Override exit and atexit functions from newlib.

This change simplify the exit and initialization process.
It also reduce the number of hidden memory allocation made by atexit.

hal/common/retarget.cpp

@@ -629,7 +629,7 @@ extern "C" void exit(int return_code) {
 } //namespace std
 #endif
 
-#if defined(TOOLCHAIN_ARM)
+#if defined(TOOLCHAIN_ARM) || defined(TOOLCHAIN_GCC)
 
 // This series of function disable the registration of global destructors
 // in a dynamic table which will be called when the application exit.
@@ -650,6 +650,39 @@ void __cxa_finalize(void *handle) {
 
 } // end of extern "C"
 
+#endif
+
+
+#if defined(TOOLCHAIN_GCC)
+
+/*
+ * Depending on how newlib is  configured, it is often not enough to define
+ * __aeabi_atexit, __cxa_atexit and __cxa_finalize in order to override the
+ * behavior regarding the registration of handlers with atexit.
+ *
+ * To overcome this limitation, exit and atexit are overriden here.
+ */
+extern "C"{
+
+/**
+ * @brief Retarget of exit for GCC.
+ * @details Unlike the standard version, this function doesn't call any function
+ * registered with atexit before calling _exit.
+ */
+void __wrap_exit(int return_code) {
+    _exit(return_code);
+}
+
+/**
+ * @brief Retarget atexit from GCC.
+ * @details This function will always fail and never register any handler to be
+ * called at exit.
+ */
+int __wrap_atexit(void (*func)()) {
+    return 1;
+}
+
+}
 
 #endif
 

tools/toolchains/gcc.py

@@ -40,7 +40,8 @@ class GCC(mbedToolchain):
         'c': ["-std=gnu99"],
         'cxx': ["-std=gnu++98", "-fno-rtti", "-Wvla"],
         'ld': ["-Wl,--gc-sections", "-Wl,--wrap,main",
-            "-Wl,--wrap,_malloc_r", "-Wl,--wrap,_free_r", "-Wl,--wrap,_realloc_r", "-Wl,--wrap,_calloc_r"],
+            "-Wl,--wrap,_malloc_r", "-Wl,--wrap,_free_r", "-Wl,--wrap,_realloc_r", "-Wl,--wrap,_calloc_r",
+            "-Wl,--wrap,exit", "-Wl,--wrap,atexit"],
     }
 
     def __init__(self, target, options=None, notify=None, macros=None, silent=False, tool_path="", extra_verbose=False):