inline size_t
nsRuleData::GetPoisonOffset()
{
// Fill in mValueOffsets such that mValueStorage + mValueOffsets[i]
// will yield the frame poison value for all uninitialized value
// offsets.
MOZ_STATIC_ASSERT(sizeof(PRUword) == sizeof(size_t),
"expect PRUword and size_t to be the same size");
MOZ_STATIC_ASSERT(PRUword(-1) > PRUword(0),
"expect PRUword to be unsigned");
MOZ_STATIC_ASSERT(size_t(-1) > size_t(0),
"expect size_t to be unsigned");
PRUword framePoisonValue = nsPresArena::GetPoisonValue();
return size_t(framePoisonValue - PRUword(mValueStorage)) /
sizeof(nsCSSValue);
}
static PRUword
ReservePoisonArea(PRUword rgnsize)
{
if (sizeof(PRUword) == 8) {
// Use the hardware-inaccessible region.
// We have to avoid 64-bit constants and shifts by 32 bits, since this
// code is compiled in 32-bit mode, although it is never executed there.
return
(((PRUword(0x7FFFFFFFu) << 31) << 1 | PRUword(0xF0DEAFFFu))
& ~(rgnsize-1));
} else {
// First see if we can allocate the preferred poison address from the OS.
PRUword candidate = (0xF0DEAFFF & ~(rgnsize-1));
void *result = ReserveRegion(candidate, rgnsize);
if (result == (void *)candidate) {
// success - inaccessible page allocated
return candidate;
}
// That didn't work, so see if the preferred address is within a range
// of permanently inacessible memory.
if (ProbeRegion(candidate, rgnsize)) {
// success - selected page cannot be usable memory
if (result != RESERVE_FAILED)
ReleaseRegion(result, rgnsize);
return candidate;
}
// The preferred address is already in use. Did the OS give us a
// consolation prize?
if (result != RESERVE_FAILED) {
return PRUword(result);
}
// It didn't, so try to allocate again, without any constraint on
// the address.
result = ReserveRegion(0, rgnsize);
if (result != RESERVE_FAILED) {
return PRUword(result);
}
NS_RUNTIMEABORT("no usable poison region identified");
return 0;
}
}
