csu: Use ELF constructor instead of _init in libc.so

On !ELF_INITFINI architectures, _init is no longer called by the
dynamic linker.  We can use an ELF constructor instead because the
constructor order does not matter.  (The other constructors are used
to set up libio vtable bypasses and do not depend on this
initialization routine.)

csu/init-first.c

@@ -43,12 +43,11 @@ void
 __libc_init_first (int argc, char **argv, char **envp)
 {
 #ifdef SHARED
-  /* For DSOs we do not need __libc_init_first but instead _init.  */
+  /* For DSOs we do not need __libc_init_first but an ELF constructor.  */
 }
 
-void
-attribute_hidden
-_init (int argc, char **argv, char **envp)
+static void __attribute__ ((constructor))
+_init_first (int argc, char **argv, char **envp)
 {
 #endif
 
@@ -86,8 +85,9 @@ _init (int argc, char **argv, char **envp)
 
 /* This function is defined here so that if this file ever gets into
    ld.so we will get a link error.  Having this file silently included
-   in ld.so causes disaster, because the _init definition above will
-   cause ld.so to gain an init function, which is not a cool thing. */
+   in ld.so causes disaster, because the _init_first definition above
+   will cause ld.so to gain an ELF constructor, which is not a cool
+   thing. */
 
 extern void _dl_start (void) __attribute__ ((noreturn));
 

elf/soinit.c

@@ -20,7 +20,7 @@ run_hooks (void (*const list[]) (void))
     (**list) ();
 }
 
-/* This function will be called from _init in init-first.c.  */
+/* This function will be called from _init_first in init-first.c.  */
 void
 __libc_global_ctors (void)
 {

include/libc-internal.h

@@ -24,7 +24,7 @@
 /* Initialize the `__libc_enable_secure' flag.  */
 extern void __libc_init_secure (void);
 
-/* This function will be called from _init in init-first.c.  */
+/* This function will be called from _init_first in init-first.c.  */
 extern void __libc_global_ctors (void);
 
 /* Discover the tick frequency of the machine if something goes wrong,