[PATCH glibc 5/9] glibc: Perform rseq(2) registration at C startup and thread creation (v17)

[Florian Weimer]

* Mathieu Desnoyers via Libc-alpha:

> diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c
> index 1ac66d895d..30466afea0 100644
> --- a/elf/libc_early_init.c
> +++ b/elf/libc_early_init.c
> @@ -18,10 +18,13 @@
>  
>  #include <ctype.h>
>  #include <libc-early-init.h>
> +#include <rseq-internal.h>
>  
>  void
>  __libc_early_init (void)
>  {
>    /* Initialize ctype data.  */
>    __ctype_init ();
> +  /* Register rseq ABI to the kernel.   */
> +  (void) rseq_register_current_thread ();
>  }

I think the registration must be restricted to the primary namespace.
Otherwise, LD_AUDIT will register the area to the secondary libc (in
the audit module), not the primary libc for the entire process.

I think the easiest way to implement this for now is a flag argument
for __libc_early_init (as the upstream __libc_multiple_libcs is not
entirely accurate).  I will submit a patch.