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Comment:Avoid pointer aliasing in the allocSpace() routine in vdbeaux.c.
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SHA1: d6ae27512229d95502c584b17bb2cbdba401f80a
User & Date: drh 2009-12-08 15:35:23
Context
2009-12-08
19:05
Add tests to improve coverage of fts3. Associated bugfixes. check-in: f0eac417 user: dan tags: trunk
15:35
Avoid pointer aliasing in the allocSpace() routine in vdbeaux.c. check-in: d6ae2751 user: drh tags: trunk
15:16
Begin updating API documentation to use the new MD5-hash based automatic requirements numbering. Comment changes only. Many similar changes will follow. check-in: 973c5c86 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/vdbeaux.c.

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    z[j] = 0;
    sqlite3IoTrace("SQL %s\n", z);
  }
}
#endif /* !SQLITE_OMIT_TRACE && SQLITE_ENABLE_IOTRACE */

/*
** Allocate space from a fixed size buffer.  Make *pp point to the
** allocated space.  (Note:  pp is a char* rather than a void** to
** work around the pointer aliasing rules of C.)  *pp should initially
** be zero.  If *pp is not zero, that means that the space has already

** been allocated and this routine is a noop.



**
** nByte is the number of bytes of space needed.
**
** *ppFrom point to available space and pEnd points to the end of the
** available space.
**
** *pnByte is a counter of the number of bytes of space that have failed
** to allocate.  If there is insufficient space in *ppFrom to satisfy the
** request, then increment *pnByte by the amount of the request.
*/
static void allocSpace(
  char *pp,            /* IN/OUT: Set *pp to point to allocated buffer */
  int nByte,           /* Number of bytes to allocate */
  u8 **ppFrom,         /* IN/OUT: Allocate from *ppFrom */
  u8 *pEnd,            /* Pointer to 1 byte past the end of *ppFrom buffer */
  int *pnByte          /* If allocation cannot be made, increment *pnByte */
){
  assert( EIGHT_BYTE_ALIGNMENT(*ppFrom) );
  if( (*(void**)pp)==0 ){
    nByte = ROUND8(nByte);
    if( &(*ppFrom)[nByte] <= pEnd ){
      *(void**)pp = (void *)*ppFrom;
      *ppFrom += nByte;
    }else{
      *pnByte += nByte;
    }
  }

}

/*
** Prepare a virtual machine for execution.  This involves things such
** as allocating stack space and initializing the program counter.
** After the VDBE has be prepped, it can be executed by one or more
** calls to sqlite3VdbeExec().  
................................................................................
    }
    memset(zCsr, 0, zEnd-zCsr);
    zCsr += (zCsr - (u8*)0)&7;
    assert( EIGHT_BYTE_ALIGNMENT(zCsr) );

    do {
      nByte = 0;
      allocSpace((char*)&p->aMem, nMem*sizeof(Mem), &zCsr, zEnd, &nByte);
      allocSpace((char*)&p->aVar, nVar*sizeof(Mem), &zCsr, zEnd, &nByte);
      allocSpace((char*)&p->apArg, nArg*sizeof(Mem*), &zCsr, zEnd, &nByte);
      allocSpace((char*)&p->azVar, nVar*sizeof(char*), &zCsr, zEnd, &nByte);
      allocSpace((char*)&p->apCsr, 
                 nCursor*sizeof(VdbeCursor*), &zCsr, zEnd, &nByte
      );
      if( nByte ){
        p->pFree = sqlite3DbMallocZero(db, nByte);
      }
      zCsr = p->pFree;
      zEnd = &zCsr[nByte];
    }while( nByte && !db->mallocFailed );








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    z[j] = 0;
    sqlite3IoTrace("SQL %s\n", z);
  }
}
#endif /* !SQLITE_OMIT_TRACE && SQLITE_ENABLE_IOTRACE */

/*
** Allocate space from a fixed size buffer and return a pointer to
** that space.  If insufficient space is available, return NULL.
**
** The pBuf parameter is the initial value of a pointer which will
** receive the new memory.  pBuf is normally NULL.  If pBuf is not
** NULL, it means that memory space has already been allocated and that
** this routine should not allocate any new memory.  When pBuf is not
** NULL simply return pBuf.  Only allocate new memory space when pBuf
** is NULL.
**
** nByte is the number of bytes of space needed.
**
** *ppFrom point to available space and pEnd points to the end of the
** available space.
**
** *pnByte is a counter of the number of bytes of space that have failed
** to allocate.  If there is insufficient space in *ppFrom to satisfy the
** request, then increment *pnByte by the amount of the request.
*/
static void *allocSpace(
  void *pBuf,          /* Where return pointer will be stored */
  int nByte,           /* Number of bytes to allocate */
  u8 **ppFrom,         /* IN/OUT: Allocate from *ppFrom */
  u8 *pEnd,            /* Pointer to 1 byte past the end of *ppFrom buffer */
  int *pnByte          /* If allocation cannot be made, increment *pnByte */
){
  assert( EIGHT_BYTE_ALIGNMENT(*ppFrom) );
  if( pBuf ) return pBuf;
  nByte = ROUND8(nByte);
  if( &(*ppFrom)[nByte] <= pEnd ){
    pBuf = (void*)*ppFrom;
    *ppFrom += nByte;
  }else{
    *pnByte += nByte;
  }

  return pBuf;
}

/*
** Prepare a virtual machine for execution.  This involves things such
** as allocating stack space and initializing the program counter.
** After the VDBE has be prepped, it can be executed by one or more
** calls to sqlite3VdbeExec().  
................................................................................
    }
    memset(zCsr, 0, zEnd-zCsr);
    zCsr += (zCsr - (u8*)0)&7;
    assert( EIGHT_BYTE_ALIGNMENT(zCsr) );

    do {
      nByte = 0;
      p->aMem = allocSpace(p->aMem, nMem*sizeof(Mem), &zCsr, zEnd, &nByte);
      p->aVar = allocSpace(p->aVar, nVar*sizeof(Mem), &zCsr, zEnd, &nByte);
      p->apArg = allocSpace(p->apArg, nArg*sizeof(Mem*), &zCsr, zEnd, &nByte);
      p->azVar = allocSpace(p->azVar, nVar*sizeof(char*), &zCsr, zEnd, &nByte);
      p->apCsr = allocSpace(p->apCsr, nCursor*sizeof(VdbeCursor*),
                            &zCsr, zEnd, &nByte);

      if( nByte ){
        p->pFree = sqlite3DbMallocZero(db, nByte);
      }
      zCsr = p->pFree;
      zEnd = &zCsr[nByte];
    }while( nByte && !db->mallocFailed );