Adding debugger awarness with Keil MDK

Main thread in Mbed OS is statically allocated and was not available in call
stack of Keil MDK. The RTX5 kernel requires statically allocated thread
information objects that are placed into a specific section to enable RTOS
thread awareness in Keil MDK. This fix is to keep main thread in specific
section of memory.

Author: Deepika

rtos/TARGET_CORTEX/mbed_rtos_rtx.c

@@ -51,7 +51,7 @@ osThreadAttr_t _main_thread_attr;
 #define MBED_CONF_APP_MAIN_STACK_SIZE MBED_CONF_RTOS_MAIN_THREAD_STACK_SIZE
 #endif
 MBED_ALIGN(8) char _main_stack[MBED_CONF_APP_MAIN_STACK_SIZE];
-mbed_rtos_storage_thread_t _main_obj;
+mbed_rtos_storage_thread_t _main_obj __attribute__((section(".bss.os.thread.cb")));
 
 osMutexId_t               singleton_mutex_id;
 mbed_rtos_storage_mutex_t singleton_mutex_obj;

tools/profiles/debug.json

@@ -24,7 +24,7 @@
         "asm": [],
         "c": ["-D__ASSERT_MSG", "-std=gnu99"],
         "cxx": ["-fno-rtti", "-std=gnu++98"],
-        "ld": ["--verbose", "--remove", "--show_full_path", "--legacyalign"]
+        "ld": ["--verbose", "--remove", "--show_full_path", "--legacyalign", "--keep=os_cb_sections"]
     },
     "ARM": {
         "common": ["-c", "--gnu", "-Otime", "--split_sections",
@@ -34,7 +34,7 @@
         "asm": [],
         "c": ["--md", "--no_depend_system_headers", "--c99", "-D__ASSERT_MSG"],
         "cxx": ["--cpp", "--no_rtti", "--no_vla"],
-        "ld": ["--show_full_path"]
+        "ld": ["--show_full_path", "--keep=os_cb_sections"]
     },
     "uARM": {
         "common": ["-c", "--gnu", "-Otime", "--split_sections",

tools/profiles/develop.json

@@ -23,7 +23,7 @@
         "asm": [],
         "c": ["-D__ASSERT_MSG", "-std=gnu99"],
         "cxx": ["-fno-rtti", "-std=gnu++98"],
-        "ld": ["--show_full_path", "--legacyalign"]
+        "ld": ["--show_full_path", "--legacyalign", "--keep=os_cb_sections"]
     },
     "ARM": {
         "common": ["-c", "--gnu", "-Otime", "--split_sections",
@@ -32,7 +32,7 @@
         "asm": [],
         "c": ["--md", "--no_depend_system_headers", "--c99", "-D__ASSERT_MSG"],
         "cxx": ["--cpp", "--no_rtti", "--no_vla"],
-        "ld": ["--show_full_path"]
+        "ld": ["--show_full_path", "--keep=os_cb_sections"]
     },
     "uARM": {
         "common": ["-c", "--gnu", "-Otime", "--split_sections",

tools/profiles/release.json

@@ -23,7 +23,7 @@
         "asm": [],
         "c": ["-D__ASSERT_MSG", "-std=gnu99"],
         "cxx": ["-fno-rtti", "-std=gnu++98"],
-        "ld": ["--show_full_path", "--legacyalign"]
+        "ld": ["--show_full_path", "--legacyalign", "--keep=os_cb_sections"]
     },
     "ARM": {
         "common": ["-c", "--gnu", "-Ospace", "--split_sections",
@@ -32,7 +32,7 @@
         "asm": [],
         "c": ["--md", "--no_depend_system_headers", "--c99", "-D__ASSERT_MSG"],
         "cxx": ["--cpp", "--no_rtti", "--no_vla"],
-        "ld": ["--show_full_path"]
+        "ld": ["--show_full_path",  "--keep=os_cb_sections"]
     },
     "uARM": {
         "common": ["-c", "--gnu", "-Ospace", "--split_sections",