loader: Redirect sketch malloc to kernel heap.

Replace the libc malloc/free with Zephyr's kernel heap functions
(k_malloc/k_free) for sketch memory allocation.

This is achieved by using EXPORT_SYMBOL_NAMED to alias k_malloc as malloc,
k_free as free, k_calloc as calloc, and k_realloc as realloc in the llext
symbol table. When sketches call malloc(), the llext loader resolves these
to the kernel heap functions.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>

Author: iabdalkader

extra/build.sh

@@ -100,15 +100,10 @@ cp ${BUILD_DIR}/zephyr/.config firmwares/zephyr-$variant.config
 # Generate the provides.ld file for linked builds
 echo "Generating exported symbol scripts"
 extra/gen_provides.py "${BUILD_DIR}/zephyr/zephyr.elf" -L > ${VARIANT_DIR}/syms-dynamic.ld
-extra/gen_provides.py "${BUILD_DIR}/zephyr/zephyr.elf" -LF \
+extra/gen_provides.py "${BUILD_DIR}/zephyr/zephyr.elf" -L \
 	"+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/llext_exports.c

@@ -24,12 +24,10 @@ EXPORT_SYMBOL(strchr);
 EXPORT_SYMBOL(strcat);
 EXPORT_SYMBOL(memmove);
 
-EXPORT_SYMBOL(k_malloc);
-EXPORT_SYMBOL(k_free);
-EXPORT_SYMBOL(malloc);
-EXPORT_SYMBOL(realloc);
-EXPORT_SYMBOL(calloc);
-EXPORT_SYMBOL(free);
+EXPORT_SYMBOL_NAMED(k_malloc, malloc);
+EXPORT_SYMBOL_NAMED(k_free, free);
+EXPORT_SYMBOL_NAMED(k_calloc, calloc);
+EXPORT_SYMBOL_NAMED(k_realloc, realloc);
 EXPORT_SYMBOL(rand);
 EXPORT_SYMBOL(srand);
 

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"