coregrind/vg_errcontext.c

/*--------------------------------------------------------------------*/
/*--- Management of error messages.                vg_errcontext.c ---*/
/*--------------------------------------------------------------------*/

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

   Copyright (C) 2000-2004 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 "core.h"

/*------------------------------------------------------------*/
/*--- Globals                                              ---*/
/*------------------------------------------------------------*/

/* The list of error contexts found, both suppressed and unsuppressed.
   Initially empty, and grows as errors are detected. */
static Error* vg_errors = NULL;

/* The list of suppression directives, as read from the specified
   suppressions file. */
static Supp* vg_suppressions = NULL;

/* Running count of unsuppressed errors detected. */
static UInt n_errs_found = 0;

/* Running count of suppressed errors detected. */
static UInt n_errs_suppressed = 0;

/* forwards ... */
static Supp* is_suppressible_error ( Error* err );


/*------------------------------------------------------------*/
/*--- Error type                                           ---*/
/*------------------------------------------------------------*/

/* Note: it is imperative this doesn't overlap with (0..) at all, as tools
 * effectively extend it by defining their own enums in the (0..) range. */
typedef
   enum { 
      PThreadErr      = -1,   // Pthreading error
   }
   CoreErrorKind;

/* Errors.  Extensible (via the 'extra' field).  Tools can use a normal
   enum (with element values in the normal range (0..)) for `ekind'. 
   Functions for getting/setting the tool-relevant fields are in
   include/tool.h.

   When errors are found and recorded with VG_(maybe_record_error)(), all
   the tool must do is pass in the four parameters;  core will
   allocate/initialise the error record.
*/
struct _Error {
   struct _Error* next;
   // NULL if unsuppressed; or ptr to suppression record.
   Supp* supp;
   Int count;
   ThreadId tid;

   // The tool-specific part
   ExeContext* where;      // Initialised by core
   Int ekind;              // Used by ALL.  Must be in the range (0..)
   Addr addr;              // Used frequently
   Char* string;           // Used frequently
   void* extra;            // For any tool-specific extras
};

ExeContext* VG_(get_error_where) ( Error* err )
{
   return err->where;
}

ErrorKind VG_(get_error_kind) ( Error* err )
{
   return err->ekind;
}

Addr VG_(get_error_address) ( Error* err )
{
   return err->addr;
}

Char* VG_(get_error_string) ( Error* err )
{
   return err->string;
}

void* VG_(get_error_extra)  ( Error* err )
{
   return err->extra;
}

UInt VG_(get_n_errs_found)( void )
{
   return n_errs_found;
}

/*------------------------------------------------------------*/
/*--- Suppression type                                     ---*/
/*------------------------------------------------------------*/

/* Note: it is imperative this doesn't overlap with (0..) at all, as tools
 * effectively extend it by defining their own enums in the (0..) range. */
typedef
   enum {
      PThreadSupp = -1,    /* Matches PThreadErr */
   }
   CoreSuppKind;

/* For each caller specified for a suppression, record the nature of
   the caller name.  Not of interest to tools. */
typedef
   enum { 
      ObjName,    /* Name is of an shared object file. */
      FunName     /* Name is of a function. */
   }
   SuppLocTy;

/* Suppressions.  Tools can get/set tool-relevant parts with functions
   declared in include/tool.h.  Extensible via the 'extra' field. 
   Tools can use a normal enum (with element values in the normal range
   (0..)) for `skind'. */
struct _Supp {
   struct _Supp* next;
   Int count;     // The number of times this error has been suppressed.
   Char* sname;   // The name by which the suppression is referred to.
   /* First two (name of fn where err occurs, and immediate caller)
    * are mandatory;  extra two are optional. */
   SuppLocTy caller_ty[VG_N_SUPP_CALLERS];
   Char*     caller   [VG_N_SUPP_CALLERS];

   /* The tool-specific part */
   SuppKind skind;   // What kind of suppression.  Must use the range (0..).
   Char* string;     // String -- use is optional.  NULL by default.
   void* extra;      // Anything else -- use is optional.  NULL by default.
};

