coregrind/m_execontext.c

/*--------------------------------------------------------------------*/
/*--- Store and compare stack backtraces            m_execontext.c ---*/
/*--------------------------------------------------------------------*/

/*
   This file is part of Valgrind, a dynamic binary instrumentation
   framework.

   Copyright (C) 2000-2007 Julian Seward 
      jseward@acm.org

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307, USA.

   The GNU General Public License is contained in the file COPYING.
*/

#include "pub_core_basics.h"
#include "pub_core_debuglog.h"
#include "pub_core_execontext.h"    // self
#include "pub_core_libcassert.h"
#include "pub_core_libcprint.h"     // For VG_(message)()
#include "pub_core_mallocfree.h"
#include "pub_core_options.h"
#include "pub_core_stacktrace.h"

/*------------------------------------------------------------*/
/*--- Low-level ExeContext storage.                        ---*/
/*------------------------------------------------------------*/

/* The first 4 IP values are used in comparisons to remove duplicate
   errors, and for comparing against suppression specifications.  The
   rest are purely informational (but often important).

   The contexts are stored in a traditional chained hash table, so as
   to allow quick determination of whether a new context already
   exists.  The hash table starts small and expands dynamically, so as
   to keep the load factor below 1.0.

   The idea is only to ever store any one context once, so as to save
   space and make exact comparisons faster. */


/* Primes for the hash table */

#define N_EC_PRIMES 18

static SizeT ec_primes[N_EC_PRIMES] = {
         769UL,         1543UL,         3079UL,          6151UL,
       12289UL,        24593UL,        49157UL,         98317UL,
      196613UL,       393241UL,       786433UL,       1572869UL,
     3145739UL,      6291469UL,     12582917UL,      25165843UL,
    50331653UL,    100663319UL
};


/* Each element is present in a hash chain, and also contains a
   variable length array of guest code addresses (the useful part). */

struct _ExeContext {
   struct _ExeContext* chain;
   UInt   n_ips;
   /* Variable-length array.  The size is 'n_ips'; at
      least 1, at most VG_DEEPEST_BACKTRACE.  [0] is the current IP,
      [1] is its caller, [2] is the caller of [1], etc. */
   Addr ips[0];
};


/* This is the dynamically expanding hash table. */
static ExeContext** ec_htab; /* array [ec_htab_size] of ExeContext* */
static SizeT        ec_htab_size;     /* one of the values in ec_primes */
static SizeT        ec_htab_size_idx; /* 0 .. N_EC_PRIMES-1 */


/* Stats only: the number of times the system was searched to locate a
   context. */
static ULong ec_searchreqs;

/* Stats only: the number of full context comparisons done. */
static ULong ec_searchcmps;

/* Stats only: total number of stored contexts. */
static ULong ec_totstored;

/* Number of 2, 4 and (fast) full cmps done. */
static ULong ec_cmp2s;
static ULong ec_cmp4s;
static ULong ec_cmpAlls;


/*------------------------------------------------------------*/
/*--- Exported functions.                                  ---*/
/*------------------------------------------------------------*/


/* Initialise this subsystem. */
static void init_ExeContext_storage ( void )
{
   Int i;
   static Bool init_done = False;
   if (init_done)
      return;
   ec_searchreqs = 0;
   ec_searchcmps = 0;
   ec_totstored = 0;
   ec_cmp2s = 0;
   ec_cmp4s = 0;
   ec_cmpAlls = 0;

   ec_htab_size_idx = 0;
   ec_htab_size = ec_primes[ec_htab_size_idx];
   ec_htab = VG_(arena_malloc)(VG_AR_EXECTXT, 
                               sizeof(ExeContext*) * ec_htab_size);
   for (i = 0; i < ec_htab_size; i++)
      ec_htab[i] = NULL;

   init_done = True;
}


/* Print stats. */
void VG_(print_ExeContext_stats) ( void )
{
   init_ExeContext_storage();
   VG_(message)(Vg_DebugMsg, 
      "   exectx: %,lu lists, %,llu contexts (avg %,llu per list)",
      ec_htab_size, ec_totstored, ec_totstored / ec_htab_size
   );
   VG_(message)(Vg_DebugMsg, 
      "   exectx: %,llu searches, %,llu full compares (%,llu per 1000)",
      ec_searchreqs, ec_searchcmps, 
      ec_searchreqs == 0 
         ? 0L 
         : ( (ec_searchcmps * 1000) / ec_searchreqs ) 
   );
   VG_(message)(Vg_DebugMsg, 
      "   exectx: %,llu cmp2, %,llu cmp4, %,llu cmpAll",
      ec_cmp2s, ec_cmp4s, ec_cmpAlls 
   );
}


