stm32wl(mem): fix getFreeHeap() underreporting on dynamic sbrk heap

mallinfo().fordblks counts only free bytes within the committed arena.
On STM32WL (newlib sbrk heap) the arena grows lazily from _end toward SP,
so fordblks reads near-zero at early boot even when ~48 KB of addressable
space remains. This caused NodeDB::isFull() to fire prematurely and evict
nodes on a freshly booted device.

Fix getFreeHeap() to include uncommitted sbrk headroom (SP - sbrk(0)) so
the returned value reflects true available memory throughout the boot
lifecycle.

Introduce MESHTASTIC_DYNAMIC_SBRK_HEAP as an opt-in build flag (set in
stm32.ini) so the fix is gated to platforms with a dynamic sbrk heap
rather than a static heap. Future platforms with the same heap model can
opt in by adding this flag.

Signed-off-by: Andrew Yong <me@ndoo.sg>
Assisted-by: Claude Sonnet 4.6 <noreply@anthropic.com>

This commit is contained in:

Andrew Yong

2026-04-16 13:57:21 +01:00

committed by

Chloe Bethel

co-authored by

Chloe Bethel

parent 026213aab7

commit 0ee5777c15

2 changed files with 18 additions and 5 deletions

									
										variants/stm32/stm32.ini
									
		+1
		
												View File
												
				@@ -36,6 +36,7 @@ build_flags =

				  -DRADIOLIB_EXCLUDE_SX127X=1

				  -DRADIOLIB_EXCLUDE_LR11X0=1

				  -DRADIOLIB_EXCLUDE_LR2021=1

				  -DMESHTASTIC_DYNAMIC_SBRK_HEAP

				  -DHAL_DAC_MODULE_ONLY

				  -DHAL_RNG_MODULE_ENABLED

				  -Wl,--wrap=__assert_func