SuppKind VG_(get_supp_kind) ( Supp* su )
{
   return su->skind;
}

Char* VG_(get_supp_string) ( Supp* su )
{
   return su->string;
}

void* VG_(get_supp_extra)  ( Supp* su )
{
   return su->extra;
}


void VG_(set_supp_kind)   ( Supp* su, SuppKind skind )
{
   su->skind = skind;
}

void VG_(set_supp_string) ( Supp* su, Char* string )
{
   su->string = string;
}

void VG_(set_supp_extra)  ( Supp* su, void* extra )
{
   su->extra = extra;
}


/*------------------------------------------------------------*/
/*--- Helper fns                                           ---*/
/*------------------------------------------------------------*/

/* Compare error contexts, to detect duplicates.  Note that if they
   are otherwise the same, the faulting addrs and associated rwoffsets
   are allowed to be different.  */
static Bool eq_Error ( VgRes res, Error* e1, Error* e2 )
{
   if (e1->ekind != e2->ekind) 
      return False;
   if (!VG_(eq_ExeContext)(res, e1->where, e2->where))
      return False;

   switch (e1->ekind) {
      case PThreadErr:
         vg_assert(VG_(needs).core_errors);
         if (e1->string == e2->string) 
            return True;
         if (0 == VG_(strcmp)(e1->string, e2->string))
            return True;
         return False;
      default: 
         if (VG_(needs).tool_errors)
            return TL_(eq_Error)(res, e1, e2);
         else {
            VG_(printf)("\nUnhandled error type: %u. VG_(needs).tool_errors\n"
                        "probably needs to be set.\n",
                        e1->ekind);
            VG_(tool_panic)("unhandled error type");
         }
   }
}

static void pp_Error ( Error* err, Bool printCount )
{
   if (printCount)
      VG_(message)(Vg_UserMsg, "Observed %d times:", err->count );
   if (err->tid > 1)
      VG_(message)(Vg_UserMsg, "Thread %d:", err->tid );

   switch (err->ekind) {
      case PThreadErr:
         vg_assert(VG_(needs).core_errors);
         VG_(message)(Vg_UserMsg, "%s", err->string );
         VG_(pp_ExeContext)(err->where);
         break;
      default: 
         if (VG_(needs).tool_errors)
            TL_(pp_Error)( err );
         else {
            VG_(printf)("\nUnhandled error type: %u.  VG_(needs).tool_errors\n"
                        "probably needs to be set?\n",
                        err->ekind);
            VG_(tool_panic)("unhandled error type");
         }
   }
}

/* Figure out if we want to perform a given action for this error, possibly
   by asking the user. */
Bool VG_(is_action_requested) ( Char* action, Bool* clo )
{
   Char ch, ch2;
   Int res;

   if (*clo == False)
      return False;

   VG_(message)(Vg_UserMsg, "");

  again:
   VG_(printf)(
      "==%d== "
      "---- %s ? --- [Return/N/n/Y/y/C/c] ---- ", 
      VG_(getpid)(), action
   );

   res = VG_(read)(VG_(clo_input_fd), &ch, 1);
   if (res != 1) goto ioerror;
   /* res == 1 */
   if (ch == '\n') return False;
   if (ch != 'N' && ch != 'n' && ch != 'Y' && ch != 'y' 
      && ch != 'C' && ch != 'c') goto again;

   res = VG_(read)(VG_(clo_input_fd), &ch2, 1);
   if (res != 1) goto ioerror;
   if (ch2 != '\n') goto again;

   /* No, don't want to do action. */
   if (ch == 'n' || ch == 'N') return False;
   /* Yes, want to do action. */
   if (ch == 'y' || ch == 'Y') return True;
   /* No, don't want to do action, and don't ask again either. */
   vg_assert(ch == 'c' || ch == 'C');

  ioerror:
   *clo = False;
   return False;
}


// Initialisation picks out values from the appropriate ThreadState as
// necessary.
static __inline__
void construct_error ( Error* err, ThreadId tid, ErrorKind ekind, Addr a,
                       Char* s, void* extra, ExeContext* where )
{
   tl_assert(tid < VG_N_THREADS);

   /* Core-only parts */
   err->next     = NULL;
   err->supp     = NULL;
   err->count    = 1;
   err->tid      = tid;
   if (NULL == where)
      err->where = VG_(get_ExeContext)( tid );
   else
      err->where = where;

