libc/picolibc: Rework malloc arena setup
Picolibc inherited its malloc arena configuration from newlib instead of
from minimal libc. This ended up making it a bit too fragile to run the
full set of zephyr tests. In particular:
* Z_MALLOC_PARTITION_EXISTS would get set when not used
* Setting an arena size depended on a bunch of other values, including
whether the system had an MMU or MPU, and whether the MPU required
power-of-two alignment or not.
This patch cleans things up so that there is a single heap size specifier,
PICOLIBC_HEAP_SIZE.
* If PICOLIBC_HEAP_SIZE is positive, this sets the size of the heap. On
MMU systems, picolibc will only use the remaining memory if that's
smaller.
* If PICOLIBC_HEAP_SIZE is zero, then there is no heap available and
malloc will always fail. This also disables Z_MALLOC_PARTITION_EXISTS.
* If PICOLIBC_HEAP_SIZE is negative, then picolibc uses all remaining
memory for the malloc heap.
The defaults are designed to allow tests to work without requiring
additional settings.
* For MMU enabled systems, the default value is 1048576. It would be nice
to have this use 'all available memory', but that's difficult to manage
as the API which returns free memory (k_mem_free_get) doesn't take into
account the amount of free virtual address space.
* For MPU enabled systems which require power-of-two aligned MPU regions,
the default value is 64kB.
* For other systems, the default value is -1, indicating that all
available memory be used for the malloc arena.
Signed-off-by: Keith Packard <keithp@keithp.com>
3 files changed
