1 /* Caching code for GDB, the GNU debugger.
3 Copyright 1992, 1993, 1995, 1996, 1998, 1999, 2000, 2001, 2003 Free
4 Software Foundation, Inc.
6 This file is part of GDB.
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.
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.
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,
21 Boston, MA 02111-1307, USA. */
26 #include "gdb_string.h"
30 /* The data cache could lead to incorrect results because it doesn't
31 know about volatile variables, thus making it impossible to debug
32 functions which use memory mapped I/O devices. Set the nocache
33 memory region attribute in those cases.
35 In general the dcache speeds up performance, some speed improvement
36 comes from the actual caching mechanism, but the major gain is in
37 the reduction of the remote protocol overhead; instead of reading
38 or writing a large area of memory in 4 byte requests, the cache
39 bundles up the requests into 32 byte (actually LINE_SIZE) chunks.
40 Reducing the overhead to an eighth of what it was. This is very
41 obvious when displaying a large amount of data,
46 ----------------------------
47 first time | 4 sec 2 sec improvement due to chunking
48 second time | 4 sec 0 sec improvement due to caching
50 The cache structure is unusual, we keep a number of cache blocks
51 (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
52 Within each line we remember the address of the line (always a
53 multiple of the LINE_SIZE) and a vector of bytes over the range.
54 There's another vector which contains the state of the bytes.
56 ENTRY_BAD means that the byte is just plain wrong, and has no
57 correspondence with anything else (as it would when the cache is
58 turned on, but nothing has been done to it.
60 ENTRY_DIRTY means that the byte has some data in it which should be
61 written out to the remote target one day, but contains correct
64 ENTRY_OK means that the data is the same in the cache as it is in
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.
81 /* NOTE: Interaction of dcache and memory region attributes
83 As there is no requirement that memory region attributes be aligned
84 to or be a multiple of the dcache page size, dcache_read_line() and
85 dcache_write_line() must break up the page by memory region. If a
86 chunk does not have the cache attribute set, an invalid memory type
87 is set, etc., then the chunk is skipped. Those chunks are handled
88 in target_xfer_memory() (or target_xfer_memory_partial()).
90 This doesn't occur very often. The most common occurance is when
91 the last bit of the .text segment and the first bit of the .data
92 segment fall within the same dcache page with a ro/cacheable memory
93 region defined for the .text segment and a rw/non-cacheable memory
94 region defined for the .data segment. */
96 /* This value regulates the number of cache blocks stored.
97 Smaller values reduce the time spent searching for a cache
98 line, and reduce memory requirements, but increase the risk
99 of a line not being in memory */
101 #define DCACHE_SIZE 64
103 /* This value regulates the size of a cache line. Smaller values
104 reduce the time taken to read a single byte, but reduce overall
107 #define LINE_SIZE_POWER (5)
108 #define LINE_SIZE (1 << LINE_SIZE_POWER)
110 /* Each cache block holds LINE_SIZE bytes of data
111 starting at a multiple-of-LINE_SIZE address. */
113 #define LINE_SIZE_MASK ((LINE_SIZE - 1))
114 #define XFORM(x) ((x) & LINE_SIZE_MASK)
115 #define MASK(x) ((x) & ~LINE_SIZE_MASK)
118 #define ENTRY_BAD 0 /* data at this byte is wrong */
119 #define ENTRY_DIRTY 1 /* data at this byte needs to be written back */
120 #define ENTRY_OK 2 /* data at this byte is same as in memory */
125 struct dcache_block
*p
; /* next in list */
126 CORE_ADDR addr
; /* Address for which data is recorded. */
127 char data
[LINE_SIZE
]; /* bytes at given address */
128 unsigned char state
[LINE_SIZE
]; /* what state the data is in */
130 /* whether anything in state is dirty - used to speed up the
138 /* FIXME: dcache_struct used to have a cache_has_stuff field that was
139 used to record whether the cache had been accessed. This was used
140 to invalidate the cache whenever caching was (re-)enabled (if the
141 cache was disabled and later re-enabled, it could contain stale
142 data). This was not needed because the cache is write through and
143 the code that enables, disables, and deletes memory region all
144 invalidate the cache.
