1 files changed, 58 insertions, 18 deletions

diff --git a/libc/bionic/libc_init_dynamic.c b/libc/bionic/libc_init_dynamic.c
index 8cf24b4..b479b27 100644
--- a/libc/bionic/libc_init_dynamic.c
+++ b/libc/bionic/libc_init_dynamic.c
@@ -26,41 +26,81 @@
  * SUCH DAMAGE.
  */
 /*
- * libc_init_static.c
+ * libc_init_dynamic.c
  *
- * This function takes the raw data block set up by the ELF loader
- * in the kernel and parses it.  It is invoked by crt0.S which makes
- * any necessary adjustments and passes calls this function using
- * the standard C calling convention.
+ * This source files provides two important functions for dynamic
+ * executables:
  *
- * The arguments are:
- *  uintptr_t *elfdata	 -- The ELF loader data block; usually from the stack.
- *                          Basically a pointer to argc.
- *  void (*onexit)(void) -- Function to install into onexit
- */
-
-/*
- * Several Linux ABIs don't pass the onexit pointer, and the ones that
- * do never use it.  Therefore, unless USE_ONEXIT is defined, we just
- * ignore the onexit pointer.
+ * - a C runtime initializer (__libc_preinit), which is called by
+ *   the dynamic linker when libc.so is loaded. This happens before
+ *   any other initializer (e.g. static C++ constructors in other
+ *   shared libraries the program depends on).
+ *
+ * - a program launch function (__libc_init), which is called after
+ *   all dynamic linking has been performed. Technically, it is called
+ *   from arch-$ARCH/bionic/crtbegin_dynamic.S which is itself called
+ *   by the dynamic linker after all libraries have been loaded and
+ *   initialized.
  */
-/* #define USE_ONEXIT */
 
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <elf.h>
-#include "pthread_internal.h"
 #include "atexit.h"
 #include "libc_init_common.h"
+#include <bionic_tls.h>
 
 extern void malloc_debug_init();
 
+/* We flag the __libc_preinit function as a constructor to ensure
+ * that its address is listed in libc.so's .init_array section.
+ * 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 __libc_prenit(void)
+{
+    /* Read the ELF data pointer form a special slot of the
+     * TLS area, then call __libc_init_common with it.
+     *
+     * Note that:
+     * - we clear the slot so no other initializer sees its value.
+     * - __libc_init_common() will change the TLS area so the old one
+     *   won't be accessible anyway.
+     */
+    void**      tls_area = (void**)__get_tls();
+    unsigned*   elfdata   = tls_area[TLS_SLOT_BIONIC_PREINIT];
+
+    tls_area[TLS_SLOT_BIONIC_PREINIT] = NULL;
+
+    __libc_init_common(elfdata);
+
+#ifdef MALLOC_LEAK_CHECK
+    /* setup malloc leak checker, requires system properties */
+    extern void malloc_debug_init(void);
+    malloc_debug_init();
+#endif
+
+}
+
 __noreturn void __libc_init(uintptr_t *elfdata,
                        void (*onexit)(void),
                        int (*slingshot)(int, char**, char**),
                        structors_array_t const * const structors)
 {
-    __libc_init_common(elfdata, onexit, slingshot, structors, malloc_debug_init);
+    /* 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;
+
+    /* Several Linux ABIs don't pass the onexit pointer, and the ones that
+     * do never use it.  Therefore, we ignore it.
+     */
+
+    exit(slingshot(argc, argv, envp));
 }