/* Print an ExeContext. */
void VG_(pp_ExeContext) ( ExeContext* ec )
{
   VG_(pp_StackTrace)( ec->ips, ec->n_ips );
}


/* Compare two ExeContexts, comparing all callers. */
Bool VG_(eq_ExeContext) ( VgRes res, ExeContext* e1, ExeContext* e2 )
{
   Int i;

   if (e1 == NULL || e2 == NULL) 
      return False;

   // Must be at least one address in each trace.
   tl_assert(e1->n_ips >= 1 && e2->n_ips >= 1);

   switch (res) {
   case Vg_LowRes:
      /* Just compare the top two callers. */
      ec_cmp2s++;
      for (i = 0; i < 2; i++) {
         if ( (e1->n_ips <= i) &&  (e2->n_ips <= i)) return True;
         if ( (e1->n_ips <= i) && !(e2->n_ips <= i)) return False;
         if (!(e1->n_ips <= i) &&  (e2->n_ips <= i)) return False;
         if (e1->ips[i] != e2->ips[i])               return False;
      }
      return True;

   case Vg_MedRes:
      /* Just compare the top four callers. */
      ec_cmp4s++;
      for (i = 0; i < 4; i++) {
         if ( (e1->n_ips <= i) &&  (e2->n_ips <= i)) return True;
         if ( (e1->n_ips <= i) && !(e2->n_ips <= i)) return False;
         if (!(e1->n_ips <= i) &&  (e2->n_ips <= i)) return False;
         if (e1->ips[i] != e2->ips[i])               return False;
      }
      return True;

   case Vg_HighRes:
      ec_cmpAlls++;
      /* Compare them all -- just do pointer comparison. */
      if (e1 != e2) return False;
      return True;

   default:
      VG_(core_panic)("VG_(eq_ExeContext): unrecognised VgRes");
   }
}

/* VG_(record_ExeContext) is the head honcho here.  Take a snapshot of
   the client's stack.  Search our collection of ExeContexts to see if
   we already have it, and if not, allocate a new one.  Either way,
   return a pointer to the context.  If there is a matching context we
   guarantee to not allocate a new one.  Thus we never store
   duplicates, and so exact equality can be quickly done as equality
   on the returned ExeContext* values themselves.  Inspired by Hugs's
   Text type.

   Also checks whether the hash table needs expanding, and expands it
   if so. */

static inline UWord ROLW ( UWord w, Int n )
{
   Int bpw = 8 * sizeof(UWord);
   w = (w << n) | (w >> (bpw-n));
   return w;
}

static UWord calc_hash ( Addr* ips, UInt n_ips, UWord htab_sz )
{
   UInt  i;
   UWord hash = 0;
   vg_assert(htab_sz > 0);
   for (i = 0; i < n_ips; i++) {
      hash ^= ips[i];
      hash = ROLW(hash, 19);
   }
   return hash % htab_sz;
}

static void resize_ec_htab ( void )
{
   SizeT        i;
   SizeT        new_size;
   ExeContext** new_ec_htab;

   vg_assert(ec_htab_size_idx >= 0 && ec_htab_size_idx < N_EC_PRIMES);
   if (ec_htab_size_idx == N_EC_PRIMES-1)
      return; /* out of primes - can't resize further */

   new_size = ec_primes[ec_htab_size_idx + 1];
   new_ec_htab = VG_(arena_malloc)(VG_AR_EXECTXT,
                                   sizeof(ExeContext*) * new_size);

