m_execontext.c revision 31513b4ab8477029517f07f0dcf1b441cb818548 
1
2/*--------------------------------------------------------------------*/
3/*--- Store and compare stack backtraces            m_execontext.c ---*/
4/*--------------------------------------------------------------------*/
5
6/*
7   This file is part of Valgrind, a dynamic binary instrumentation
8   framework.
9
10   Copyright (C) 2000-2005 Julian Seward
11      jseward@acm.org
12
13   This program is free software; you can redistribute it and/or
14   modify it under the terms of the GNU General Public License as
15   published by the Free Software Foundation; either version 2 of the
16   License, or (at your option) any later version.
17
18   This program is distributed in the hope that it will be useful, but
19   WITHOUT ANY WARRANTY; without even the implied warranty of
20   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
21   General Public License for more details.
22
23   You should have received a copy of the GNU General Public License
24   along with this program; if not, write to the Free Software
25   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
26   02111-1307, USA.
27
28   The GNU General Public License is contained in the file COPYING.
29*/
30
31#include "core.h"
32#include "pub_core_execontext.h"
33#include "pub_core_options.h"
34#include "pub_core_profile.h"
35
36/*------------------------------------------------------------*/
37/*--- Low-level ExeContext storage.                        ---*/
38/*------------------------------------------------------------*/
39
40/* The first 4 IP values are used in comparisons do remove duplicate errors,
41   and for comparing against suppression specifications.  The rest are
42   purely informational (but often important). */
43
44struct _ExeContext {
45   struct _ExeContext * next;
46   /* Variable-length array.  The size is VG_(clo_backtrace_size); at
47      least 1, at most VG_DEEPEST_BACKTRACE.  [0] is the current IP,
48      [1] is its caller, [2] is the caller of [1], etc. */
49   Addr ips[0];
50};
51
52/* Number of lists in which we keep track of ExeContexts.  Should be
53   prime. */
54#define N_EC_LISTS 4999 /* a prime number */
55
56/* The idea is only to ever store any one context once, so as to save
57   space and make exact comparisons faster. */
58
59static ExeContext* ec_list[N_EC_LISTS];
60
61/* Stats only: the number of times the system was searched to locate a
62   context. */
63static UInt ec_searchreqs;
64
65/* Stats only: the number of full context comparisons done. */
66static UInt ec_searchcmps;
67
68/* Stats only: total number of stored contexts. */
69static UInt ec_totstored;
70
71/* Number of 2, 4 and (fast) full cmps done. */
72static UInt ec_cmp2s;
73static UInt ec_cmp4s;
74static UInt ec_cmpAlls;
75
76
77/*------------------------------------------------------------*/
78/*--- Exported functions.                                  ---*/
79/*------------------------------------------------------------*/
80
81
82/* Initialise this subsystem. */
83static void init_ExeContext_storage ( void )
84{
85   Int i;
86   static Bool init_done = False;
87   if (init_done)
88      return;
89   ec_searchreqs = 0;
90   ec_searchcmps = 0;
91   ec_totstored = 0;
92   ec_cmp2s = 0;
93   ec_cmp4s = 0;
94   ec_cmpAlls = 0;
95   for (i = 0; i < N_EC_LISTS; i++)
96      ec_list[i] = NULL;
97   init_done = True;
98}
99
100
101/* Print stats. */
102void VG_(print_ExeContext_stats) ( void )
103{
104   init_ExeContext_storage();
105   VG_(message)(Vg_DebugMsg,
106      "   exectx: %d lists, %d contexts (avg %d per list)",
107      N_EC_LISTS, ec_totstored,
108      ec_totstored / N_EC_LISTS
109   );
110   VG_(message)(Vg_DebugMsg,
111      "   exectx: %d searches, %d full compares (%d per 1000)",
112      ec_searchreqs, ec_searchcmps,
113      ec_searchreqs == 0
114         ? 0
115         : (UInt)( (((ULong)ec_searchcmps) * 1000)
116           / ((ULong)ec_searchreqs ))
117   );
118   VG_(message)(Vg_DebugMsg,
119      "   exectx: %d cmp2, %d cmp4, %d cmpAll",
120      ec_cmp2s, ec_cmp4s, ec_cmpAlls
121   );
122}
123
124
125/* Print an ExeContext. */