   /* Tool-relevant parts */
   err->ekind  = ekind;
   err->addr   = a;
   err->extra  = extra;
   err->string = s;

   /* sanity... */
   vg_assert( tid < VG_N_THREADS );
}

static void gen_suppression(Error* err)
{
   Int         i;
   static UChar buf[M_VG_ERRTXT];
   Bool        main_done = False;
   ExeContext* ec      = VG_(get_error_where)(err);
   Int         stop_at = VG_(clo_backtrace_size);

   /* At most VG_N_SUPP_CALLERS names */
   if (stop_at > VG_N_SUPP_CALLERS) stop_at = VG_N_SUPP_CALLERS;
   vg_assert(stop_at > 0);

   VG_(printf)("{\n");
   VG_(printf)("   <insert a suppression name here>\n");

   if (PThreadErr == err->ekind) {
      VG_(printf)("   core:PThread\n");

   } else {
      Char* name = TL_(get_error_name)(err);
      if (NULL == name) {
         VG_(message)(Vg_UserMsg, 
                      "(tool does not allow error to be suppressed)");
         return;
      }
      VG_(printf)("   %s:%s\n", VG_(details).name, name);
      TL_(print_extra_suppression_info)(err);
   }

   /* This loop condensed from VG_(mini_stack_dump)() */
   i = 0;
   do {
      Addr eip = ec->ips[i];
      if (i > 0) 
         eip -= MIN_INSTR_SIZE;     // point to calling line
      if ( VG_(get_fnname_nodemangle) (eip, buf,  M_VG_ERRTXT) ) {
         // Stop after "main";  if main() is recursive, stop after last main().

         if ( ! VG_(clo_show_below_main)) {
            if (VG_STREQ(buf, "main"))
               main_done = True;
            else if (main_done)
               break;
         }
         VG_(printf)("   fun:%s\n", buf);
      } else if ( VG_(get_objname)(eip, buf, M_VG_ERRTXT) ) {
         VG_(printf)("   obj:%s\n", buf);
      } else {
         VG_(printf)("   ???:???       "
                     "# unknown, suppression will not work, sorry\n");
      }
      i++;
   } while (i < stop_at && ec->ips[i] != 0);

   VG_(printf)("}\n");
}

static 
void do_actions_on_error(Error* err, Bool allow_db_attach)
{
   Bool still_noisy = True;

   /* Perhaps we want a debugger attach at this point? */
   if (allow_db_attach &&
       VG_(is_action_requested)( "Attach to debugger", & VG_(clo_db_attach) )) 
   {
      VG_(printf)("starting debugger\n");
      VG_(start_debugger)( err->tid );
   }
   /* Or maybe we want to generate the error's suppression? */
   if (VG_(clo_gen_suppressions) == 2
       || (VG_(clo_gen_suppressions) == 1
           && VG_(is_action_requested)( "Print suppression",
                                        &still_noisy ))
      ) {
      gen_suppression(err);
      if (VG_(clo_gen_suppressions) == 1 && !still_noisy)
         VG_(clo_gen_suppressions) = 0;
   }
}

/* Shared between VG_(maybe_record_error)() and VG_(unique_error)(),
   just for pretty printing purposes. */
static Bool is_first_shown_context = True;

/* Top-level entry point to the error management subsystem.
   All detected errors are notified here; this routine decides if/when the
   user should see the error. */
void VG_(maybe_record_error) ( ThreadId tid, 
                               ErrorKind ekind, Addr a, Char* s, void* extra )
{
          Error  err;
          Error* p;
          Error* p_prev;
          UInt   extra_size;
          VgRes  exe_res                = Vg_MedRes;
   static Bool   stopping_message       = False;
   static Bool   slowdown_message       = False;
   static Int    vg_n_errs_shown        = 0;

