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 gdb_byte 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 struct dcache_block
*dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
);
167 static int dcache_write_line (DCACHE
*dcache
, struct dcache_block
*db
);
169 static int dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
);
171 static struct dcache_block
*dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
);
173 static int dcache_writeback (DCACHE
*dcache
);
175 static void dcache_info (char *exp
, int tty
);
177 void _initialize_dcache (void);
179 static int dcache_enabled_p
= 0;
181 show_dcache_enabled_p (struct ui_file
*file
, int from_tty
,
182 struct cmd_list_element
*c
, const char *value
)
184 fprintf_filtered (file
, _("Cache use for remote targets is %s.\n"), value
);
188 DCACHE
*last_cache
; /* Used by info dcache */
191 /* Free all the data cache blocks, thus discarding all cached data. */
194 dcache_invalidate (DCACHE
*dcache
)
197 dcache
->valid_head
= 0;
198 dcache
->valid_tail
= 0;
200 dcache
->free_head
= 0;
201 dcache
->free_tail
= 0;
203 for (i
= 0; i
< DCACHE_SIZE
; i
++)
205 struct dcache_block
*db
= dcache
->the_cache
+ i
;
207 if (!dcache
->free_head
)
208 dcache
->free_head
= db
;
210 dcache
->free_tail
->p
= db
;
211 dcache
->free_tail
= db
;
218 /* If addr is present in the dcache, return the address of the block
221 static struct dcache_block
*
222 dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
)
224 struct dcache_block
*db
;
226 /* Search all cache blocks for one that is at this address. */
227 db
= dcache
->valid_head
;
231 if (MASK (addr
) == db
->addr
)
242 /* Make sure that anything in this line which needs to
246 dcache_write_line (DCACHE
*dcache
, struct dcache_block
*db
)
253 struct mem_region
*region
;
268 region
= lookup_mem_region(memaddr
);
269 if (memaddr
+ len
< region
->hi
)
272 reg_len
= region
->hi
- memaddr
;
274 if (!region
->attrib
.cache
|| region
->attrib
.mode
== MEM_RO
)
285 while (reg_len
> 0) {
286 if (db
->state
[s
] == ENTRY_DIRTY
)
297 while (reg_len
> 0) {
298 if (db
->state
[e
] != ENTRY_DIRTY
)
305 while (dirty_len
> 0)
307 res
= do_xfer_memory(memaddr
, myaddr
, dirty_len
, 1,
312 memset (&db
->state
[XFORM(memaddr
)], ENTRY_OK
, res
);
325 /* Read cache line */
327 dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
)
334 struct mem_region
*region
;
336 /* If there are any dirty bytes in the line, it must be written
337 before a new line can be read */
340 if (!dcache_write_line (dcache
, db
))
350 region
= lookup_mem_region(memaddr
);
351 if (memaddr
+ len
< region
->hi
)
354 reg_len
= region
->hi
- memaddr
;
356 if (!region
->attrib
.cache
|| region
->attrib
.mode
== MEM_WO
)
366 res
= do_xfer_memory (memaddr
, myaddr
, reg_len
, 0,
378 memset (db
->state
, ENTRY_OK
, sizeof (db
->data
));
384 /* Get a free cache block, put or keep it on the valid list,
385 and return its address. */
387 static struct dcache_block
*
388 dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
)
390 struct dcache_block
*db
;
392 /* Take something from the free list */
393 db
= dcache
->free_head
;
396 dcache
->free_head
= db
->p
;
400 /* Nothing left on free list, so grab one from the valid list */
401 db
= dcache
->valid_head
;
403 if (!dcache_write_line (dcache
, db
))
406 dcache
->valid_head
= db
->p
;
409 db
->addr
= MASK(addr
);
412 memset (db
->state
, ENTRY_BAD
, sizeof (db
->data
));
414 /* append this line to end of valid list */
415 if (!dcache
->valid_head
)
416 dcache
->valid_head
= db
;
418 dcache
->valid_tail
->p
= db
;
419 dcache
->valid_tail
= db
;
425 /* Writeback any dirty lines. */
427 dcache_writeback (DCACHE
*dcache
)
429 struct dcache_block
*db
;
431 db
= dcache
->valid_head
;
435 if (!dcache_write_line (dcache
, db
))
443 /* Using the data cache DCACHE return the contents of the byte at
444 address ADDR in the remote machine.