126void VG_(pp_ExeContext) ( ExeContext* ec )
127{
128   VG_(pp_StackTrace)( ec->ips, VG_(clo_backtrace_size) );
129}
130
131
132/* Compare two ExeContexts, comparing all callers. */
133Bool VG_(eq_ExeContext) ( VgRes res, ExeContext* e1, ExeContext* e2 )
134{
135   if (e1 == NULL || e2 == NULL)
136      return False;
137   switch (res) {
138   case Vg_LowRes:
139      /* Just compare the top two callers. */
140      ec_cmp2s++;
141      if (e1->ips[0] != e2->ips[0]) return False;
142
143      if (VG_(clo_backtrace_size) < 2) return True;
144      if (e1->ips[1] != e2->ips[1]) return False;
145      return True;
146
147   case Vg_MedRes:
148      /* Just compare the top four callers. */
149      ec_cmp4s++;
150      if (e1->ips[0] != e2->ips[0]) return False;
151
152      if (VG_(clo_backtrace_size) < 2) return True;
153      if (e1->ips[1] != e2->ips[1]) return False;
154
155      if (VG_(clo_backtrace_size) < 3) return True;
156      if (e1->ips[2] != e2->ips[2]) return False;
157
158      if (VG_(clo_backtrace_size) < 4) return True;
159      if (e1->ips[3] != e2->ips[3]) return False;
160      return True;
161
162   case Vg_HighRes:
163      ec_cmpAlls++;
164      /* Compare them all -- just do pointer comparison. */
165      if (e1 != e2) return False;
166      return True;
167
168   default:
169      VG_(core_panic)("VG_(eq_ExeContext): unrecognised VgRes");
170   }
171}
172
173/* This guy is the head honcho here.  Take a snapshot of the client's
174   stack.  Search our collection of ExeContexts to see if we already
175   have it, and if not, allocate a new one.  Either way, return a
176   pointer to the context.  If there is a matching context we
177   guarantee to not allocate a new one.  Thus we never store
178   duplicates, and so exact equality can be quickly done as equality
179   on the returned ExeContext* values themselves.  Inspired by Hugs's
180   Text type.
181*/
182ExeContext* VG_(record_ExeContext) ( ThreadId tid )
183{
184   Int         i;
185   Addr        ips[VG_DEEPEST_BACKTRACE];
186   Bool        same;
187   UWord       hash;
188   ExeContext* new_ec;
189   ExeContext* list;
190
191   VGP_PUSHCC(VgpExeContext);
192
193   init_ExeContext_storage();
194   vg_assert(VG_(clo_backtrace_size) >= 1
195             && VG_(clo_backtrace_size) <= VG_DEEPEST_BACKTRACE);
196
197   VG_(get_StackTrace)( tid, ips, VG_(clo_backtrace_size) );
198
199   /* Now figure out if we've seen this one before.  First hash it so
200      as to determine the list number. */
201
202   hash = 0;
203   for (i = 0; i < VG_(clo_backtrace_size); i++) {
204      hash ^= ips[i];
205      hash = (hash << 29) | (hash >> 3);
206   }
207   hash = hash % N_EC_LISTS;
208
209   /* And (the expensive bit) look a matching entry in the list. */
210
211   ec_searchreqs++;
212
213   list = ec_list[hash];
214
215   while (True) {
216      if (list == NULL) break;
217      ec_searchcmps++;
218      same = True;
219      for (i = 0; i < VG_(clo_backtrace_size); i++) {
220         if (list->ips[i] != ips[i]) {
221            same = False;
222            break;
223         }
224      }
225      if (same) break;
226      list = list->next;
227   }
228
229   if (list != NULL) {
230      /* Yay!  We found it.  */
231      VGP_POPCC(VgpExeContext);
232      return list;
233   }
234
235   /* Bummer.  We have to allocate a new context record. */
236   ec_totstored++;
237
238   new_ec = VG_(arena_malloc)( VG_AR_EXECTXT,
239                               sizeof(struct _ExeContext *)
240                               + VG_(clo_backtrace_size) * sizeof(Addr) );
241
242   for (i = 0; i < VG_(clo_backtrace_size); i++)
243      new_ec->ips[i] = ips[i];
244
245   new_ec->next = ec_list[hash];
246   ec_list[hash] = new_ec;
247
248   VGP_POPCC(VgpExeContext);
249   return new_ec;
250}
251
252StackTrace VG_(extract_StackTrace) ( ExeContext* e )
253{
254   return e->ips;
255}
256
257/*--------------------------------------------------------------------*/
258/*--- end                                           m_execontext.c ---*/
259/*--------------------------------------------------------------------*/
260