   VG_(debugLog)(
      1, "execontext",
         "resizing htab from size %lu to %lu (idx %lu)  Total#ECs=%llu\n",
         ec_htab_size, new_size, ec_htab_size_idx + 1, ec_totstored);

   for (i = 0; i < new_size; i++)
      new_ec_htab[i] = NULL;

   for (i = 0; i < ec_htab_size; i++) {
      ExeContext* cur = ec_htab[i];
      while (cur) {
         ExeContext* next = cur->chain;
         UWord hash = calc_hash(cur->ips, cur->n_ips, new_size);
         vg_assert(hash < new_size);
         cur->chain = new_ec_htab[hash];
         new_ec_htab[hash] = cur;
         cur = next;
      }
   }

   VG_(arena_free)(VG_AR_EXECTXT, ec_htab);
   ec_htab      = new_ec_htab;
   ec_htab_size = new_size;
   ec_htab_size_idx++;
}

ExeContext* VG_(record_ExeContext) ( ThreadId tid, Word first_ip_delta )
{
   Int         i;
   Addr        ips[VG_DEEPEST_BACKTRACE];
   Bool        same;
   UWord       hash;
   ExeContext* new_ec;
   ExeContext* list;
   UInt        n_ips;
   ExeContext  *prev2, *prev;

   static UInt ctr = 0;

   vg_assert(sizeof(void*) == sizeof(UWord));
   vg_assert(sizeof(void*) == sizeof(Addr));

   init_ExeContext_storage();
   vg_assert(VG_(clo_backtrace_size) >= 1 &&
             VG_(clo_backtrace_size) <= VG_DEEPEST_BACKTRACE);

   n_ips = VG_(get_StackTrace)( tid, ips, VG_(clo_backtrace_size),
                                first_ip_delta );
   tl_assert(n_ips >= 1 && n_ips <= VG_(clo_backtrace_size));

   /* Now figure out if we've seen this one before.  First hash it so
      as to determine the list number. */
   hash = calc_hash( ips, n_ips, ec_htab_size );

   /* And (the expensive bit) look a for matching entry in the list. */

   ec_searchreqs++;

   prev2 = NULL;
   prev  = NULL;
   list  = ec_htab[hash];

   while (True) {
      if (list == NULL) break;
      ec_searchcmps++;
      same = True;
      for (i = 0; i < n_ips; i++) {
         if (list->ips[i] != ips[i]) {
            same = False;
            break; 
         }
      }
      if (same) break;
      prev2 = prev;
      prev  = list;
      list  = list->chain;
   }

   if (list != NULL) {
      /* Yay!  We found it.  Once every 8 searches, move it one step
         closer to the start of the list to make future searches
         cheaper. */
      if (0 == ((ctr++) & 7)) {
         if (prev2 != NULL && prev != NULL) {
            /* Found at 3rd or later position in the chain. */
            vg_assert(prev2->chain == prev);
            vg_assert(prev->chain  == list);
            prev2->chain = list;
            prev->chain  = list->chain;
            list->chain  = prev;
         }
         else if (prev2 == NULL && prev != NULL) {
            /* Found at 2nd position in the chain. */
            vg_assert(ec_htab[hash] == prev);
            vg_assert(prev->chain == list);
            prev->chain = list->chain;
            list->chain = prev;
            ec_htab[hash] = list;
         }
      }
      return list;
   }

   /* Bummer.  We have to allocate a new context record. */
   ec_totstored++;

   new_ec = VG_(arena_malloc)( VG_AR_EXECTXT, 
                               sizeof(struct _ExeContext) 
                               + n_ips * sizeof(Addr) );

   for (i = 0; i < n_ips; i++)
      new_ec->ips[i] = ips[i];

   new_ec->n_ips = n_ips;
   new_ec->chain = ec_htab[hash];
   ec_htab[hash] = new_ec;

   /* Resize the hash table, maybe? */
   if ( ((ULong)ec_totstored) > ((ULong)ec_htab_size) ) {
      vg_assert(ec_htab_size_idx >= 0 && ec_htab_size_idx < N_EC_PRIMES);
      if (ec_htab_size_idx < N_EC_PRIMES-1)
         resize_ec_htab();
   }

   return new_ec;
}

StackTrace VG_(extract_StackTrace) ( ExeContext* e )
{                                  
   return e->ips;
}  

/*--------------------------------------------------------------------*/
/*--- end                                           m_execontext.c ---*/
/*--------------------------------------------------------------------*/