llext: add a test for the pre_located feature

This test checks that the pre_located feature works as expected. It
creates a new extension that is manually relocated to a specific address
via the add_llext_command() CMake function invoking a custom linker
command. The test then loads the extension setting the pre_located
option and checks that the symbol is resolved properly.

Signed-off-by: Luca Burelli <[email protected]>

Author: pillo79

tests/subsys/llext/simple/CMakeLists.txt

@@ -23,6 +23,10 @@ if(CONFIG_ARM)
   endif()
 endif()
 
+if (CONFIG_LLEXT_TYPE_ELF_RELOCATABLE AND CONFIG_XTENSA)
+    list(APPEND ext_names pre_located)
+endif()
+
 # generate extension targets foreach extension given by 'ext_names'
 foreach(ext_name ${ext_names})
   set(ext_src ${PROJECT_SOURCE_DIR}/src/${ext_name}_ext.c)
@@ -45,12 +49,15 @@ if(NOT CONFIG_LLEXT_TYPE_ELF_OBJECT)
   )
 endif()
 
-# Add a dummy custom processing command to test add_llext_command
-get_target_property(proc_in_file hello_world_ext lib_output)
-get_target_property(proc_out_file hello_world_ext pkg_input)
-add_llext_command(
-  TARGET hello_world_ext
-  POST_BUILD
-  COMMAND echo "dummy patching ${proc_in_file} to create ${proc_out_file}"
-  COMMAND ${CMAKE_COMMAND} -E copy ${proc_in_file} ${proc_out_file}
-)
+if (CONFIG_LLEXT_TYPE_ELF_RELOCATABLE AND CONFIG_XTENSA)
+  # Manually fix the pre_located extension's text address at a multiple of 4
+  get_target_property(pre_located_target pre_located_ext lib_target)
+  get_target_property(pre_located_file pre_located_ext pkg_input)
+  add_llext_command(
+    TARGET pre_located_ext
+    POST_BUILD
+    COMMAND ${CMAKE_C_COMPILER}
+    -Wl,-r -Wl,-Ttext=0xbada110c -nostdlib -nodefaultlibs -nostartfiles
+    $<TARGET_OBJECTS:${pre_located_target}> -o ${pre_located_file}
+  )
+endif()

tests/subsys/llext/simple/src/pre_located_ext.c

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2024 Arduino SA.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * This file contains a simple test extension that defines an entry point
+ * in the .text section. The entry point is never called, but the symbol
+ * address is fixed via a linker call and then checked by the test.
+ */
+
+#include <zephyr/llext/symbol.h>
+
+void test_entry(void)
+{
+	/* This function is never called */
+}
+LL_EXTENSION_SYMBOL(test_entry);

tests/subsys/llext/simple/src/test_llext_simple.c

@@ -237,6 +237,33 @@ static LLEXT_CONST uint8_t multi_file_ext[] __aligned(4) = {
 LLEXT_LOAD_UNLOAD(multi_file, true, NULL)
 #endif
 
+#if defined(CONFIG_LLEXT_TYPE_ELF_RELOCATABLE) && defined(CONFIG_XTENSA)
+static LLEXT_CONST uint8_t pre_located_ext[] __aligned(4) = {
+	#include "pre_located.inc"
+};
+
+ZTEST(llext, test_pre_located)
+{
+	struct llext_buf_loader buf_loader =
+		LLEXT_BUF_LOADER(pre_located_ext, ARRAY_SIZE(pre_located_ext));
+	struct llext_loader *loader = &buf_loader.loader;
+	struct llext_load_param ldr_parm = LLEXT_LOAD_PARAM_DEFAULT;
+	struct llext *ext = NULL;
+	const void *test_entry_fn;
+	int res;
+
+	/* load the extension trying to respect the addresses in the ELF */
+	ldr_parm.pre_located = true;
+	res = llext_load(loader, "pre_located", &ext, &ldr_parm);
+	zassert_ok(res, "load should succeed");
+
+	/* check the function address is the expected one */
+	test_entry_fn = llext_find_sym(&ext->exp_tab, "test_entry");
+	zassert_equal(test_entry_fn, (void *)0xbada110c, "test_entry should be at 0xbada110c");
+
+	llext_unload(&ext);
+}
+#endif
 
 /*
  * Ensure that EXPORT_SYMBOL does indeed provide a symbol and a valid address