1 /* Caching code for GDB, the GNU debugger.
3 Copyright (C) 1992, 1993, 1995, 1996, 1998, 1999, 2000, 2001, 2003, 2007
4 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 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., 51 Franklin Street, Fifth Floor,
21 Boston, MA 02110-1301, 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 res
= target_write (¤t_target
, TARGET_OBJECT_RAW_MEMORY
,
306 NULL
, myaddr
, memaddr
, dirty_len
);
310 memset (&db
->state
[XFORM(memaddr
)], ENTRY_OK
, res
);
321 /* Read cache line */
323 dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
)
330 struct mem_region
*region
;
332 /* If there are any dirty bytes in the line, it must be written
333 before a new line can be read */
336 if (!dcache_write_line (dcache
, db
))
346 region
= lookup_mem_region(memaddr
);
347 if (memaddr
+ len
< region
->hi
)
350 reg_len
= region
->hi
- memaddr
;
352 if (!region
->attrib
.cache
|| region
->attrib
.mode
== MEM_WO
)
360 res
= target_read (¤t_target
, TARGET_OBJECT_RAW_MEMORY
,
361 NULL
, myaddr
, memaddr
, reg_len
);
370 memset (db
->state
, ENTRY_OK
, sizeof (db
->data
));
376 /* Get a free cache block, put or keep it on the valid list,
377 and return its address. */
379 static struct dcache_block
*
380 dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
)
382 struct dcache_block
*db
;
384 /* Take something from the free list */
385 db
= dcache
->free_head
;
388 dcache
->free_head
= db
->p
;
392 /* Nothing left on free list, so grab one from the valid list */
393 db
= dcache
->valid_head
;
395 if (!dcache_write_line (dcache
, db
))
398 dcache
->valid_head
= db
->p
;
401 db
->addr
= MASK(addr
);
404 memset (db
->state
, ENTRY_BAD
, sizeof (db
->data
));
406 /* append this line to end of valid list */
407 if (!dcache
->valid_head
)
408 dcache
->valid_head
= db
;
410 dcache
->valid_tail
->p
= db
;
411 dcache
->valid_tail
= db
;
417 /* Writeback any dirty lines. */
419 dcache_writeback (DCACHE
*dcache
)
421 struct dcache_block
*db
;
423 db
= dcache
->valid_head
;
427 if (!dcache_write_line (dcache
, db
))
435 /* Using the data cache DCACHE return the contents of the byte at
436 address ADDR in the remote machine.
438 Returns 0 on error. */
441 dcache_peek_byte (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
)
443 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
447 db
= dcache_alloc (dcache
, addr
);
452 if (db
->state
[XFORM (addr
)] == ENTRY_BAD
)
454 if (!dcache_read_line(dcache
, db
))
458 *ptr
= db
->data
[XFORM (addr
)];
463 /* Write the byte at PTR into ADDR in the data cache.
464 Return zero on write error.
468 dcache_poke_byte (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
)
470 struct dcache_block
*db
= dcache_hit (dcache
, addr
);
474 db
= dcache_alloc (dcache
, addr
);
479 db
->data
[XFORM (addr
)] = *ptr
;
480 db
->state
[XFORM (addr
)] = ENTRY_DIRTY
;
485 /* Initialize the data cache. */
489 int csize
= sizeof (struct dcache_block
) * DCACHE_SIZE
;
492 dcache
= (DCACHE
*) xmalloc (sizeof (*dcache
));
494 dcache
->the_cache
= (struct dcache_block
*) xmalloc (csize
);
495 memset (dcache
->the_cache
, 0, csize
);
497 dcache_invalidate (dcache
);
503 /* Free a data cache */
505 dcache_free (DCACHE
*dcache
)
507 if (last_cache
== dcache
)
510 xfree (dcache
->the_cache
);
514 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
515 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
518 Returns length of data written or read; 0 for error.
520 This routine is indended to be called by remote_xfer_ functions. */
523 dcache_xfer_memory (DCACHE
*dcache
, CORE_ADDR memaddr
, gdb_byte
*myaddr
,
524 int len
, int should_write
)
527 int (*xfunc
) (DCACHE
*dcache
, CORE_ADDR addr
, gdb_byte
*ptr
);
528 xfunc
= should_write
? dcache_poke_byte
: dcache_peek_byte
;
530 for (i
= 0; i
< len
; i
++)
532 if (!xfunc (dcache
, memaddr
+ i
, myaddr
+ i
))
536 /* FIXME: There may be some benefit from moving the cache writeback
537 to a higher layer, as it could occur after a sequence of smaller
538 writes have been completed (as when a stack frame is constructed
539 for an inferior function call). Note that only moving it up one
540 level to target_xfer_memory() (also target_xfer_memory_partial())
541 is not sufficent, since we want to coalesce memory transfers that
542 are "logically" connected but not actually a single call to one
543 of the memory transfer functions. */
546 dcache_writeback (dcache
);
552 dcache_info (char *exp
, int tty
)
554 struct dcache_block
*p
;
556 printf_filtered (_("Dcache line width %d, depth %d\n"),
557 LINE_SIZE
, DCACHE_SIZE
);
561 printf_filtered (_("Cache state:\n"));
563 for (p
= last_cache
->valid_head
; p
; p
= p
->p
)
566 printf_filtered (_("Line at %s, referenced %d times\n"),
567 paddr (p
->addr
), p
->refs
);
569 for (j
= 0; j
< LINE_SIZE
; j
++)
570 printf_filtered ("%02x", p
->data
[j
] & 0xFF);
571 printf_filtered (("\n"));
573 for (j
= 0; j
< LINE_SIZE
; j
++)
574 printf_filtered ("%2x", p
->state
[j
]);
575 printf_filtered ("\n");
581 _initialize_dcache (void)
583 add_setshow_boolean_cmd ("remotecache", class_support
,
584 &dcache_enabled_p
, _("\
585 Set cache use for remote targets."), _("\
586 Show cache use for remote targets."), _("\
587 When on, use data caching for remote targets. For many remote targets\n\
588 this option can offer better throughput for reading target memory.\n\
589 Unfortunately, gdb does not currently know anything about volatile\n\
590 registers and thus data caching will produce incorrect results with\n\
591 volatile registers are in use. By default, this option is off."),
593 show_dcache_enabled_p
,
594 &setlist
, &showlist
);
596 add_info ("dcache", dcache_info
,
597 _("Print information on the dcache performance."));
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