LCOV - code coverage report
Current view: top level - lib/gltests - malloca.c (source / functions) Hit Total Coverage
Test: GNU Libidn Lines: 25 27 92.6 %
Date: 2013-07-10 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, 2009-2013 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; int magic; };
      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                 :            : union header {
      57                 :            :   void *next;
      58                 :            :   struct {
      59                 :            :     char room[HEADER_SIZE - MAGIC_SIZE];
      60                 :            :     int word;
      61                 :            :   } magic;
      62                 :            : };
      63                 :            : verify (HEADER_SIZE == sizeof (union header));
      64                 :            : /* We make the hash table quite big, so that during lookups the probability
      65                 :            :    of empty hash buckets is quite high.  There is no need to make the hash
      66                 :            :    table resizable, because when the hash table gets filled so much that the
      67                 :            :    lookup becomes slow, it means that the application has memory leaks.  */
      68                 :            : #define HASH_TABLE_SIZE 257
      69                 :            : static void * mmalloca_results[HASH_TABLE_SIZE];
      70                 :            : 
      71                 :            : #endif
      72                 :            : 
      73                 :            : void *
      74                 :     250000 : mmalloca (size_t n)
      75                 :            : {
      76                 :            : #if HAVE_ALLOCA
      77                 :            :   /* Allocate one more word, that serves as an indicator for malloc()ed
      78                 :            :      memory, so that freea() of an alloca() result is fast.  */
      79                 :     250000 :   size_t nplus = n + HEADER_SIZE;
      80                 :            : 
      81         [ +  - ]:     250000 :   if (nplus >= n)
      82                 :            :     {
      83                 :     250000 :       void *p = malloc (nplus);
      84                 :            : 
      85         [ +  - ]:     250000 :       if (p != NULL)
      86                 :            :         {
      87                 :            :           size_t slot;
      88                 :     250000 :           union header *h = p;
      89                 :            : 
      90                 :     250000 :           p = h + 1;
      91                 :            : 
      92                 :            :           /* Put a magic number into the indicator word.  */
      93                 :     250000 :           h->magic.word = MAGIC_NUMBER;
      94                 :            : 
      95                 :            :           /* Enter p into the hash table.  */
      96                 :     250000 :           slot = (uintptr_t) p % HASH_TABLE_SIZE;
      97                 :     250000 :           h->next = mmalloca_results[slot];
      98                 :     250000 :           mmalloca_results[slot] = p;
      99                 :            : 
     100                 :     250000 :           return p;
     101                 :            :         }
     102                 :            :     }
     103                 :            :   /* Out of memory.  */
     104                 :     250000 :   return NULL;
     105                 :            : #else
     106                 :            : # if !MALLOC_0_IS_NONNULL
     107                 :            :   if (n == 0)
     108                 :            :     n = 1;
     109                 :            : # endif
     110                 :            :   return malloc (n);
     111                 :            : #endif
     112                 :            : }
     113                 :            : 
     114                 :            : #if HAVE_ALLOCA
     115                 :            : void
     116                 :     500000 : freea (void *p)
     117                 :            : {
     118                 :            :   /* mmalloca() may have returned NULL.  */
     119         [ +  - ]:     500000 :   if (p != NULL)
     120                 :            :     {
     121                 :            :       /* Attempt to quickly distinguish the mmalloca() result - which has
     122                 :            :          a magic indicator word - and the alloca() result - which has an
     123                 :            :          uninitialized indicator word.  It is for this test that sa_increment
     124                 :            :          additional bytes are allocated in the alloca() case.  */
     125         [ +  + ]:     500000 :       if (((int *) p)[-1] == MAGIC_NUMBER)
     126                 :            :         {
     127                 :            :           /* Looks like a mmalloca() result.  To see whether it really is one,
     128                 :            :              perform a lookup in the hash table.  */
     129                 :     250000 :           size_t slot = (uintptr_t) p % HASH_TABLE_SIZE;
     130                 :     250000 :           void **chain = &mmalloca_results[slot];
     131         [ +  - ]:     250000 :           for (; *chain != NULL;)
     132                 :            :             {
     133                 :     250000 :               union header *h = p;
     134         [ +  - ]:     250000 :               if (*chain == p)
     135                 :            :                 {
     136                 :            :                   /* Found it.  Remove it from the hash table and free it.  */
     137                 :     250000 :                   union header *p_begin = h - 1;
     138                 :     250000 :                   *chain = p_begin->next;
     139                 :     250000 :                   free (p_begin);
     140                 :     500000 :                   return;
     141                 :            :                 }
     142                 :          0 :               h = *chain;
     143                 :          0 :               chain = &h[-1].next;
     144                 :            :             }
     145                 :            :         }
     146                 :            :       /* At this point, we know it was not a mmalloca() result.  */
     147                 :            :     }
     148                 :            : }
     149                 :            : #endif

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