1 /* Caching code for GDB, the GNU debugger.
3 Copyright (C) 1992, 1993, 1995, 1996, 1998, 1999, 2000, 2001, 2003, 2007,
4 2008 Free 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 3 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, see <http://www.gnu.org/licenses/>. */
24 #include "gdb_string.h"
28 /* The data cache could lead to incorrect results because it doesn't
29 know about volatile variables, thus making it impossible to debug
30 functions which use memory mapped I/O devices. Set the nocache
31 memory region attribute in those cases.
33 In general the dcache speeds up performance, some speed improvement
34 comes from the actual caching mechanism, but the major gain is in
35 the reduction of the remote protocol overhead; instead of reading
36 or writing a large area of memory in 4 byte requests, the cache
37 bundles up the requests into 32 byte (actually LINE_SIZE) chunks.
38 Reducing the overhead to an eighth of what it was. This is very
39 obvious when displaying a large amount of data,
44 ----------------------------
45 first time | 4 sec 2 sec improvement due to chunking
46 second time | 4 sec 0 sec improvement due to caching
48 The cache structure is unusual, we keep a number of cache blocks
49 (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
50 Within each line we remember the address of the line (always a
51 multiple of the LINE_SIZE) and a vector of bytes over the range.
52 There's another vector which contains the state of the bytes.
54 ENTRY_BAD means that the byte is just plain wrong, and has no
55 correspondence with anything else (as it would when the cache is
56 turned on, but nothing has been done to it.
58 ENTRY_DIRTY means that the byte has some data in it which should be
59 written out to the remote target one day, but contains correct
62 ENTRY_OK means that the data is the same in the cache as it is in
66 The ENTRY_DIRTY state is necessary because GDB likes to write large
67 lumps of memory in small bits. If the caching mechanism didn't
68 maintain the DIRTY information, then something like a two byte
69 write would mean that the entire cache line would have to be read,
70 the two bytes modified and then written out again. The alternative
71 would be to not read in the cache line in the first place, and just
72 write the two bytes directly into target memory. The trouble with
73 that is that it really nails performance, because of the remote
74 protocol overhead. This way, all those little writes are bundled
75 up into an entire cache line write in one go, without having to
76 read the cache line in the first place.
79 /* NOTE: Interaction of dcache and memory region attributes
81 As there is no requirement that memory region attributes be aligned
82 to or be a multiple of the dcache page size, dcache_read_line() and
83 dcache_write_line() must break up the page by memory region. If a
84 chunk does not have the cache attribute set, an invalid memory type
85 is set, etc., then the chunk is skipped. Those chunks are handled
86 in target_xfer_memory() (or target_xfer_memory_partial()).
88 This doesn't occur very often. The most common occurance is when
89 the last bit of the .text segment and the first bit of the .data
90 segment fall within the same dcache page with a ro/cacheable memory
91 region defined for the .text segment and a rw/non-cacheable memory
92 region defined for the .data segment. */
94 /* This value regulates the number of cache blocks stored.
95 Smaller values reduce the time spent searching for a cache
96 line, and reduce memory requirements, but increase the risk
97 of a line not being in memory */
99 #define DCACHE_SIZE 64
101 /* This value regulates the size of a cache line. Smaller values
102 reduce the time taken to read a single byte, but reduce overall
105 #define LINE_SIZE_POWER (5)
106 #define LINE_SIZE (1 << LINE_SIZE_POWER)
108 /* Each cache block holds LINE_SIZE bytes of data
109 starting at a multiple-of-LINE_SIZE address. */
111 #define LINE_SIZE_MASK ((LINE_SIZE - 1))
112 #define XFORM(x) ((x) & LINE_SIZE_MASK)
113 #define MASK(x) ((x) & ~LINE_SIZE_MASK)
116 #define ENTRY_BAD 0 /* data at this byte is wrong */
117 #define ENTRY_DIRTY 1 /* data at this byte needs to be written back */
118 #define ENTRY_OK 2 /* data at this byte is same as in memory */
123 struct dcache_block
*p
; /* next in list */
124 CORE_ADDR addr
; /* Address for which data is recorded. */
125 gdb_byte data
[LINE_SIZE
]; /* bytes at given address */
126 unsigned char state
[LINE_SIZE
]; /* what state the data is in */
128 /* whether anything in state is dirty - used to speed up the
136 /* FIXME: dcache_struct used to have a cache_has_stuff field that was
137 used to record whether the cache had been accessed. This was used
138 to invalidate the cache whenever caching was (re-)enabled (if the
139 cache was disabled and later re-enabled, it could contain stale
140 data). This was not needed because the cache is write through and
141 the code that enables, disables, and deletes memory region all
142 invalidate the cache.