   /* After M_VG_COLLECT_NO_ERRORS_AFTER_SHOWN different errors have
      been found, or M_VG_COLLECT_NO_ERRORS_AFTER_FOUND total errors
      have been found, just refuse to collect any more.  This stops
      the burden of the error-management system becoming excessive in
      extremely buggy programs, although it does make it pretty
      pointless to continue the Valgrind run after this point. */
   if (VG_(clo_error_limit) 
       && (vg_n_errs_shown >= M_VG_COLLECT_NO_ERRORS_AFTER_SHOWN
           || n_errs_found >= M_VG_COLLECT_NO_ERRORS_AFTER_FOUND)) {
      if (!stopping_message) {
         VG_(message)(Vg_UserMsg, "");

	 if (vg_n_errs_shown >= M_VG_COLLECT_NO_ERRORS_AFTER_SHOWN) {
            VG_(message)(Vg_UserMsg, 
               "More than %d different errors detected.  "
               "I'm not reporting any more.",
               M_VG_COLLECT_NO_ERRORS_AFTER_SHOWN );
         } else {
            VG_(message)(Vg_UserMsg, 
               "More than %d total errors detected.  "
               "I'm not reporting any more.",
               M_VG_COLLECT_NO_ERRORS_AFTER_FOUND );
	 }

         VG_(message)(Vg_UserMsg, 
            "Final error counts will be inaccurate.  Go fix your program!");
         VG_(message)(Vg_UserMsg, 
            "Rerun with --error-limit=no to disable this cutoff.  Note");
         VG_(message)(Vg_UserMsg, 
            "that errors may occur in your program without prior warning from");
         VG_(message)(Vg_UserMsg, 
            "Valgrind, because errors are no longer being displayed.");
         VG_(message)(Vg_UserMsg, "");
         stopping_message = True;
      }
      return;
   }

   /* After M_VG_COLLECT_ERRORS_SLOWLY_AFTER different errors have
      been found, be much more conservative about collecting new
      ones. */
   if (vg_n_errs_shown >= M_VG_COLLECT_ERRORS_SLOWLY_AFTER) {
      exe_res = Vg_LowRes;
      if (!slowdown_message) {
         VG_(message)(Vg_UserMsg, "");
         VG_(message)(Vg_UserMsg, 
            "More than %d errors detected.  Subsequent errors",
            M_VG_COLLECT_ERRORS_SLOWLY_AFTER);
         VG_(message)(Vg_UserMsg, 
            "will still be recorded, but in less detail than before.");
         slowdown_message = True;
      }
   }

   /* Build ourselves the error */
   construct_error ( &err, tid, ekind, a, s, extra, NULL );

   /* First, see if we've got an error record matching this one. */
   p      = vg_errors;
   p_prev = NULL;
   while (p != NULL) {
      if (eq_Error(exe_res, p, &err)) {
         /* Found it. */
         p->count++;
	 if (p->supp != NULL) {
            /* Deal correctly with suppressed errors. */
            p->supp->count++;
            n_errs_suppressed++;	 
         } else {
            n_errs_found++;
         }

         /* Move p to the front of the list so that future searches
            for it are faster. */
         if (p_prev != NULL) {
            vg_assert(p_prev->next == p);
            p_prev->next    = p->next;
            p->next         = vg_errors;
            vg_errors = p;
	 }

         return;
      }
      p_prev = p;
      p      = p->next;
   }

   /* Didn't see it.  Copy and add. */

   /* OK, we're really going to collect it.  The context is on the stack and
      will disappear shortly, so we must copy it.  First do the main
      (non-`extra') part.
     
      Then TL_(update_extra) can update the `extra' part.  This is for when
      there are more details to fill in which take time to work out but
      don't affect our earlier decision to include the error -- by
      postponing those details until now, we avoid the extra work in the
      case where we ignore the error.  Ugly.

      Then, if there is an `extra' part, copy it too, using the size that
      TL_(update_extra) returned.  Also allow for people using the void*
      extra field for a scalar value like an integer.
   */

   /* copy main part */
   p = VG_(arena_malloc)(VG_AR_ERRORS, sizeof(Error));
   *p = err;

   /* update `extra', for non-core errors (core ones don't use 'extra') */
   if (VG_(needs).tool_errors && PThreadErr != ekind) {
      extra_size = TL_(update_extra)(p);

