 4 sec 0 sec improvement due to caching
-
- The cache structure is unusual, we keep a number of cache blocks
- (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
- Within each line we remember the address of the line (always a
- multiple of the LINE_SIZE) and a vector of bytes over the range.
- There's another vector which contains the state of the bytes.
-
- ENTRY_BAD means that the byte is just plain wrong, and has no
- correspondence with anything else (as it would when the cache is
- turned on, but nothing has been done to it.
-
- ENTRY_DIRTY means that the byte has some data in it which should be
- written out to the remote target one day, but contains correct
- data. ENTRY_OK means that the data is the same in the cache as it
- is in remote memory.
-
-
- The ENTRY_DIRTY state is necessary because GDB likes to write large
- lumps of memory in small bits. If the caching mechanism didn't
- maintain the DIRTY information, then something like a two byte
- write would mean that the entire cache line would have to be read,
- the two bytes modified and then written out again. The alternative
- would be to not read in the cache line in the first place, and just
- write the two bytes directly into target memory. The trouble with
- that is that it really nails performance, because of the remote
- protocol overhead. This way, all those little writes are bundled
- up into an entire cache line write in one go, without having to
- read the cache line in the first place.
-
-
- */
-
-
-/* This value regulates the number of cache blocks stored.
- Smaller values reduce the time spent searching for a cache
- line, and reduce memory requirements, but increase the risk
- of a line not being in memory */
-
-#define DCACHE_SIZE 64
-
-/* This value regulates the size of a cache line. Smaller values
- reduce the time taken to read a single byte, but reduce overall
- throughput. */
-
-#define LINE_SIZE_POWER (5)
-#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)
-
-
-#define ENTRY_BAD 0 /* data at this byte is wrong */
-#define ENTRY_DIRTY 1 /* data at this byte needs to be written back */
-#define ENTRY_OK 2 /* data at this byte is same as in memory */
-
-
-struct dcache_block
-{
- struct dcache_block *p; /* next in list */
- CORE_ADDR addr; /* Address for which data is recorded. */
- char data[LINE_SIZE]; /* bytes at given address */
- unsigned char state[LINE_SIZE]; /* what state the data is in */
-
- /* whether anything in state is dirty - used to speed up the
- dirty scan. */
- int anydirty;
-
- int refs;
-};
-
-
-struct dcache_struct
-{
- /* Function to actually read the target memory. */
- memxferfunc read_memory;
-
- /* Function to actually write the target memory */
- memxferfunc write_memory;
-
- /* free list */
- struct dcache_block *free_head;
- struct dcache_block *free_tail;
-
- /* in use list */
- struct dcache_block *valid_head;
- struct dcache_block *valid_tail;
-
- /* The cache itself. */
- struct dcache_block *the_cache;
-
- /* potentially, if the cache was enabled, and then turned off, and
- then turned on again, the stuff in it could be stale, so this is
- used to mark it */
- int cache_has_stuff;
-} ;
-
-static int dcache_poke_byte PARAMS ((DCACHE *dcache, CORE_ADDR addr,
- char *ptr));
-
-static int dcache_peek_byte PARAMS ((DCACHE *dcache, CORE_ADDR addr,
- char *ptr));
-
-static struct dcache_block *dcache_hit PARAMS ((DCACHE *dcache,
- CORE_ADDR addr));
-
-static int dcache_write_line PARAMS ((DCACHE *dcache,struct dcache_block *db));
-
-static struct dcache_block *dcache_alloc PARAMS ((DCACHE *dcache));
-
-static int dcache_writeback PARAMS ((DCACHE *dcache));
-
-static void dcache_info PARAMS ((char *exp, int tty));
-
-void _initialize_dcache PARAMS ((void));
-
-int remote_dcache = 0;
-
-DCACHE *last_cache; /* Used by info dcache */
-
-
-/* Free all the data cache blocks, thus discarding all cached data. */
-
-void
-dcache_flush (dcache)
- DCACHE *dcache;
-{
- int i;
- dcache->valid_head = 0;
- dcache->valid_tail = 0;
-
- dcache->free_head = 0;
