[libretiny] Keep a scan that finds no networks from resetting the LN882x (#20169)

esphome/components/libretiny/__init__.py

@@ -32,6 +32,7 @@ from esphome.storage_json import StorageJSON
 from . import gpio  # noqa: F401
 from .const import (
     COMPONENT_BK72XX,
+    COMPONENT_LN882X,
     CONF_GPIO_RECOVER,
     CONF_LOGLEVEL,
     CONF_SDK_SILENT,
@@ -490,6 +491,10 @@ async def component_to_code(config):
         # Not enabled on RTL87xx/LN882x — costs more heap than it saves there.
         cg.add_build_flag("-DconfigSUPPORT_STATIC_ALLOCATION=1")
 
+    # LN882x: a zero-size allocation must not trip the SDK's assert (see ln882x_zero_malloc.c).
+    if config[CONF_COMPONENT_ID] == COMPONENT_LN882X:
+        cg.add_build_flag("-Wl,--wrap=pvPortMalloc")
+
     # RTL8710B needs FreeRTOS 8.2.3+ for xTaskNotifyGive/ulTaskNotifyTake
     # required by AsyncTCP 3.4.3+ (https://github.com/esphome/esphome/issues/10220)
     # RTL8720C (ambz2) requires FreeRTOS 10.x so this only applies to RTL8710B

esphome/components/libretiny/ln882x_zero_malloc.c

@@ -0,0 +1,19 @@
+/*
+ * LN882x: heap_5 returns NULL for a zero-size request, and the SDK's
+ * malloc-failed hook ends in LN_ASSERT(0), which spins until the watchdog
+ * resets the chip. LibreTiny's scan handler asks for zero entries when a scan
+ * finds no networks. Linked with -Wl,--wrap=pvPortMalloc so every allocation
+ * comes through here; drop it once LibreTiny no longer allocates zero entries.
+ */
+
+#ifdef USE_LN882X
+
+#include <stddef.h>
+
+void *__real_pvPortMalloc(size_t size);  // NOLINT(readability-identifier-naming)
+
+void *__wrap_pvPortMalloc(size_t size) {  // NOLINT(readability-identifier-naming)
+  return __real_pvPortMalloc(size == 0 ? 1 : size);
+}
+
+#endif  // USE_LN882X