      /* copy block pointed to by `extra', if there is one */
      if (NULL != p->extra && 0 != extra_size) { 
         void* new_extra = VG_(malloc)(extra_size);
         VG_(memcpy)(new_extra, p->extra, extra_size);
         p->extra = new_extra;
      }
   }

   p->next = vg_errors;
   p->supp = is_suppressible_error(&err);
   vg_errors = p;
   if (p->supp == NULL) {
      n_errs_found++;
      if (!is_first_shown_context)
         VG_(message)(Vg_UserMsg, "");
      pp_Error(p, False);
      is_first_shown_context = False;
      vg_n_errs_shown++;
      do_actions_on_error(p, /*allow_db_attach*/True);
   } else {
      n_errs_suppressed++;
      p->supp->count++;
   }
}

/* Second top-level entry point to the error management subsystem, for
   errors that the tool wants to report immediately, eg. because they're
   guaranteed to only happen once.  This avoids all the recording and
   comparing stuff.  But they can be suppressed;  returns True if it is
   suppressed.  Bool `print_error' dictates whether to print the error. 
   Bool `count_error' dictates whether to count the error in n_errs_found.
*/
Bool VG_(unique_error) ( ThreadId tid, ErrorKind ekind, Addr a, Char* s,
                         void* extra, ExeContext* where, Bool print_error,
                         Bool allow_db_attach, Bool count_error )
{
   Error  err;

   /* Build ourselves the error */
   construct_error ( &err, tid, ekind, a, s, extra, where );

   /* Unless it's suppressed, we're going to show it.  Don't need to make
      a copy, because it's only temporary anyway.

      Then update the `extra' part with TL_(update_extra), because that can
      have an affect on whether it's suppressed.  Ignore the size return
      value of TL_(update_extra), because we're not copying `extra'. */
   (void)TL_(update_extra)(&err);

   if (NULL == is_suppressible_error(&err)) {
      if (count_error)
         n_errs_found++;

      if (print_error) {
         if (!is_first_shown_context)
            VG_(message)(Vg_UserMsg, "");
         pp_Error(&err, False);
         is_first_shown_context = False;
      }
      do_actions_on_error(&err, allow_db_attach);

      return False;

   } else {
      n_errs_suppressed++;
      return True;
   }
}


/*------------------------------------------------------------*/
/*--- Exported fns                                         ---*/
/*------------------------------------------------------------*/

/* These are called not from generated code but from the scheduler */

void VG_(record_pthread_error) ( ThreadId tid, Char* msg )
{
   if (! VG_(needs).core_errors) return;
   VG_(maybe_record_error)( tid, PThreadErr, /*addr*/0, msg, /*extra*/NULL );
}

void VG_(show_all_errors) ( void )
{
   Int    i, n_min;
   Int    n_err_contexts, n_supp_contexts;
   Error *p, *p_min;
   Supp  *su;
   Bool   any_supp;

   if (VG_(clo_verbosity) == 0)
      return;

   n_err_contexts = 0;
   for (p = vg_errors; p != NULL; p = p->next) {
      if (p->supp == NULL)
         n_err_contexts++;
   }

   n_supp_contexts = 0;
   for (su = vg_suppressions; su != NULL; su = su->next) {
      if (su->count > 0)
         n_supp_contexts++;
   }
   VG_(message)(Vg_UserMsg,
                "ERROR SUMMARY: "
                "%d errors from %d contexts (suppressed: %d from %d)",
                n_errs_found, n_err_contexts, 
                n_errs_suppressed, n_supp_contexts );

   if (VG_(clo_verbosity) <= 1)
      return;

   /* Print the contexts in order of increasing error count. */
   for (i = 0; i < n_err_contexts; i++) {
      n_min = (1 << 30) - 1;
      p_min = NULL;
      for (p = vg_errors; p != NULL; p = p->next) {
         if (p->supp != NULL) continue;
         if (p->count < n_min) {
            n_min = p->count;
            p_min = p;
         }
      }
      if (p_min == NULL) VG_(tool_panic)("show_all_errors()");

