libc: fix executable destruction support.

This change allows an executable to call its destructor functions
(declared with __attribute__((destructor))) to be properly called
when it normally exits.

Note that this is different from calling the destructors of a shared
library when it is unloaded with dlclose() or through program exit,
which are already supported.

Bug: 3106500
Change-Id: I1412ef5407f13b613fc6cb6103e0a691dbee4b1a

4 files changed, 61 insertions, 5 deletions

diff --git a/libc/bionic/libc_init_common.c b/libc/bionic/libc_init_common.c
index d78d673..f7579bd 100644
--- a/libc/bionic/libc_init_common.c
+++ b/libc/bionic/libc_init_common.c
@@ -84,3 +84,39 @@ void __libc_init_common(uintptr_t *elfdata)
     /* setup system properties - requires environment */
     __system_properties_init();
 }
+
+/* This function will be called during normal program termination
+ * to run the destructors that are listed in the .fini_array section
+ * of the executable, if any.
+ *
+ * 'fini_array' points to a list of function addresses. The first
+ * entry in the list has value -1, the last one has value 0.
+ */
+void __libc_fini(void* array)
+{
+    int count;
+    void** fini_array = array;
+    const size_t  minus1 = ~(size_t)0; /* ensure proper sign extension */
+
+    /* Sanity check - first entry must be -1 */
+    if (array == NULL || (size_t)fini_array[0] != minus1) {
+        return;
+    }
+
+    /* skip over it */
+    fini_array += 1;
+
+    /* Count the number of destructors. */
+    for (count = 0; fini_array[count] != NULL; count++);
+
+    /* Now call each destructor in reverse order. */
+    while (count > 0) {
+        void (*func)() = (void (*)) fini_array[--count];
+
+        /* Sanity check, any -1 in the list is ignored */
+        if ((size_t)func == minus1)
+            continue;
+
+        func();
+    }
+}
diff --git a/libc/bionic/libc_init_common.h b/libc/bionic/libc_init_common.h
index 8663c61..6016d4d 100644
--- a/libc/bionic/libc_init_common.h
+++ b/libc/bionic/libc_init_common.h
@@ -39,5 +39,6 @@ typedef struct
 } structors_array_t;
 
 extern void __libc_init_common(uintptr_t *elfdata);
+extern void __libc_fini(void* finit_array);
 
 #endif
diff --git a/libc/bionic/libc_init_dynamic.c b/libc/bionic/libc_init_dynamic.c
index 682ebcf..f64b6f2 100644
--- a/libc/bionic/libc_init_dynamic.c
+++ b/libc/bionic/libc_init_dynamic.c
@@ -57,9 +57,9 @@
  * This ensures that the function is called by the dynamic linker
  * as soon as the shared library is loaded.
  */
-void __attribute__((constructor)) __libc_prenit(void);
+void __attribute__((constructor)) __libc_preinit(void);
 
-void __libc_prenit(void)
+void __libc_preinit(void)
 {
     /* Read the ELF data pointer form a special slot of the
      * TLS area, then call __libc_init_common with it.
@@ -83,14 +83,19 @@ void __libc_prenit(void)
     malloc_debug_init();
 }
 
+/* This function is called from the executable's _start entry point
+ * (see arch-$ARCH/bionic/crtbegin_dynamic.S), which is itself
+ * called by the dynamic linker after it has loaded all shared
+ * libraries the executable depends on.
+ *
+ * Note that the dynamic linker has also run all constructors in the
+ * executable at this point.
+ */
 __noreturn void __libc_init(uintptr_t *elfdata,
                        void (*onexit)(void),
                        int (*slingshot)(int, char**, char**),
                        structors_array_t const * const structors)
 {
-    /* When we reach this point, all initializers have been already
-     * run by the dynamic linker, so ignore 'structors'.
-     */
     int     argc = (int)*elfdata;
     char**  argv = (char**)(elfdata + 1);
     char**  envp = argv + argc + 1;
@@ -99,5 +104,12 @@ __noreturn void __libc_init(uintptr_t *elfdata,
      * do never use it.  Therefore, we ignore it.
      */
 
+    /* The executable may have its own destructors listed in its .fini_array
+     * so we need to ensure that these are called when the program exits
+     * normally.
+     */
+    if (structors->fini_array)
+        __cxa_atexit(__libc_fini,structors->fini_array,NULL);
+
     exit(slingshot(argc, argv, envp));
 }
diff --git a/libc/bionic/libc_init_static.c b/libc/bionic/libc_init_static.c
index d097b6b..3634c7b 100644
--- a/libc/bionic/libc_init_static.c
+++ b/libc/bionic/libc_init_static.c
@@ -85,5 +85,12 @@ __noreturn void __libc_init(uintptr_t *elfdata,
     argv = (char**)(elfdata + 1);
     envp = argv + argc + 1;
 
+    /* The executable may have its own destructors listed in its .fini_array
+     * so we need to ensure that these are called when the program exits
+     * normally.
+     */
+    if (structors->fini_array)
+        __cxa_atexit(__libc_fini,structors->fini_array,NULL);
+
     exit(slingshot(argc, argv, envp));
 }