loader: Redirect malloc to kernel heap.

Replace the libc's malloc, free etc.. with wrappers that redirect
memory allocation Zephyr's kernel heap functions (k_malloc/k_free).

Signed-off-by: iabdalkader <[email protected]>

Author: iabdalkader

extra/build.sh

@@ -104,11 +104,6 @@ extra/gen_provides.py "${BUILD_DIR}/zephyr/zephyr.elf" -LF \
 	"+kheap_llext_heap" \
 	"+kheap__system_heap" \
 	"*sketch_base_addr=_sketch_start" \
-	"*sketch_max_size=_sketch_max_size" \
-	"malloc=__wrap_malloc" \
-	"free=__wrap_free" \
-	"realloc=__wrap_realloc" \
-	"calloc=__wrap_calloc" \
-	"random=__wrap_random" > ${VARIANT_DIR}/syms-static.ld
+	"*sketch_max_size=_sketch_max_size" > ${VARIANT_DIR}/syms-static.ld
 
 cmake -P extra/gen_arduino_files.cmake $variant

loader/CMakeLists.txt

@@ -25,4 +25,12 @@ FILE(GLOB app_sources *.c)
 target_sources(app PRIVATE ${app_sources})
 target_compile_definitions(app PUBLIC _XOPEN_SOURCE=700)
 
+# Wrap malloc, free, calloc and realloc
+zephyr_ld_options(
+	-Wl,--wrap=malloc
+	-Wl,--wrap=free
+	-Wl,--wrap=calloc
+	-Wl,--wrap=realloc
+)
+
 target_link_libraries(app PUBLIC blobs)

loader/llext_exports.c

@@ -276,10 +276,7 @@ FORCE_EXPORT_SYM(__aeabi_idivmod);
 FORCE_EXPORT_SYM(__aeabi_ldivmod);
 FORCE_EXPORT_SYM(__aeabi_ul2f);
 FORCE_EXPORT_SYM(__aeabi_dcmpge);
-
-#if defined (CONFIG_CPP)
 FORCE_EXPORT_SYM(__cxa_pure_virtual);
-#endif
 
 #if defined(CONFIG_BOARD_ARDUINO_UNO_Q)
 FORCE_EXPORT_SYM(matrixBegin);

loader/malloc_wrapper.c

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2025 Arduino SA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Wrapper to redirect malloc/free to k_malloc/k_free using ld --wrap
+ */
+
+#include <zephyr/kernel.h>
+
+void *__wrap_malloc(size_t size) {
+	return k_malloc(size);
+}
+
+void __wrap_free(void *ptr) {
+	k_free(ptr);
+}
+
+void *__wrap_calloc(size_t nmemb, size_t size) {
+	return k_calloc(nmemb, size);
+}
+
+void *__wrap_realloc(void *ptr, size_t size) {
+	return k_realloc(ptr, size);
+}

platform.txt

@@ -63,7 +63,7 @@ build.combine_command={build.link_command} {build.link_args.build-{build.link_mo
 
 # link_args.* are included by any link_command depending on the link_mode
 build.link_args.dynamic=-e main
-build.link_args.static=-lc -lm -lgcc -Wl,--wrap=random -Wl,--wrap=calloc -Wl,--wrap=free -Wl,--wrap=malloc -Wl,--wrap=realloc
+build.link_args.static=-lc -lm -lgcc
 
 # link_args.check-* are used to check the build. Only LLEXT needs these to emulate a static build (no -r!).
 build.link_args.check-dynamic="-T{build.variant.path}/syms-dynamic.ld" "-T{build.ldscript.path}/memory-check.ld" "-T{build.ldscript.path}/build-static.ld"