      VG_(message)(Vg_UserMsg, "");
      VG_(message)(Vg_UserMsg, "%d errors in context %d of %d:",
                   p_min->count,
                   i+1, n_err_contexts);
      pp_Error( p_min, False );

      if ((i+1 == VG_(clo_dump_error))) {
         VG_(translate) ( 0 /* dummy ThreadId; irrelevant due to debugging*/,
                          p_min->where->ips[0], /*debugging*/True, 
                          0xFE/*verbosity*/);
      }

      p_min->count = 1 << 30;
   } 

   if (n_supp_contexts > 0) 
      VG_(message)(Vg_DebugMsg, "");
   any_supp = False;
   for (su = vg_suppressions; su != NULL; su = su->next) {
      if (su->count > 0) {
         any_supp = True;
         VG_(message)(Vg_DebugMsg, "supp: %4d %s", su->count, su->sname);
      }
   }

   if (n_err_contexts > 0) {
      if (any_supp) 
         VG_(message)(Vg_UserMsg, "");
      VG_(message)(Vg_UserMsg,
                   "IN SUMMARY: "
                   "%d errors from %d contexts (suppressed: %d from %d)",
                   n_errs_found, n_err_contexts, n_errs_suppressed,
                   n_supp_contexts );
      VG_(message)(Vg_UserMsg, "");
   }
}

/*------------------------------------------------------------*/
/*--- Standard suppressions                                ---*/
/*------------------------------------------------------------*/

/* Get a non-blank, non-comment line of at most nBuf chars from fd.
   Skips leading spaces on the line. Return True if EOF was hit instead. 
*/

#define VG_ISSPACE(ch) (((ch)==' ') || ((ch)=='\n') || ((ch)=='\t'))

Bool VG_(get_line) ( Int fd, Char* buf, Int nBuf )
{
   Char ch;
   Int  n, i;
   while (True) {
      /* First, read until a non-blank char appears. */
      while (True) {
         n = VG_(read)(fd, &ch, 1);
         if (n == 1 && !VG_ISSPACE(ch)) break;
         if (n == 0) return True;
      }

      /* Now, read the line into buf. */
      i = 0;
      buf[i++] = ch; buf[i] = 0;
      while (True) {
         n = VG_(read)(fd, &ch, 1);
         if (n == 0) return False; /* the next call will return True */
         if (ch == '\n') break;
         if (i > 0 && i == nBuf-1) i--;
         buf[i++] = ch; buf[i] = 0;
      }
      while (i > 1 && VG_ISSPACE(buf[i-1])) { 
         i--; buf[i] = 0; 
      };

      /* VG_(printf)("The line is `%s'\n", buf); */
      /* Ok, we have a line.  If a non-comment line, return.
         If a comment line, start all over again. */
      if (buf[0] != '#') return False;
   }
}


/* *p_caller contains the raw name of a caller, supposedly either
       fun:some_function_name   or
       obj:some_object_name.
   Set *p_ty accordingly and advance *p_caller over the descriptor
   (fun: or obj:) part.
   Returns False if failed.
*/
static Bool setLocationTy ( Char** p_caller, SuppLocTy* p_ty )
{
   if (VG_(strncmp)(*p_caller, "fun:", 4) == 0) {
      (*p_caller) += 4;
      *p_ty = FunName;
      return True;
   }
   if (VG_(strncmp)(*p_caller, "obj:", 4) == 0) {
      (*p_caller) += 4;
      *p_ty = ObjName;
      return True;
   }
   VG_(printf)("location should start with fun: or obj:\n");
   return False;
}


/* Look for "tool" in a string like "tool1,tool2,tool3" */
static __inline__
Bool tool_name_present(Char *name, Char *names)
{
   Bool  found;
   Char *s = NULL;   /* Shut gcc up */
   Int   len = VG_(strlen)(name);

   found = (NULL != (s = VG_(strstr)(names, name)) &&
            (s        == names || *(s-1)   == ',') &&
            (*(s+len) == ','   || *(s+len) == '\0')
           );

   return found;
}

/* Read suppressions from the file specified in vg_clo_suppressions
   and place them in the suppressions list.  If there's any difficulty
   doing this, just give up -- there's no point in trying to recover.  
*/
static void load_one_suppressions_file ( Char* filename )
{
#  define N_BUF 200
   Int   fd, i;
   Bool  eof, too_many_contexts = False;
   Char  buf[N_BUF+1];
   Char* tool_names;
   Char* supp_name;

