This patch adds some runtime checks to prevent some potential
pointer overflow issues in the is_mem_free() function. The overflow
could happen in the case where the end addresses, computed as the
sum of a base address and a size, results in a value large enough
to wrap around. This, in turn, could lead to unpredictable behaviour.
If such an overflow is detected, the is_mem_free() function will now
declare the memory region as not free. The overflow is detected using
a new macro, called check_uptr_overflow().
This patch also modifies all other places in the 'bl_common.c' file
where an end address was computed as the sum of a base address and a
size and instead keeps the two values separate. This avoids the need
to handle pointer overflows everywhere. The code doesn't actually need
to compute any end address before the is_mem_free() function is called
other than to print information message to the serial output.
This patch also introduces 2 slight changes to the reserve_mem()
function:
- It fixes the end addresses passed to choose_mem_pos(). It was
incorrectly passing (base + size) instead of (base + size - 1).
- When the requested allocation size is 0, the function now exits
straight away and says so using a warning message.
Previously, it used to actually reserve some memory. A zero-byte
allocation was not considered as a special case so the function
was using the same top/bottom allocation mechanism as for any
other allocation. As a result, the smallest area of memory starting
from the requested base address within the free region was
reserved.
Change-Id: I0e695f961e24e56ffe000718014e0496dc6e1ec6
7b6d330c92