m_execontext.c revision 2024234c590f408994b373abfb00bc2cd2a90c48 
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
35/*------------------------------------------------------------*/
36/*--- Low-level ExeContext storage.                        ---*/
37/*------------------------------------------------------------*/
38
39/* The first 4 IP values are used in comparisons do remove duplicate errors,
40   and for comparing against suppression specifications.  The rest are
41   purely informational (but often important). */
42
43struct _ExeContext {
44   struct _ExeContext * next;
45   /* Variable-length array.  The size is VG_(clo_backtrace_size); at
46      least 1, at most VG_DEEPEST_BACKTRACE.  [0] is the current IP,
47      [1] is its caller, [2] is the caller of [1], etc. */
48   Addr ips[0];
49};
50
51/* Number of lists in which we keep track of ExeContexts.  Should be
52   prime. */
53#define N_EC_LISTS 4999 /* a prime number */
54
55/* The idea is only to ever store any one context once, so as to save
56   space and make exact comparisons faster. */
57
58static ExeContext* ec_list[N_EC_LISTS];
59
60/* Stats only: the number of times the system was searched to locate a
61   context. */
62static UInt ec_searchreqs;
63
64/* Stats only: the number of full context comparisons done. */
65static UInt ec_searchcmps;
66
67/* Stats only: total number of stored contexts. */
68static UInt ec_totstored;
69
70/* Number of 2, 4 and (fast) full cmps done. */
71static UInt ec_cmp2s;
72static UInt ec_cmp4s;
73static UInt ec_cmpAlls;
74
75
76/*------------------------------------------------------------*/
77/*--- Exported functions.                                  ---*/
78/*------------------------------------------------------------*/
79
80
81/* Initialise this subsystem. */
82static void init_ExeContext_storage ( void )
83{
84   Int i;
85   static Bool init_done = False;
86   if (init_done)
87      return;
88   ec_searchreqs = 0;
89   ec_searchcmps = 0;
90   ec_totstored = 0;
91   ec_cmp2s = 0;
92   ec_cmp4s = 0;
93   ec_cmpAlls = 0;
94   for (i = 0; i < N_EC_LISTS; i++)
95      ec_list[i] = NULL;
96   init_done = True;
97}
98
99
100/* Print stats. */
101void VG_(print_ExeContext_stats) ( void )
102{
103   init_ExeContext_storage();
104   VG_(message)(Vg_DebugMsg,
105      "   exectx: %d lists, %d contexts (avg %d per list)",
106      N_EC_LISTS, ec_totstored,
107      ec_totstored / N_EC_LISTS
108   );
109   VG_(message)(Vg_DebugMsg,
110      "   exectx: %d searches, %d full compares (%d per 1000)",
111      ec_searchreqs, ec_searchcmps,
112      ec_searchreqs == 0
113         ? 0
114         : (UInt)( (((ULong)ec_searchcmps) * 1000)
115           / ((ULong)ec_searchreqs ))
116   );
117   VG_(message)(Vg_DebugMsg,
118      "   exectx: %d cmp2, %d cmp4, %d cmpAll",
119      ec_cmp2s, ec_cmp4s, ec_cmpAlls
120   );
121}
122
123
124/* Print an ExeContext. */
125void VG_(pp_ExeContext) ( ExeContext* ec )
126{
127   VG_(pp_StackTrace)( ec->ips, VG_(clo_backtrace_size) );
128}
129
130
131/* Compare two ExeContexts, comparing all callers. */
132Bool VG_(eq_ExeContext) ( VgRes res, ExeContext* e1, ExeContext* e2 )
133{
134   if (e1 == NULL || e2 == NULL)
135      return False;
136   switch (res) {
137   case Vg_LowRes:
138      /* Just compare the top two callers. */
139      ec_cmp2s++;
140      if (e1->ips[0] != e2->ips[0]) return False;
141
142      if (VG_(clo_backtrace_size) < 2) return True;
143      if (e1->ips[1] != e2->ips[1]) return False;
144      return True;