   fd = VG_(open)( filename, VKI_O_RDONLY, 0 );
   if (fd < 0) {
      VG_(message)(Vg_UserMsg, "FATAL: can't open suppressions file `%s'", 
                   filename );
      VG_(exit)(1);
   }

   while (True) {
      /* Assign and initialise the two suppression halves (core and tool) */
      Supp* supp;
      supp        = VG_(arena_malloc)(VG_AR_CORE, sizeof(Supp));
      supp->count = 0;
      for (i = 0; i < VG_N_SUPP_CALLERS; i++) supp->caller[i] = NULL;
      supp->string = supp->extra = NULL;

      eof = VG_(get_line) ( fd, buf, N_BUF );
      if (eof) break;

      if (!VG_STREQ(buf, "{")) goto syntax_error;
      
      eof = VG_(get_line) ( fd, buf, N_BUF );
      if (eof || VG_STREQ(buf, "}")) goto syntax_error;
      supp->sname = VG_(arena_strdup)(VG_AR_CORE, buf);

      eof = VG_(get_line) ( fd, buf, N_BUF );

      if (eof) goto syntax_error;

      /* Check it has the "tool1,tool2,...:supp" form (look for ':') */
      i = 0;
      while (True) {
         if (buf[i] == ':')  break;
         if (buf[i] == '\0') goto syntax_error;
         i++;
      }
      buf[i]    = '\0';    /* Replace ':', splitting into two strings */

      tool_names = & buf[0];
      supp_name  = & buf[i+1];

      /* Is it a core suppression? */
      if (VG_(needs).core_errors && tool_name_present("core", tool_names))
      {
         if (VG_STREQ(supp_name, "PThread"))
            supp->skind = PThreadSupp;
         else
            goto syntax_error;
      }

      /* Is it a tool suppression? */
      else if (VG_(needs).tool_errors && 
               tool_name_present(VG_(details).name, tool_names))
      {
         if (TL_(recognised_suppression)(supp_name, supp)) 
         {
            /* Do nothing, function fills in supp->skind */
         } else
            goto syntax_error;
      }

      else {
         /* Ignore rest of suppression */
         while (True) {
            eof = VG_(get_line) ( fd, buf, N_BUF );
            if (eof) goto syntax_error;
            if (VG_STREQ(buf, "}"))
               break;
         }
         continue;
      }

      if (VG_(needs).tool_errors && 
          !TL_(read_extra_suppression_info)(fd, buf, N_BUF, supp)) 
         goto syntax_error;

      /* "i > 0" ensures at least one caller read. */
      for (i = 0; i <= VG_N_SUPP_CALLERS; i++) {
         eof = VG_(get_line) ( fd, buf, N_BUF );
         if (eof) goto syntax_error;
         if (i > 0 && VG_STREQ(buf, "}")) 
            break;
         if (i == VG_N_SUPP_CALLERS)
            break;
         supp->caller[i] = VG_(arena_strdup)(VG_AR_CORE, buf);
         if (!setLocationTy(&(supp->caller[i]), &(supp->caller_ty[i])))
            goto syntax_error;
      }

      /* make sure to grab the '}' if the num callers is >=
         VG_N_SUPP_CALLERS */
      if (!VG_STREQ(buf, "}")) {
         // Don't just ignore extra lines -- abort.  (Someone complained
         // about silent ignoring of lines in bug #77922.)
         //do {
         //   eof = VG_(get_line) ( fd, buf, N_BUF );
         //} while (!eof && !VG_STREQ(buf, "}"));
         too_many_contexts = True;
         goto syntax_error;
      }

      supp->next = vg_suppressions;
      vg_suppressions = supp;
   }
   VG_(close)(fd);
   return;

  syntax_error:
   if (eof) {
      VG_(message)(Vg_UserMsg, 
                   "FATAL: in suppressions file `%s': unexpected EOF", 
                   filename );
   } else if (too_many_contexts) {
      VG_(message)(Vg_UserMsg, 
                   "FATAL: in suppressions file: `%s': at %s:", 
                   filename, buf );
      VG_(message)(Vg_UserMsg, 
                   "too many lines (limit of %d contexts in suppressions)",
                   VG_N_SUPP_CALLERS);
   } else {
      VG_(message)(Vg_UserMsg, 
                   "FATAL: in suppressions file: `%s': syntax error on: %s", 
                   filename, buf );
   }
   VG_(close)(fd);
   VG_(message)(Vg_UserMsg, "exiting now.");
   VG_(exit)(1);