- dcache->free_tail = 0;
-
- for (i = 0; i < DCACHE_SIZE; i++)
- {
- struct dcache_block *db = dcache->the_cache + i;
-
- if (!dcache->free_head)
- dcache->free_head = db;
- else
- dcache->free_tail->p = db;
- dcache->free_tail = db;
- db->p = 0;
- }
-
- dcache->cache_has_stuff = 0;
-
- return;
-}
-
-/* If addr is present in the dcache, return the address of the block
- containing it. */
-
-static struct dcache_block *
-dcache_hit (dcache, addr)
- DCACHE *dcache;
- CORE_ADDR addr;
-{
- register struct dcache_block *db;
-
- /* Search all cache blocks for one that is at this address. */
- db = dcache->valid_head;
-
- while (db)
- {
- if (MASK(addr) == db->addr)
- {
- db->refs++;
- return db;
- }
- db = db->p;
- }
-
- return NULL;
-}
-
-/* Make sure that anything in this line which needs to
- be written is. */
-
-static int
-dcache_write_line (dcache, db)
- DCACHE *dcache;
- register struct dcache_block *db;
-{
- int s;
- int e;
- s = 0;
- if (db->anydirty)
- {
- for (s = 0; s < LINE_SIZE; s++)
- {
- if (db->state[s] == ENTRY_DIRTY)
- {
- int len = 0;
- for (e = s ; e < LINE_SIZE; e++, len++)
- if (db->state[e] != ENTRY_DIRTY)
- break;
- {
- /* all bytes from s..s+len-1 need to
- be written out */
- int done = 0;
- while (done < len) {
- int t = dcache->write_memory (db->addr + s + done,
- db->data + s + done,
- len - done);
- if (t == 0)
- return 0;
- done += t;
- }
- memset (db->state + s, ENTRY_OK, len);
- s = e;
- }
- }
- }
- db->anydirty = 0;
- }
- return 1;
-}
-
-
-/* Get a free cache block, put or keep it on the valid list,
- and return its address. The caller should store into the block
- the address and data that it describes, then remque it from the
- free list and insert it into the valid list. This procedure
- prevents errors from creeping in if a memory retrieval is
- interrupted (which used to put garbage blocks in the valid
- list...). */
-
-static struct dcache_block *
-dcache_alloc (dcache)
- DCACHE *dcache;
-{
- register struct dcache_block *db;
-
- if (remote_dcache == 0)
- abort ();
-
- /* Take something from the free list */
- db = dcache->free_head;
- if (db)
- {
- dcache->free_head = db->p;
- }
- else
- {
- /* Nothing left on free list, so grab one from the valid list */
- db = dcache->valid_head;
- dcache->valid_head = db->p;
-
- dcache_write_line (dcache, db);
- }
-
- /* append this line to end of valid list */
- if (!dcache->valid_head)
- dcache->valid_head = db;
- else
- dcache->valid_tail->p = db;
- dcache->valid_tail = db;
- db->p = 0;
-
- return db;
-}
-
-/* Using the data cache DCACHE return the contents of the byte at
- address ADDR in the remote machine.
-
- Returns 0 on error. */
-
-static int
-dcache_peek_byte (dcache, addr, ptr)
- DCACHE *dcache;
- CORE_ADDR addr;
- char *ptr;
-{
- register struct dcache_block *db = dcache_hit (dcache, addr);
- int ok=1;
- int done = 0;
- if (db == 0
- || db->state[XFORM (addr)] == ENTRY_BAD)
- {
- if (db)
- {
- dcache_write_line (dcache, db);
- }
- else
- db = dcache_alloc (dcache);
- immediate_quit++;
- db->addr = MASK (addr);
- while (done < LINE_SIZE)
- {
- int try =
- (*dcache->read_memory)
- (db->addr + done,
- db->data + done,
- LINE_SIZE - done);
- if (try == 0)
- return 0;
- done += try;
- }
- immediate_quit--;
-
- memset (db->state, ENTRY_OK, sizeof (db->data));
- db->anydirty = 0;
- }
- *ptr = db->data[XFORM (addr)];
- return ok;
-}
-
-/* Writeback any dirty lines to the remote. */
-static int
-dcache_writeback (dcache)
- DCACHE *dcache;
-{
- struct dcache_block *db;
-
- db = dcache->valid_head;
-
- while (db)
- {
- if (!dcache_write_line (dcache, db))
- return 0;
- db = db->p;
- }
- return 1;
-}
-
-
-/* Using the data cache DCACHE return the contents of the word at
- address ADDR in the remote machine. */
-int
-dcache_fetch (dcache, addr)
- DCACHE *dcache;
- CORE_ADDR addr;
-{
- int res;
-
- if (dcache_xfer_memory (dcache, addr, (char *)&res, sizeof res, 0) != sizeof res)
- memory_error (EIO, addr);
-
- return res;
-}
-
-
-/* Write the byte at PTR into ADDR in the data cache.