146 This is overkill, since it also invalidates cache lines from
147 unrelated regions. One way this could be addressed by adding a
148 new function that takes an address and a length and invalidates
149 only those cache lines that match. */
154 struct dcache_block
*free_head
;
155 struct dcache_block
*free_tail
;
158 struct dcache_block
*valid_head
;
159 struct dcache_block
*valid_tail
;
161 /* The cache itself. */
162 struct dcache_block
*the_cache
;
165 static int dcache_poke_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
);
167 static int dcache_peek_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
);
169 static struct dcache_block
*dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
);
171 static int dcache_write_line (DCACHE
*dcache
, struct dcache_block
*db
);
173 static int dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
);
175 static struct dcache_block
*dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
);
177 static int dcache_writeback (DCACHE
*dcache
);
179 static void dcache_info (char *exp
, int tty
);
181 void _initialize_dcache (void);
183 static int dcache_enabled_p
= 0;
185 DCACHE
*last_cache
; /* Used by info dcache */
188 /* Free all the data cache blocks, thus discarding all cached data. */
191 dcache_invalidate (DCACHE
*dcache
)
194 dcache
->valid_head
= 0;
195 dcache
->valid_tail
= 0;
197 dcache
->free_head
= 0;
198 dcache
->free_tail
= 0;
200 for (i
= 0; i
< DCACHE_SIZE
; i
++)
202 struct dcache_block
*db
= dcache
->the_cache
+ i
;
204 if (!dcache
->free_head
)
205 dcache
->free_head
= db
;
207 dcache
->free_tail
->p
= db
;
208 dcache
->free_tail
= db
;
215 /* If addr is present in the dcache, return the address of the block
218 static struct dcache_block
*
219 dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
)
221 struct dcache_block
*db
;
223 /* Search all cache blocks for one that is at this address. */
224 db
= dcache
->valid_head
;
228 if (MASK (addr
) == db
->addr
)
239 /* Make sure that anything in this line which needs to
243 dcache_write_line (DCACHE
*dcache
, struct dcache_block
*db
)
250 struct mem_region
*region
;
265 region
= lookup_mem_region(memaddr
);
266 if (memaddr
+ len
< region
->hi
)
269 reg_len
= region
->hi
- memaddr
;
271 if (!region
->attrib
.cache
|| region
->attrib
.mode
== MEM_RO
)
282 while (reg_len
> 0) {
283 if (db
->state
[s
] == ENTRY_DIRTY
)
294 while (reg_len
> 0) {
295 if (db
->state
[e
] != ENTRY_DIRTY
)
302 while (dirty_len
> 0)
304 res
= do_xfer_memory(memaddr
, myaddr
, dirty_len
, 1,
309 memset (&db
->state
[XFORM(memaddr
)], ENTRY_OK
, res
);
322 /* Read cache line */
324 dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
)
331 struct mem_region
*region
;
333 /* If there are any dirty bytes in the line, it must be written
334 before a new line can be read */
337 if (!dcache_write_line (dcache
, db
))
347 region
= lookup_mem_region(memaddr
);
348 if (memaddr
+ len
< region
->hi
)
351 reg_len
= region
->hi
- memaddr
;
353 if (!region
->attrib
.cache
|| region
->attrib
.mode
== MEM_WO
)
363 res
= do_xfer_memory (memaddr
, myaddr
, reg_len
, 0,
375 memset (db
->state
, ENTRY_OK
, sizeof (db
->data
));
381 /* Get a free cache block, put or keep it on the valid list,
382 and return its address. */
384 static struct dcache_block
*
385 dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
)
387 struct dcache_block
*db
;
389 /* Take something from the free list */
390 db
= dcache
->free_head
;
393 dcache
->free_head
= db
->p
;
397 /* Nothing left on free list, so grab one from the valid list */
398 db
= dcache
->valid_head
;
400 if (!dcache_write_line (dcache
, db
))
403 dcache
->valid_head
= db
->p
;
406 db
->addr
= MASK(addr
);
409 memset (db
->state
, ENTRY_BAD
, sizeof (db
->data
));
411 /* append this line to end of valid list */
412 if (!dcache
->valid_head
)
413 dcache
->valid_head
= db
;
415 dcache
->valid_tail
->p
= db
;
416 dcache
->valid_tail
= db
;
422 /* Writeback any dirty lines. */
424 dcache_writeback (DCACHE
*dcache
)
426 struct dcache_block
*db
;
428 db
= dcache
->valid_head
;
432 if (!dcache_write_line (dcache
, db
))
440 /* Using the data cache DCACHE return the contents of the byte at
441 address ADDR in the remote machine.
