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In the debugging memory allocator, initialize new memory allocations to

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pseudo-randomness in an effort to find problems with memcmp() of structures
that have uninitialized pad bytes.

FossilOrigin-Name: 6462817b2f817a6105449b0ea3e1e336e42571d1
This commit is contained in:
drh
2010-01-05 03:30:15 +00:00
parent 9061ad10bc
commit 10f864e8ef
3 changed files with 40 additions and 14 deletions
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34
src/mem2.c
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@@ -210,6 +210,31 @@ static int sqlite3MemRoundup(int n){
return ROUND8(n);
}
/*
** Fill a buffer with pseudo-random bytes. This is used to preset
** the content of a new memory allocation to unpredictable values and
** to clear the content of a freed allocation to unpredictable values.
*/
static void randomFill(char *pBuf, int nByte){
unsigned int x, y, r;
x = SQLITE_PTR_TO_INT(pBuf);
y = nByte | 1;
while( nByte >= 4 ){
x = (x>>1) ^ (-(x&1) & 0xd0000001);
y = y*1103515245 + 12345;
r = x ^ y;
*(int*)pBuf = r;
pBuf += 4;
nByte -= 4;
}
while( nByte-- > 0 ){
x = (x>>1) ^ (-(x&1) & 0xd0000001);
y = y*1103515245 + 12345;
r = x ^ y;
*(pBuf++) = r & 0xff;
}
}
/*
** Allocate nByte bytes of memory.
*/
@@ -260,7 +285,8 @@ static void *sqlite3MemMalloc(int nByte){
adjustStats(nByte, +1);
pInt = (int*)&pHdr[1];
pInt[nReserve/sizeof(int)] = REARGUARD;
memset(pInt, 0x65, nReserve);
randomFill((char*)pInt, nByte);
memset(((char*)pInt)+nByte, 0x65, nReserve-nByte);
p = (void*)pInt;
}
sqlite3_mutex_leave(mem.mutex);
@@ -296,8 +322,8 @@ static void sqlite3MemFree(void *pPrior){
z = (char*)pBt;
z -= pHdr->nTitle;
adjustStats(pHdr->iSize, -1);
memset(z, 0x2b, sizeof(void*)*pHdr->nBacktraceSlots + sizeof(*pHdr) +
pHdr->iSize + sizeof(int) + pHdr->nTitle);
randomFill(z, sizeof(void*)*pHdr->nBacktraceSlots + sizeof(*pHdr) +
pHdr->iSize + sizeof(int) + pHdr->nTitle);
free(z);
sqlite3_mutex_leave(mem.mutex);
}
@@ -320,7 +346,7 @@ static void *sqlite3MemRealloc(void *pPrior, int nByte){
if( pNew ){
memcpy(pNew, pPrior, nByte<pOldHdr->iSize ? nByte : pOldHdr->iSize);
if( nByte>pOldHdr->iSize ){
memset(&((char*)pNew)[pOldHdr->iSize], 0x2b, nByte - pOldHdr->iSize);
randomFill(&((char*)pNew)[pOldHdr->iSize], nByte - pOldHdr->iSize);
}
sqlite3MemFree(pPrior);
}