From 25e1b12ec0b356237f08e5613d944ecb5dc9a9ed Mon Sep 17 00:00:00 2001
From: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
Date: Mon, 31 May 2021 14:59:23 +0200
Subject: [PATCH] kernel: extract __weak main() into independent file

To support arm-ds / armlink it is required that the weak main is located
in an object externally to the object using the weak symbol.

If the weak symbol is inside the object referring to it, then the weak
symbol will be used and this will result in
```
Error: L6200E: Symbol __ARM_use_no_argv multiply defined
    (by init.o and main.o).
```
as both the weak and strong symbols are used.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
---
 kernel/CMakeLists.txt |  1 +
 kernel/init.c         |  6 ------
 kernel/main_weak.c    | 28 ++++++++++++++++++++++++++++
 3 files changed, 29 insertions(+), 6 deletions(-)
 create mode 100644 kernel/main_weak.c

diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index af311c38a42..4cecd2b3fd1 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -18,6 +18,7 @@ target_link_libraries(kernel INTERFACE ${libkernel})
 else()
 
 list(APPEND kernel_files
+  main_weak.c
   banner.c
   device.c
   errno.c
diff --git a/kernel/init.c b/kernel/init.c
index ddf8c3dc285..90abce0adae 100644
--- a/kernel/init.c
+++ b/kernel/init.c
@@ -235,12 +235,6 @@ static void bg_thread_main(void *unused1, void *unused2, void *unused3)
 
 /* LCOV_EXCL_START */
 
-void __weak main(void)
-{
-	/* NOP default main() if the application does not provide one. */
-	arch_nop();
-}
-
 /* LCOV_EXCL_STOP */
 
 #if defined(CONFIG_MULTITHREADING)
diff --git a/kernel/main_weak.c b/kernel/main_weak.c
new file mode 100644
index 00000000000..954d73e1de5
--- /dev/null
+++ b/kernel/main_weak.c
@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2010-2014 Wind River Systems, Inc.
+ * Copyright (c) 2021 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* Linkers may treat weak functions differently if they are located within
+ * the same object that calls the symbol or not.
+ *
+ * For example, when using armlink, then if the weak symbol is inside the object
+ * referring to it the weak symbol will be used. This will result in the symbol
+ * being multiply defined because both the weak and strong symbols are used.
+ *
+ * To GNU ld, it doesn't matter if the weak symbol is placed in the same object
+ * which uses the weak symbol. GNU ld will always link to the strong version.
+ *
+ * Having the weak main symbol in an independent file ensures that it will be
+ * correctly treated by multiple linkers.
+ */
+
+#include <kernel_internal.h>
+
+void __weak main(void)
+{
+	/* NOP default main() if the application does not provide one. */
+	arch_nop();
+}