The commit 84d0689 "Nano-malloc: Fix for unwanted external heap
fragmentation" from newlib 4.1.0 introduced several optimizations,
one of which is as follows:
When the last chunk in the free list is smaller than requested,
nano_malloc() calls sbrk(0) to see if the heap's current head is
adjacent to this chunk, and if so it asks sbrk() to allocate the
difference in bytes only and expands the current chunk.
This doesn't work if the heap consists of non-contiguous regions.
sbrk(0) returns the the current region's head if the region has any
remaining capacity. But if this capacity is not enough for the second
(non-trivial) call to sbrk() described above, allocation will happen
from the next region if available. Expanding the current chunk won't
work and will result in a segmentation fault.
So this optimization needs to be reverted in order to bring back
compatibility with non-contiguous heaps. Before the next version
of newlib becomes available and gets updated in the GCC Arm Embedded
Toolchain, we work around this issue by including the fix in Mbed OS.
The linker prioritizes malloc() from the project to the one from the
toolchain.
mbed-os consists of mbed-core and mbed-rtos
mbed-baremetal consists of mbed-core
The main change is for mbed-core. Changing from object library to be interface. This way it allows us to do the above to have 2 main targets for users to use.
This should be backward compatible change as mbed-os target we used contains the same files/options as previously set.
Aside from the core mbed-os CMake target, a number of targets have been created so they can optionally be included by application executables that require them using `target_link_libraries()`.
Co-authored-by: Martin Kojtal <martin.kojtal@arm.com>
Co-authored-by: Rajkumar Kanagaraj <rajkumar.kanagaraj@arm.com>
Lingkai Dong
Martin Kojtal
Rajkumar Kanagaraj
Hugues Kamba
Hugues Kamba