145
146   case Vg_MedRes:
147      /* Just compare the top four callers. */
148      ec_cmp4s++;
149      if (e1->ips[0] != e2->ips[0]) return False;
150
151      if (VG_(clo_backtrace_size) < 2) return True;
152      if (e1->ips[1] != e2->ips[1]) return False;
153
154      if (VG_(clo_backtrace_size) < 3) return True;
155      if (e1->ips[2] != e2->ips[2]) return False;
156
157      if (VG_(clo_backtrace_size) < 4) return True;
158      if (e1->ips[3] != e2->ips[3]) return False;
159      return True;
160
161   case Vg_HighRes:
162      ec_cmpAlls++;
163      /* Compare them all -- just do pointer comparison. */
164      if (e1 != e2) return False;
165      return True;
166
167   default:
168      VG_(core_panic)("VG_(eq_ExeContext): unrecognised VgRes");
169   }
170}
171
172/* This guy is the head honcho here.  Take a snapshot of the client's
173   stack.  Search our collection of ExeContexts to see if we already
174   have it, and if not, allocate a new one.  Either way, return a
175   pointer to the context.  If there is a matching context we
176   guarantee to not allocate a new one.  Thus we never store
177   duplicates, and so exact equality can be quickly done as equality
178   on the returned ExeContext* values themselves.  Inspired by Hugs's
179   Text type.
180*/
181ExeContext* VG_(record_ExeContext) ( ThreadId tid )
182{
183   Int         i;
184   Addr        ips[VG_DEEPEST_BACKTRACE];
185   Bool        same;
186   UWord       hash;
187   ExeContext* new_ec;
188   ExeContext* list;
189
190   VGP_PUSHCC(VgpExeContext);
191
192   init_ExeContext_storage();
193   vg_assert(VG_(clo_backtrace_size) >= 1
194             && VG_(clo_backtrace_size) <= VG_DEEPEST_BACKTRACE);
195
196   VG_(get_StackTrace)( tid, ips, VG_(clo_backtrace_size) );
197
198   /* Now figure out if we've seen this one before.  First hash it so
199      as to determine the list number. */
200
201   hash = 0;
202   for (i = 0; i < VG_(clo_backtrace_size); i++) {
203      hash ^= ips[i];
204      hash = (hash << 29) | (hash >> 3);
205   }
206   hash = hash % N_EC_LISTS;
207
208   /* And (the expensive bit) look a matching entry in the list. */
209
210   ec_searchreqs++;
211
212   list = ec_list[hash];
213
214   while (True) {
215      if (list == NULL) break;
216      ec_searchcmps++;
217      same = True;
218      for (i = 0; i < VG_(clo_backtrace_size); i++) {
219         if (list->ips[i] != ips[i]) {
220            same = False;
221            break;
222         }
223      }
224      if (same) break;
225      list = list->next;
226   }
227
228   if (list != NULL) {
229      /* Yay!  We found it.  */
230      VGP_POPCC(VgpExeContext);
231      return list;
232   }
233
234   /* Bummer.  We have to allocate a new context record. */
235   ec_totstored++;
236
237   new_ec = VG_(arena_malloc)( VG_AR_EXECTXT,
238                               sizeof(struct _ExeContext *)
239                               + VG_(clo_backtrace_size) * sizeof(Addr) );
240
241   for (i = 0; i < VG_(clo_backtrace_size); i++)
242      new_ec->ips[i] = ips[i];
243
244   new_ec->next = ec_list[hash];
245   ec_list[hash] = new_ec;
246
247   VGP_POPCC(VgpExeContext);
248   return new_ec;
249}
250
251StackTrace VG_(extract_StackTrace) ( ExeContext* e )
252{
253   return e->ips;
254}
255
256/*--------------------------------------------------------------------*/
257/*--- end                                           m_execontext.c ---*/
258/*--------------------------------------------------------------------*/
259