144 This is overkill, since it also invalidates cache lines from
145 unrelated regions. One way this could be addressed by adding a
146 new function that takes an address and a length and invalidates
147 only those cache lines that match. */
152 struct dcache_block
*free_head
;
153 struct dcache_block
*free_tail
;
156 struct dcache_block
*valid_head
;
157 struct dcache_block
*valid_tail
;
159 /* The cache itself. */
160 struct dcache_block
*the_cache
;
163 static struct dcache_block
*dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
);
165 static int dcache_write_line (DCACHE
*dcache
, struct dcache_block
*db
);
167 static int dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
);
169 static struct dcache_block
*dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
);
171 static int dcache_writeback (DCACHE
*dcache
);
173 static void dcache_info (char *exp
, int tty
);
175 void _initialize_dcache (void);
177 static int dcache_enabled_p
= 0;
179 show_dcache_enabled_p (struct ui_file
*file
, int from_tty
,
180 struct cmd_list_element
*c
, const char *value
)
182 fprintf_filtered (file
, _("Cache use for remote targets is %s.\n"), value
);
186 DCACHE
*last_cache
; /* Used by info dcache */
189 /* Free all the data cache blocks, thus discarding all cached data. */
192 dcache_invalidate (DCACHE
*dcache
)
195 dcache
->valid_head
= 0;
196 dcache
->valid_tail
= 0;
198 dcache
->free_head
= 0;
199 dcache
->free_tail
= 0;
201 for (i
= 0; i
< DCACHE_SIZE
; i
++)
203 struct dcache_block
*db
= dcache
->the_cache
+ i
;
205 if (!dcache
->free_head
)
206 dcache
->free_head
= db
;
208 dcache
->free_tail
->p
= db
;
209 dcache
->free_tail
= db
;
216 /* If addr is present in the dcache, return the address of the block
219 static struct dcache_block
*
220 dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
)
222 struct dcache_block
*db
;
224 /* Search all cache blocks for one that is at this address. */
225 db
= dcache
->valid_head
;
229 if (MASK (addr
) == db
->addr
)
240 /* Make sure that anything in this line which needs to
244 dcache_write_line (DCACHE
*dcache
, struct dcache_block
*db
)
251 struct mem_region
*region
;
266 region
= lookup_mem_region(memaddr
);
267 if (memaddr
+ len
< region
->hi
)
270 reg_len
= region
->hi
- memaddr
;
272 if (!region
->attrib
.cache
|| region
->attrib
.mode
== MEM_RO
)
283 while (reg_len
> 0) {
284 if (db
->state
[s
] == ENTRY_DIRTY
)
295 while (reg_len
> 0) {
296 if (db
->state
[e
] != ENTRY_DIRTY
)
303 res
= target_write (¤t_target
, TARGET_OBJECT_RAW_MEMORY
,
304 NULL
, myaddr
, memaddr
, dirty_len
);
308 memset (&db
->state
[XFORM(memaddr
)], ENTRY_OK
, res
);
319 /* Read cache line */
321 dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
)
328 struct mem_region
*region
;
330 /* If there are any dirty bytes in the line, it must be written
331 before a new line can be read */
334 if (!dcache_write_line (dcache
, db
))
344 region
= lookup_mem_region(memaddr
);
345 if (memaddr
+ len
< region
->hi
)
348 reg_len
= region
->hi
- memaddr
;
350 if (!region
->attrib
.cache
|| region
->attrib
.mode
== MEM_WO
)
358 res
= target_read (¤t_target
, TARGET_OBJECT_RAW_MEMORY
,
359 NULL
, myaddr
, memaddr
, reg_len
);
368 memset (db
->state
, ENTRY_OK
, sizeof (db
->data
));
374 /* Get a free cache block, put or keep it on the valid list,
375 and return its address. */
377 static struct dcache_block
*
378 dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
)
380 struct dcache_block
*db
;
382 /* Take something from the free list */
383 db
= dcache
->free_head
;
386 dcache
->free_head
= db
->p
;
390 /* Nothing left on free list, so grab one from the valid list */
391 db
= dcache
->valid_head
;
393 if (!dcache_write_line (dcache
, db
))
396 dcache
->valid_head
= db
->p
;
399 db
->addr
= MASK(addr
);
402 memset (db
->state
, ENTRY_BAD
, sizeof (db
->data
));
404 /* append this line to end of valid list */
405 if (!dcache
->valid_head
)
406 dcache
->valid_head
= db
;
408 dcache
->valid_tail
->p
= db
;
409 dcache
->valid_tail
= db
;
415 /* Writeback any dirty lines. */
417 dcache_writeback (DCACHE
*dcache
)
419 struct dcache_block
*db
;
421 db
= dcache
->valid_head
;
425 if (!dcache_write_line (dcache
, db
))
433 /* Using the data cache DCACHE return the contents of the byte at
434 address ADDR in the remote machine.