- Return zero on write error.
- */
-
-static int
-dcache_poke_byte (dcache, addr, ptr)
- DCACHE *dcache;
- CORE_ADDR addr;
- char *ptr;
-{
- register struct dcache_block *db = dcache_hit (dcache, addr);
-
- if (!db)
- {
- db = dcache_alloc (dcache);
- db->addr = MASK (addr);
- memset (db->state, ENTRY_BAD, sizeof (db->data));
- }
-
- db->data[XFORM (addr)] = *ptr;
- db->state[XFORM (addr)] = ENTRY_DIRTY;
- db->anydirty = 1;
- return 1;
-}
-
-/* Write the word at ADDR both in the data cache and in the remote machine.
- Return zero on write error.
- */
-
-int
-dcache_poke (dcache, addr, data)
- DCACHE *dcache;
- CORE_ADDR addr;
- int data;
-{
- if (dcache_xfer_memory (dcache, addr, (char *)&data, sizeof data, 1) != sizeof data)
- return 0;
-
- return dcache_writeback (dcache);
-}
-
-
-/* Initialize the data cache. */
-DCACHE *
-dcache_init (reading, writing)
- memxferfunc reading;
- memxferfunc writing;
-{
- int csize = sizeof (struct dcache_block) * DCACHE_SIZE;
- DCACHE *dcache;
-
- dcache = (DCACHE *) xmalloc (sizeof (*dcache));
- dcache->read_memory = reading;
- dcache->write_memory = writing;
-
- dcache->the_cache = (struct dcache_block *) xmalloc (csize);
- memset (dcache->the_cache, 0, csize);
-
- dcache_flush (dcache);
-
- last_cache = dcache;
- return 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.
-
- Returns length of data written or read; 0 for error.
-
- This routine is indended to be called by remote_xfer_ functions. */
-
-int
-dcache_xfer_memory (dcache, memaddr, myaddr, len, should_write)
- DCACHE *dcache;
- CORE_ADDR memaddr;
- char *myaddr;
- int len;
- int should_write;
-{
- int i;
-
- if (remote_dcache)
- {
- int (*xfunc) PARAMS ((DCACHE *dcache, CORE_ADDR addr, char *ptr));
- xfunc = should_write ? dcache_poke_byte : dcache_peek_byte;
-
- for (i = 0; i < len; i++)
- {
- if (!xfunc (dcache, memaddr + i, myaddr + i))
- return 0;
- }
- dcache->cache_has_stuff = 1;
- dcache_writeback (dcache);
- }
- else
- {
- memxferfunc xfunc;
- xfunc = should_write ? dcache->write_memory : dcache->read_memory;
-
- if (dcache->cache_has_stuff)
- dcache_flush (dcache);
-
- len = xfunc (memaddr, myaddr, len);
- }
- return len;
-}
-
-static void
-dcache_info (exp, tty)
- char *exp;
- int tty;
-{
- struct dcache_block *p;
-
- if (!remote_dcache)
- {
- printf_filtered ("Dcache not enabled\n");
- return;
- }
- printf_filtered ("Dcache enabled, line width %d, depth %d\n",
- LINE_SIZE, DCACHE_SIZE);
-
- printf_filtered ("Cache state:\n");
-
- for (p = last_cache->valid_head; p; p = p->p)
- {
- int j;
- printf_filtered ("Line at %08xd, referenced %d times\n",
- p->addr, p->refs);
-
- for (j = 0; j < LINE_SIZE; j++)
- printf_filtered ("%02x", p->data[j] & 0xFF);
- printf_filtered ("\n");
-
- for (j = 0; j < LINE_SIZE; j++)
- printf_filtered (" %2x", p->state[j]);
- printf_filtered ("\n");
- }
-}
-
-void
-_initialize_dcache ()
-{
- add_show_from_set
- (add_set_cmd ("remotecache", class_support, var_boolean,
- (char *) &remote_dcache,
- "\
-Set cache use for remote targets.\n\
-When on, use data caching for remote targets. For many remote targets\n\
-this option can offer better throughput for reading target memory.\n\
-Unfortunately, gdb does not currently know anything about volatile\n\
-registers and thus data caching will produce incorrect results with\n\
-volatile registers are in use. By default, this option is on.",
- &setlist),
- &showlist);
-
- add_info ("dcache", dcache_info,
- "Print information on the dcache performance.");
-
-}