llext: add test for section and symbol alignment

Add a test case for the alignment support in loadable extensions. This
test case creates a set of constants with specific alignment requirements
and verifies that they are placed in memory as expected.

Fix the detached section test to use a more standard syntax for the
section attribute, avoiding issues with different toolchains.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

tests/subsys/llext/CMakeLists.txt

@@ -24,6 +24,7 @@ set(ext_names
 	threads_kernel_objects
 	export_dependent
 	export_dependency
+	align
 )
 
 if(CONFIG_ARM)

tests/subsys/llext/src/align_ext.c

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2025 Arduino SA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Define symbols with different alignment requirements and verify that LLEXT
+ * correctly handles them by testing the runtime address and the contents of
+ * each defined symbol.
+ */
+
+#include <stdint.h>
+#include <zephyr/kernel.h>
+#include <zephyr/llext/symbol.h>
+#include <zephyr/ztest_assert.h>
+
+/*
+ * Create constants requesting a specific alignment in memory and with a value
+ * that is related but not equal to their alignment requirement.
+ */
+#define ALIGNED_ENTRY(name, n) \
+	 const int name ## _ ## n __aligned(n) = n / 2 + 1
+
+ALIGNED_ENTRY(common, 8);
+ALIGNED_ENTRY(common, 16);
+ALIGNED_ENTRY(common, 32);
+ALIGNED_ENTRY(common, 64);
+ALIGNED_ENTRY(common, 128);
+ALIGNED_ENTRY(common, 256);
+ALIGNED_ENTRY(common, 512);
+
+/*
+ * Create similar constants in a set of independent sections to test merging.
+ */
+#define ALIGNED_SECT_ENTRY(name, n) \
+	Z_GENERIC_SECTION(name ## _sect_ ## n) ALIGNED_ENTRY(name, n)
+
+ALIGNED_SECT_ENTRY(independent, 8);
+ALIGNED_SECT_ENTRY(independent, 16);
+ALIGNED_SECT_ENTRY(independent, 32);
+ALIGNED_SECT_ENTRY(independent, 64);
+ALIGNED_SECT_ENTRY(independent, 128);
+ALIGNED_SECT_ENTRY(independent, 256);
+ALIGNED_SECT_ENTRY(independent, 512);
+
+/*
+ * Test that each symbol matches its expected value and alignment.
+ */
+#define ASSERT_ENTRY(name, n) \
+	zassert_equal(name ## _ ## n, n / 2 + 1); \
+	zassert_true(IS_ALIGNED(&name ## _ ## n, n))
+
+void test_entry(void)
+{
+	ASSERT_ENTRY(common, 8);
+	ASSERT_ENTRY(common, 16);
+	ASSERT_ENTRY(common, 32);
+	ASSERT_ENTRY(common, 64);
+	ASSERT_ENTRY(common, 128);
+	ASSERT_ENTRY(common, 256);
+	ASSERT_ENTRY(common, 512);
+
+	ASSERT_ENTRY(independent, 8);
+	ASSERT_ENTRY(independent, 16);
+	ASSERT_ENTRY(independent, 32);
+	ASSERT_ENTRY(independent, 64);
+	ASSERT_ENTRY(independent, 128);
+	ASSERT_ENTRY(independent, 256);
+	ASSERT_ENTRY(independent, 512);
+}
+EXPORT_SYMBOL(test_entry);

tests/subsys/llext/src/detached_fn_ext.c

@@ -9,7 +9,7 @@
 #include <zephyr/sys/printk.h>
 #include <zephyr/ztest_assert.h>
 
-__section(".detach") void detached_entry(void)
+Z_GENERIC_SECTION(.detach) void detached_entry(void)
 {
 	static int data_cnt = -3;
 	static unsigned int bss_cnt;

tests/subsys/llext/src/test_llext.c

@@ -316,6 +316,11 @@ LLEXT_LOAD_UNLOAD(threads_kernel_objects,
 	.test_setup = threads_objects_test_setup,
 )
 
+static LLEXT_CONST uint8_t align_ext[] ELF_ALIGN = {
+	#include "align.inc"
+};
+LLEXT_LOAD_UNLOAD(align)
+
 #ifndef CONFIG_LLEXT_TYPE_ELF_OBJECT
 static LLEXT_CONST uint8_t multi_file_ext[] ELF_ALIGN = {
 	#include "multi_file.inc"