443 Returns 0 on error. */
446 dcache_peek_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
)
448 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
452 db
= dcache_alloc (dcache
, addr
);
457 if (db
->state
[XFORM (addr
)] == ENTRY_BAD
)
459 if (!dcache_read_line(dcache
, db
))
463 *ptr
= db
->data
[XFORM (addr
)];
468 /* Write the byte at PTR into ADDR in the data cache.
469 Return zero on write error.
473 dcache_poke_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
)
475 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
479 db
= dcache_alloc (dcache
, addr
);
484 db
->data
[XFORM (addr
)] = *ptr
;
485 db
->state
[XFORM (addr
)] = ENTRY_DIRTY
;
490 /* Initialize the data cache. */
494 int csize
= sizeof (struct dcache_block
) * DCACHE_SIZE
;
497 dcache
= (DCACHE
*) xmalloc (sizeof (*dcache
));
499 dcache
->the_cache
= (struct dcache_block
*) xmalloc (csize
);
500 memset (dcache
->the_cache
, 0, csize
);
502 dcache_invalidate (dcache
);
508 /* Free a data cache */
510 dcache_free (DCACHE
*dcache
)
512 if (last_cache
== dcache
)
515 xfree (dcache
->the_cache
);
519 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
520 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
523 Returns length of data written or read; 0 for error.
525 This routine is indended to be called by remote_xfer_ functions. */
528 dcache_xfer_memory (DCACHE
*dcache
, CORE_ADDR memaddr
, char *myaddr
, int len
,
532 int (*xfunc
) (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
);
533 xfunc
= should_write
? dcache_poke_byte
: dcache_peek_byte
;
535 for (i
= 0; i
< len
; i
++)
537 if (!xfunc (dcache
, memaddr
+ i
, myaddr
+ i
))
541 /* FIXME: There may be some benefit from moving the cache writeback
542 to a higher layer, as it could occur after a sequence of smaller
543 writes have been completed (as when a stack frame is constructed
544 for an inferior function call). Note that only moving it up one
545 level to target_xfer_memory() (also target_xfer_memory_partial())
546 is not sufficent, since we want to coalesce memory transfers that
547 are "logically" connected but not actually a single call to one
548 of the memory transfer functions. */
551 dcache_writeback (dcache
);
557 dcache_info (char *exp
, int tty
)
559 struct dcache_block
*p
;
561 printf_filtered ("Dcache line width %d, depth %d\n",
562 LINE_SIZE
, DCACHE_SIZE
);
566 printf_filtered ("Cache state:\n");
568 for (p
= last_cache
->valid_head
; p
; p
= p
->p
)
571 printf_filtered ("Line at %s, referenced %d times\n",
572 paddr (p
->addr
), p
->refs
);
574 for (j
= 0; j
< LINE_SIZE
; j
++)
575 printf_filtered ("%02x", p
->data
[j
] & 0xFF);
576 printf_filtered ("\n");
578 for (j
= 0; j
< LINE_SIZE
; j
++)
579 printf_filtered ("%2x", p
->state
[j
]);
580 printf_filtered ("\n");
586 _initialize_dcache (void)
589 (add_set_cmd ("remotecache", class_support
, var_boolean
,
590 (char *) &dcache_enabled_p
,
592 Set cache use for remote targets.\n\
593 When on, use data caching for remote targets. For many remote targets\n\
594 this option can offer better throughput for reading target memory.\n\
595 Unfortunately, gdb does not currently know anything about volatile\n\
596 registers and thus data caching will produce incorrect results with\n\
597 volatile registers are in use. By default, this option is off.",
601 add_info ("dcache", dcache_info
,
602 "Print information on the dcache performance.");
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