436 Returns 0 on error. */
439 dcache_peek_byte (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
)
441 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
445 db
= dcache_alloc (dcache
, addr
);
450 if (db
->state
[XFORM (addr
)] == ENTRY_BAD
)
452 if (!dcache_read_line(dcache
, db
))
456 *ptr
= db
->data
[XFORM (addr
)];
461 /* Write the byte at PTR into ADDR in the data cache.
462 Return zero on write error.
466 dcache_poke_byte (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
)
468 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
472 db
= dcache_alloc (dcache
, addr
);
477 db
->data
[XFORM (addr
)] = *ptr
;
478 db
->state
[XFORM (addr
)] = ENTRY_DIRTY
;
483 /* Initialize the data cache. */
487 int csize
= sizeof (struct dcache_block
) * DCACHE_SIZE
;
490 dcache
= (DCACHE
*) xmalloc (sizeof (*dcache
));
492 dcache
->the_cache
= (struct dcache_block
*) xmalloc (csize
);
493 memset (dcache
->the_cache
, 0, csize
);
495 dcache_invalidate (dcache
);
501 /* Free a data cache */
503 dcache_free (DCACHE
*dcache
)
505 if (last_cache
== dcache
)
508 xfree (dcache
->the_cache
);
512 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
513 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
516 Returns length of data written or read; 0 for error.
518 This routine is indended to be called by remote_xfer_ functions. */
521 dcache_xfer_memory (DCACHE
*dcache
, CORE_ADDR memaddr
, gdb_byte
*myaddr
,
522 int len
, int should_write
)
525 int (*xfunc
) (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
);
526 xfunc
= should_write
? dcache_poke_byte
: dcache_peek_byte
;
528 for (i
= 0; i
< len
; i
++)
530 if (!xfunc (dcache
, memaddr
+ i
, myaddr
+ i
))
534 /* FIXME: There may be some benefit from moving the cache writeback
535 to a higher layer, as it could occur after a sequence of smaller
536 writes have been completed (as when a stack frame is constructed
537 for an inferior function call). Note that only moving it up one
538 level to target_xfer_memory() (also target_xfer_memory_partial())
539 is not sufficent, since we want to coalesce memory transfers that
540 are "logically" connected but not actually a single call to one
541 of the memory transfer functions. */
544 dcache_writeback (dcache
);
550 dcache_info (char *exp
, int tty
)
552 struct dcache_block
*p
;
554 printf_filtered (_("Dcache line width %d, depth %d\n"),
555 LINE_SIZE
, DCACHE_SIZE
);
559 printf_filtered (_("Cache state:\n"));
561 for (p
= last_cache
->valid_head
; p
; p
= p
->p
)
564 printf_filtered (_("Line at %s, referenced %d times\n"),
565 paddr (p
->addr
), p
->refs
);
567 for (j
= 0; j
< LINE_SIZE
; j
++)
568 printf_filtered ("%02x", p
->data
[j
] & 0xFF);
569 printf_filtered (("\n"));
571 for (j
= 0; j
< LINE_SIZE
; j
++)
572 printf_filtered ("%2x", p
->state
[j
]);
573 printf_filtered ("\n");
579 _initialize_dcache (void)
581 add_setshow_boolean_cmd ("remotecache", class_support
,
582 &dcache_enabled_p
, _("\
583 Set cache use for remote targets."), _("\
584 Show cache use for remote targets."), _("\
585 When on, use data caching for remote targets. For many remote targets\n\
586 this option can offer better throughput for reading target memory.\n\
587 Unfortunately, gdb does not currently know anything about volatile\n\
588 registers and thus data caching will produce incorrect results with\n\
589 volatile registers are in use. By default, this option is off."),
591 show_dcache_enabled_p
,
592 &setlist
, &showlist
);
594 add_info ("dcache", dcache_info
,
595 _("Print information on the dcache performance."));
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