tests/subsys/llext: Add syscall tests

Check if syscalls can be accessed from both kernel and userspace, and if
optimised away ones indeed point to NULL.

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>

tests/subsys/llext/simple/CMakeLists.txt

@@ -17,7 +17,7 @@ target_include_directories(app PRIVATE
 
 if(NOT LOADER_BUILD_ONLY)
 # generate extension targets foreach extension given by name
-foreach(ext_name hello_world logging relative_jump object)
+foreach(ext_name hello_world logging relative_jump object syscalls)
   set(ext_src ${PROJECT_SOURCE_DIR}/src/${ext_name}_ext.c)
   set(ext_bin ${ZEPHYR_BINARY_DIR}/${ext_name}.llext)
   set(ext_inc ${ZEPHYR_BINARY_DIR}/include/generated/${ext_name}.inc)

tests/subsys/llext/simple/prj.conf

@@ -4,3 +4,5 @@ CONFIG_LOG=y
 CONFIG_LLEXT=y
 CONFIG_LLEXT_HEAP_SIZE=16
 CONFIG_LLEXT_LOG_LEVEL_DBG=y
+
+CONFIG_APPLICATION_DEFINED_SYSCALL=y

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

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2024 Intel Corporation.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * This code demonstrates syscall support.
+ */
+
+#include <zephyr/llext/symbol.h>
+#include <zephyr/sys/printk.h>
+
+#include "syscalls_ext.h"
+
+void test_entry(void)
+{
+	int input = 41;
+
+	printk("Input: %d Expected output: %d Actual output: %d\n",
+	       input, input + 1, ext_syscall_ok(input));
+}
+LL_EXTENSION_SYMBOL(test_entry);

tests/subsys/llext/simple/src/syscalls_ext.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2024 Intel Corporation.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/sys/util.h>
+
+__syscall int ext_syscall_ok(int a);
+
+/*
+ * This is a syscall that is intentionally not implemented. The build
+ * syscall machinery will still pick it up and generate a stub for it,
+ * that should be optmised away. For extensions, the symbol will end up
+ * pointing to NULL. This is tested in the test_ext_syscall_fail test.
+ */
+__syscall void ext_syscall_fail(void);
+
+#include <syscalls/syscalls_ext.h>

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

@@ -11,6 +11,8 @@
 #include <zephyr/logging/log.h>
 #include <zephyr/sys/libc-hooks.h>
 
+#include "syscalls_ext.h"
+
 LOG_MODULE_REGISTER(test_llext_simple);
 
 
@@ -43,6 +45,19 @@ void llext_entry(void *arg0, void *arg1, void *arg2)
 }
 #endif /* CONFIG_USERSPACE */
 
+int z_impl_ext_syscall_ok(int a)
+{
+	return a + 1;
+}
+
+#ifdef CONFIG_USERSPACE
+static inline int z_vrfy_ext_syscall_ok(int a)
+{
+	return z_impl_ext_syscall_ok(a);
+}
+#include <syscalls/ext_syscall_ok_mrsh.c>
+#endif /* CONFIG_USERSPACE */
+
 void load_call_unload(struct llext_test *test_case)
 {
 	struct llext_buf_loader buf_loader =
@@ -158,6 +173,11 @@ static LLEXT_CONST uint8_t object_ext[] __aligned(4) = {
 	#include "object.inc"
 };
 LLEXT_LOAD_UNLOAD(object, true)
+
+static LLEXT_CONST uint8_t syscalls_ext[] __aligned(4) = {
+	#include "syscalls.inc"
+};
+LLEXT_LOAD_UNLOAD(syscalls, true)
 #endif /* ! LOADER_BUILD_ONLY */
 
 /*
@@ -171,5 +191,17 @@ ZTEST(llext, test_printk_exported)
 	zassert_equal(printk_fn, printk, "printk should be an exported symbol");
 }
 
+/*
+ * Ensure ext_syscall_fail is exported - as it is picked up by the syscall
+ * build machinery - but points to NULL as it is not implemented.
+ */
+ZTEST(llext, test_ext_syscall_fail)
+{
+	const void * const esf_fn = llext_find_sym(NULL,
+						   "z_impl_ext_syscall_fail");
+
+	zassert_is_null(*(uintptr_t **)esf_fn, NULL,
+			"ext_syscall_fail should be NULL");
+}
 
 ZTEST_SUITE(llext, NULL, NULL, NULL, NULL, NULL);