Fix the C library runtime initialization order.
This allows libc.so to run the C runtime initializer as soon as the
dynamic linker loads the shared library, i.e. before any other initializers
(e.g. static C++ constructors in other shared libraries the executable depends
on).
This also removes the bug where the initializers from the executable itself
were run twice: once by the dynamic linker, and another time by __libc_init
as defined by libc_init_dynamic.c
diff --git a/libc/bionic/libc_init_dynamic.c b/libc/bionic/libc_init_dynamic.c
index 8cf24b4..b8e1078 100644
--- a/libc/bionic/libc_init_dynamic.c
+++ b/libc/bionic/libc_init_dynamic.c
@@ -26,41 +26,74 @@
* 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
+ * - 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.
*/
-/*
- * 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.
- */
-/* #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);
+}
+
__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));
}