[PATCH v2] malloc: Improve malloc initialization

[Florian Weimer]

* Wilco Dijkstra:

> diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c
> index 07202317534a4edbd2202c6e45770094cadb67f6..6ab14fb239a02d8da356a1fc5bdb307aabf35705 100644
> --- a/elf/libc_early_init.c
> +++ b/elf/libc_early_init.c
> @@ -29,9 +29,19 @@
>  _Bool __libc_initial;
>  #endif
>  
> +static void __attribute_noinline__
> +myfree (void *p)
> +{
> +  free (p);
> +}
> +
>  void
>  __libc_early_init (_Bool initial)
>  {
> +  /* Initialize malloc using an out-of-range malloc.  */
> +  volatile size_t size = -1;
> +  myfree (malloc (size));
> +
>    /* Initialize ctype data.  */
>    __ctype_init ();
>  

This callos malloc/free from an interposed malloc before its ELF
constructor has run.  I expect this to result in crashes for some
mallocs because they don't expect that we bypass initialization in this
way.  In the future, we might even call __libc_early_init immediately
after libc.so relocation, before other shared objects are relocated.

If we want to pre-initialize malloc, we should explicitly call a
glibc-specific initialization routine from __libc_early_init, using
call_function_static_weak.

Thanks,
Florian