446 Returns 0 on error. */
449 dcache_peek_byte (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
)
451 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
455 db
= dcache_alloc (dcache
, addr
);
460 if (db
->state
[XFORM (addr
)] == ENTRY_BAD
)
462 if (!dcache_read_line(dcache
, db
))
466 *ptr
= db
->data
[XFORM (addr
)];
471 /* Write the byte at PTR into ADDR in the data cache.
472 Return zero on write error.
476 dcache_poke_byte (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
)
478 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
482 db
= dcache_alloc (dcache
, addr
);
487 db
->data
[XFORM (addr
)] = *ptr
;
488 db
->state
[XFORM (addr
)] = ENTRY_DIRTY
;
493 /* Initialize the data cache. */
497 int csize
= sizeof (struct dcache_block
) * DCACHE_SIZE
;
500 dcache
= (DCACHE
*) xmalloc (sizeof (*dcache
));
502 dcache
->the_cache
= (struct dcache_block
*) xmalloc (csize
);
503 memset (dcache
->the_cache
, 0, csize
);
505 dcache_invalidate (dcache
);
511 /* Free a data cache */
513 dcache_free (DCACHE
*dcache
)
515 if (last_cache
== dcache
)
518 xfree (dcache
->the_cache
);
522 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
523 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
526 Returns length of data written or read; 0 for error.
528 This routine is indended to be called by remote_xfer_ functions. */
531 dcache_xfer_memory (DCACHE
*dcache
, CORE_ADDR memaddr
, gdb_byte
*myaddr
,
532 int len
, int should_write
)
535 int (*xfunc
) (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
);
536 xfunc
= should_write
? dcache_poke_byte
: dcache_peek_byte
;
538 for (i
= 0; i
< len
; i
++)
540 if (!xfunc (dcache
, memaddr
+ i
, myaddr
+ i
))
544 /* FIXME: There may be some benefit from moving the cache writeback
545 to a higher layer, as it could occur after a sequence of smaller
546 writes have been completed (as when a stack frame is constructed
547 for an inferior function call). Note that only moving it up one
548 level to target_xfer_memory() (also target_xfer_memory_partial())
549 is not sufficent, since we want to coalesce memory transfers that
550 are "logically" connected but not actually a single call to one
551 of the memory transfer functions. */
554 dcache_writeback (dcache
);
560 dcache_info (char *exp
, int tty
)
562 struct dcache_block
*p
;
564 printf_filtered (_("Dcache line width %d, depth %d\n"),
565 LINE_SIZE
, DCACHE_SIZE
);
569 printf_filtered (_("Cache state:\n"));
571 for (p
= last_cache
->valid_head
; p
; p
= p
->p
)
574 printf_filtered (_("Line at %s, referenced %d times\n"),
575 paddr (p
->addr
), p
->refs
);
577 for (j
= 0; j
< LINE_SIZE
; j
++)
578 printf_filtered ("%02x", p
->data
[j
] & 0xFF);
579 printf_filtered (("\n"));
581 for (j
= 0; j
< LINE_SIZE
; j
++)
582 printf_filtered ("%2x", p
->state
[j
]);
583 printf_filtered ("\n");
589 _initialize_dcache (void)
591 add_setshow_boolean_cmd ("remotecache", class_support
,
592 &dcache_enabled_p
, _("\
593 Set cache use for remote targets."), _("\
594 Show cache use for remote targets."), _("\
595 When on, use data caching for remote targets. For many remote targets\n\
596 this option can offer better throughput for reading target memory.\n\
597 Unfortunately, gdb does not currently know anything about volatile\n\
598 registers and thus data caching will produce incorrect results with\n\
599 volatile registers are in use. By default, this option is off."),
601 show_dcache_enabled_p
,
602 &setlist
, &showlist
);
604 add_info ("dcache", dcache_info
,
605 _("Print information on the dcache performance."));
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