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Overview
Comment:Additional evidence marks on the malloc() implementation. Update the documentation to explain that mallocs are not necessarily 8-byte aligned if the SQLITE_4_BYTE_ALIGNED_MALLOC compile-time option is used.
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SHA1: 42b4bf9e72501cf228b4086437c7660443933f74
User & Date: drh 2010-09-11 16:15:56.000
Context
2010-09-11
16:25
Fix a couple of incorrect evidence marks on malloc(). (check-in: f9b5c5cb13 user: drh tags: trunk)
16:15
Additional evidence marks on the malloc() implementation. Update the documentation to explain that mallocs are not necessarily 8-byte aligned if the SQLITE_4_BYTE_ALIGNED_MALLOC compile-time option is used. (check-in: 42b4bf9e72 user: drh tags: trunk)
15:54
Add assert() statements to demonstrate that memory allocations are always aligned to an 8-byte boundary (unless SQLITE_4_BYTE_ALIGNED_MALLOC is defined). (check-in: 305cc4e6c1 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/malloc.c.
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/*
** Allocate memory.  This routine is like sqlite3_malloc() except that it
** assumes the memory subsystem has already been initialized.
*/
void *sqlite3Malloc(int n){
  void *p;

  if( n<=0 || n>=0x7fffff00 ){

    /* A memory allocation of a number of bytes which is near the maximum
    ** signed integer value might cause an integer overflow inside of the
    ** xMalloc().  Hence we limit the maximum size to 0x7fffff00, giving
    ** 255 bytes of overhead.  SQLite itself will never use anything near
    ** this amount.  The only way to reach the limit is with sqlite3_malloc() */
    p = 0;
  }else if( sqlite3GlobalConfig.bMemstat ){







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/*
** Allocate memory.  This routine is like sqlite3_malloc() except that it
** assumes the memory subsystem has already been initialized.
*/
void *sqlite3Malloc(int n){
  void *p;
  if( n<=0               /* IMP: R-65312-04917 */ 
   || n>=0x7fffff00
  ){
    /* A memory allocation of a number of bytes which is near the maximum
    ** signed integer value might cause an integer overflow inside of the
    ** xMalloc().  Hence we limit the maximum size to 0x7fffff00, giving
    ** 255 bytes of overhead.  SQLite itself will never use anything near
    ** this amount.  The only way to reach the limit is with sqlite3_malloc() */
    p = 0;
  }else if( sqlite3GlobalConfig.bMemstat ){
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  }
}

/*
** Free memory previously obtained from sqlite3Malloc().
*/
void sqlite3_free(void *p){
  if( p==0 ) return;
  assert( sqlite3MemdebugNoType(p, MEMTYPE_DB) );
  assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
  if( sqlite3GlobalConfig.bMemstat ){
    sqlite3_mutex_enter(mem0.mutex);
    sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, -sqlite3MallocSize(p));
    sqlite3StatusAdd(SQLITE_STATUS_MALLOC_COUNT, -1);
    sqlite3GlobalConfig.m.xFree(p);







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  }
}

/*
** Free memory previously obtained from sqlite3Malloc().
*/
void sqlite3_free(void *p){
  if( p==0 ) return;  /* IMP: R-49053-54554 */
  assert( sqlite3MemdebugNoType(p, MEMTYPE_DB) );
  assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
  if( sqlite3GlobalConfig.bMemstat ){
    sqlite3_mutex_enter(mem0.mutex);
    sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, -sqlite3MallocSize(p));
    sqlite3StatusAdd(SQLITE_STATUS_MALLOC_COUNT, -1);
    sqlite3GlobalConfig.m.xFree(p);
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/*
** Change the size of an existing memory allocation
*/
void *sqlite3Realloc(void *pOld, int nBytes){
  int nOld, nNew;
  void *pNew;
  if( pOld==0 ){
    return sqlite3Malloc(nBytes);
  }
  if( nBytes<=0 ){
    sqlite3_free(pOld);
    return 0;
  }
  if( nBytes>=0x7fffff00 ){
    /* The 0x7ffff00 limit term is explained in comments on sqlite3Malloc() */
    return 0;
  }
  nOld = sqlite3MallocSize(pOld);







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/*
** Change the size of an existing memory allocation
*/
void *sqlite3Realloc(void *pOld, int nBytes){
  int nOld, nNew;
  void *pNew;
  if( pOld==0 ){
    return sqlite3Malloc(nBytes); /* IMP: R-28354-25769 */
  }
  if( nBytes<=0 ){
    sqlite3_free(pOld); /* IMP: R-31593-10574 */
    return 0;
  }
  if( nBytes>=0x7fffff00 ){
    /* The 0x7ffff00 limit term is explained in comments on sqlite3Malloc() */
    return 0;
  }
  nOld = sqlite3MallocSize(pOld);
Changes to src/sqlite.h.in.
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** ^If M is the size of the prior allocation, then min(N,M) bytes
** of the prior allocation are copied into the beginning of buffer returned
** by sqlite3_realloc() and the prior allocation is freed.
** ^If sqlite3_realloc() returns NULL, then the prior allocation
** is not freed.
**
** ^The memory returned by sqlite3_malloc() and sqlite3_realloc()
** is always aligned to at least an 8 byte boundary.


**
** In SQLite version 3.5.0 and 3.5.1, it was possible to define
** the SQLITE_OMIT_MEMORY_ALLOCATION which would cause the built-in
** implementation of these routines to be omitted.  That capability
** is no longer provided.  Only built-in memory allocators can be used.
**
** The Windows OS interface layer calls







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** ^If M is the size of the prior allocation, then min(N,M) bytes
** of the prior allocation are copied into the beginning of buffer returned
** by sqlite3_realloc() and the prior allocation is freed.
** ^If sqlite3_realloc() returns NULL, then the prior allocation
** is not freed.
**
** ^The memory returned by sqlite3_malloc() and sqlite3_realloc()
** is always aligned to at least an 8 byte boundary, or to a
** 4 byte boundary if the [SQLITE_4_BYTE_ALIGNED_MALLOC] compile-time
** option is used.
**
** In SQLite version 3.5.0 and 3.5.1, it was possible to define
** the SQLITE_OMIT_MEMORY_ALLOCATION which would cause the built-in
** implementation of these routines to be omitted.  That capability
** is no longer provided.  Only built-in memory allocators can be used.
**
** The Windows OS interface layer calls