#  undef N_BUF   
}


void VG_(load_suppressions) ( void )
{
   Int i;
   vg_suppressions = NULL;
   for (i = 0; i < VG_(clo_n_suppressions); i++) {
      if (VG_(clo_verbosity) > 1) {
         VG_(message)(Vg_UserMsg, "Reading suppressions file: %s", 
                                  VG_(clo_suppressions)[i] );
      }
      load_one_suppressions_file( VG_(clo_suppressions)[i] );
   }
}

/* Return the name of an erring fn in a way which is useful
   for comparing against the contents of a suppressions file. 
   Doesn't demangle the fn name, because we want to refer to 
   mangled names in the suppressions file.
*/
static void get_objname_fnname ( Addr a, Char* obj_buf, Int n_obj_buf,
                                         Char* fun_buf, Int n_fun_buf )
{     
   (void)VG_(get_objname)          ( a, obj_buf, n_obj_buf );
   (void)VG_(get_fnname_nodemangle)( a, fun_buf, n_fun_buf );
}     

static __inline__
Bool supp_matches_error(Supp* su, Error* err)
{
   switch (su->skind) {
      case PThreadSupp:
         return (err->ekind == PThreadErr);
      default:
         if (VG_(needs).tool_errors) {
            return TL_(error_matches_suppression)(err, su);
         } else {
            VG_(printf)(
               "\nUnhandled suppression type: %u.  VG_(needs).tool_errors\n"
               "probably needs to be set.\n",
               err->ekind);
            VG_(tool_panic)("unhandled suppression type");
         }
   }
}

static __inline__
Bool supp_matches_callers(Supp* su, Char caller_obj[][M_VG_ERRTXT], 
                                    Char caller_fun[][M_VG_ERRTXT])
{
   Int i;

   for (i = 0; i < VG_N_SUPP_CALLERS && su->caller[i] != NULL; i++) {
      switch (su->caller_ty[i]) {
         case ObjName: if (VG_(string_match)(su->caller[i],
                                             caller_obj[i])) break;
                       return False;
         case FunName: if (VG_(string_match)(su->caller[i], 
                                             caller_fun[i])) break;
                       return False;
         default: VG_(tool_panic)("supp_matches_callers");
      }
   }

   /* If we reach here, it's a match */
   return True;
}

/* Does an error context match a suppression?  ie is this a suppressible
   error?  If so, return a pointer to the Supp record, otherwise NULL.
   Tries to minimise the number of symbol searches since they are expensive.  
*/
static Supp* is_suppressible_error ( Error* err )
{
   Int i;

   static Char caller_obj[VG_N_SUPP_CALLERS][M_VG_ERRTXT];
   static Char caller_fun[VG_N_SUPP_CALLERS][M_VG_ERRTXT];

   Supp* su;

   /* get_objname_fnname() writes the function name and object name if
      it finds them in the debug info.  So the strings in the suppression
      file should match these.
   */

   /* Initialise these strs so they are always safe to compare, even
      if get_objname_fnname doesn't write anything to them. */
   for (i = 0; i < VG_N_SUPP_CALLERS; i++)
      caller_obj[i][0] = caller_fun[i][0] = 0;

   for (i = 0; i < VG_N_SUPP_CALLERS && i < VG_(clo_backtrace_size); i++) {
      get_objname_fnname ( err->where->ips[i], caller_obj[i], M_VG_ERRTXT,
                                               caller_fun[i], M_VG_ERRTXT );
   }

   /* See if the error context matches any suppression. */
   for (su = vg_suppressions; su != NULL; su = su->next) {
      if (supp_matches_error(su, err) &&
          supp_matches_callers(su, caller_obj, caller_fun)) {
         return su;
      }
   }
   return NULL;      /* no matches */
}

/*--------------------------------------------------------------------*/
/*--- end                                          vg_errcontext.c ---*/
/*--------------------------------------------------------------------*/