LCOV - code coverage report
Current view: top level - gltests - malloca.c (source / functions) Hit Total Coverage
Test: GNU SASL Lines: 23 24 95.8 %
Date: 2012-05-28 Functions: 2 2 100.0 %
Legend: Lines: hit not hit | Branches: + taken - not taken # not executed Branches: 7 12 58.3 %

           Branch data     Line data    Source code
       1                 :            : /* Safe automatic memory allocation.
       2                 :            :    Copyright (C) 2003, 2006-2007, 2009-2012 Free Software Foundation, Inc.
       3                 :            :    Written by Bruno Haible <bruno@clisp.org>, 2003.
       4                 :            : 
       5                 :            :    This program is free software; you can redistribute it and/or modify
       6                 :            :    it under the terms of the GNU General Public License as published by
       7                 :            :    the Free Software Foundation; either version 3, or (at your option)
       8                 :            :    any later version.
       9                 :            : 
      10                 :            :    This program is distributed in the hope that it will be useful,
      11                 :            :    but WITHOUT ANY WARRANTY; without even the implied warranty of
      12                 :            :    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      13                 :            :    GNU General Public License for more details.
      14                 :            : 
      15                 :            :    You should have received a copy of the GNU General Public License
      16                 :            :    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
      17                 :            : 
      18                 :            : #define _GL_USE_STDLIB_ALLOC 1
      19                 :            : #include <config.h>
      20                 :            : 
      21                 :            : /* Specification.  */
      22                 :            : #include "malloca.h"
      23                 :            : 
      24                 :            : #include <stdint.h>
      25                 :            : 
      26                 :            : #include "verify.h"
      27                 :            : 
      28                 :            : /* The speed critical point in this file is freea() applied to an alloca()
      29                 :            :    result: it must be fast, to match the speed of alloca().  The speed of
      30                 :            :    mmalloca() and freea() in the other case are not critical, because they
      31                 :            :    are only invoked for big memory sizes.  */
      32                 :            : 
      33                 :            : #if HAVE_ALLOCA
      34                 :            : 
      35                 :            : /* Store the mmalloca() results in a hash table.  This is needed to reliably
      36                 :            :    distinguish a mmalloca() result and an alloca() result.
      37                 :            : 
      38                 :            :    Although it is possible that the same pointer is returned by alloca() and
      39                 :            :    by mmalloca() at different times in the same application, it does not lead
      40                 :            :    to a bug in freea(), because:
      41                 :            :      - Before a pointer returned by alloca() can point into malloc()ed memory,
      42                 :            :        the function must return, and once this has happened the programmer must
      43                 :            :        not call freea() on it anyway.
      44                 :            :      - Before a pointer returned by mmalloca() can point into the stack, it
      45                 :            :        must be freed.  The only function that can free it is freea(), and
      46                 :            :        when freea() frees it, it also removes it from the hash table.  */
      47                 :            : 
      48                 :            : #define MAGIC_NUMBER 0x1415fb4a
      49                 :            : #define MAGIC_SIZE sizeof (int)
      50                 :            : /* This is how the header info would look like without any alignment
      51                 :            :    considerations.  */
      52                 :            : struct preliminary_header { void *next; char room[MAGIC_SIZE]; };
      53                 :            : /* But the header's size must be a multiple of sa_alignment_max.  */
      54                 :            : #define HEADER_SIZE \
      55                 :            :   (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max)
      56                 :            : struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; };
      57                 :            : verify (HEADER_SIZE == sizeof (struct header));
      58                 :            : /* We make the hash table quite big, so that during lookups the probability
      59                 :            :    of empty hash buckets is quite high.  There is no need to make the hash
      60                 :            :    table resizable, because when the hash table gets filled so much that the
      61                 :            :    lookup becomes slow, it means that the application has memory leaks.  */
      62                 :            : #define HASH_TABLE_SIZE 257
      63                 :            : static void * mmalloca_results[HASH_TABLE_SIZE];
      64                 :            : 
      65                 :            : #endif
      66                 :            : 
      67                 :            : void *
      68                 :     250000 : mmalloca (size_t n)
      69                 :            : {
      70                 :            : #if HAVE_ALLOCA
      71                 :            :   /* Allocate one more word, that serves as an indicator for malloc()ed
      72                 :            :      memory, so that freea() of an alloca() result is fast.  */
      73                 :     250000 :   size_t nplus = n + HEADER_SIZE;
      74                 :            : 
      75         [ +  - ]:     250000 :   if (nplus >= n)
      76                 :            :     {
      77                 :     250000 :       char *p = (char *) malloc (nplus);
      78                 :            : 
      79         [ +  - ]:     250000 :       if (p != NULL)
      80                 :            :         {
      81                 :            :           size_t slot;
      82                 :            : 
      83                 :     250000 :           p += HEADER_SIZE;
      84                 :            : 
      85                 :            :           /* Put a magic number into the indicator word.  */
      86                 :     250000 :           ((int *) p)[-1] = MAGIC_NUMBER;
      87                 :            : 
      88                 :            :           /* Enter p into the hash table.  */
      89                 :     250000 :           slot = (uintptr_t) p % HASH_TABLE_SIZE;
      90                 :     250000 :           ((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot];
      91                 :     250000 :           mmalloca_results[slot] = p;
      92                 :            : 
      93                 :     250000 :           return p;
      94                 :            :         }
      95                 :            :     }
      96                 :            :   /* Out of memory.  */
      97                 :     250000 :   return NULL;
      98                 :            : #else
      99                 :            : # if !MALLOC_0_IS_NONNULL
     100                 :            :   if (n == 0)
     101                 :            :     n = 1;
     102                 :            : # endif
     103                 :            :   return malloc (n);
     104                 :            : #endif
     105                 :            : }
     106                 :            : 
     107                 :            : #if HAVE_ALLOCA
     108                 :            : void
     109                 :     500000 : freea (void *p)
     110                 :            : {
     111                 :            :   /* mmalloca() may have returned NULL.  */
     112         [ +  - ]:     500000 :   if (p != NULL)
     113                 :            :     {
     114                 :            :       /* Attempt to quickly distinguish the mmalloca() result - which has
     115                 :            :          a magic indicator word - and the alloca() result - which has an
     116                 :            :          uninitialized indicator word.  It is for this test that sa_increment
     117                 :            :          additional bytes are allocated in the alloca() case.  */
     118         [ +  + ]:     500000 :       if (((int *) p)[-1] == MAGIC_NUMBER)
     119                 :            :         {
     120                 :            :           /* Looks like a mmalloca() result.  To see whether it really is one,
     121                 :            :              perform a lookup in the hash table.  */
     122                 :     250000 :           size_t slot = (uintptr_t) p % HASH_TABLE_SIZE;
     123                 :     250000 :           void **chain = &mmalloca_results[slot];
     124         [ +  - ]:     250000 :           for (; *chain != NULL;)
     125                 :            :             {
     126         [ +  - ]:     250000 :               if (*chain == p)
     127                 :            :                 {
     128                 :            :                   /* Found it.  Remove it from the hash table and free it.  */
     129                 :     250000 :                   char *p_begin = (char *) p - HEADER_SIZE;
     130                 :     250000 :                   *chain = ((struct header *) p_begin)->next;
     131                 :     250000 :                   free (p_begin);
     132                 :     500000 :                   return;
     133                 :            :                 }
     134                 :          0 :               chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next;
     135                 :            :             }
     136                 :            :         }
     137                 :            :       /* At this point, we know it was not a mmalloca() result.  */
     138                 :            :     }
     139                 :            : }
     140                 :            : #endif

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