Re: [PATCH 3/5] [PowerPC] Relocate stinfo->main

["H.J. Lu" <hjl.tools@gmail.com>]

On Sun, Jan 23, 2022 at 7:51 PM Alan Modra via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> The previous 2 patches got us to the point of segfaulting when trying
> to transfer to main.
>
> start_addresses in sysdeps/powerpc/powerpc64/start.S is historical
> baggage that should disappear.  Until someone does that, relocating
> stinfo->main by hand is one solution to the fact that the field may be
> unrelocated at the time it is accessed.  This is similar to what is
> done for dynamic tags via the D_PTR macro.  The makefile change is
> needed to pick up elf/dl-static-tls.h from dl-machine.h.
>
> diff --git a/sysdeps/unix/sysv/linux/powerpc/Makefile b/sysdeps/unix/sysv/linux/powerpc/Makefile
> index fc7c29c695..93783cae00 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/Makefile
> +++ b/sysdeps/unix/sysv/linux/powerpc/Makefile
> @@ -27,3 +27,9 @@ tests += $(tests-static)
>  tests += test-gettimebasefreq
>  tests += test-powerpc-linux-sysconf
>  endif
> +
> +ifeq ($(subdir),csu)
> +# to relocate stinfo->main
> +CPPFLAGS-libc-start.o += -I../elf
> +CPPFLAGS-libc-start.op += -I../elf
> +endif
> diff --git a/sysdeps/unix/sysv/linux/powerpc/libc-start.c b/sysdeps/unix/sysv/linux/powerpc/libc-start.c
> index bb97d16145..8f0d3a0eac 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/libc-start.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/libc-start.c
> @@ -23,6 +23,10 @@
>  #ifndef SHARED
>  #include <hwcapinfo.h>
>  #endif
> +#if ENABLE_STATIC_PIE && !defined SHARED
> +/* For elf_machine_load_address.  */
> +#include <dl-machine.h>
> +#endif
>
>  /* The main work is done in the generic function.  */
>  #define LIBC_START_MAIN generic_start_main
> @@ -95,8 +99,15 @@ __libc_start_main_impl (int argc, char **argv,
>    __tcb_parse_hwcap_and_convert_at_platform ();
>  #endif
>
> -  return generic_start_main (stinfo->main, argc, argv, auxvec,
> -                            stinfo->init, stinfo->fini, rtld_fini,
> +  void *main = stinfo->main;
> +#if ENABLE_STATIC_PIE && !defined SHARED
> +  struct link_map *map = _dl_get_dl_main_map ();
> +  if (!map->l_relocated)
> +    main = (char *) main + elf_machine_load_address ();
> +#endif

Can you use __ehdr_start t here, similar to

https://gitlab.com/x86-glibc/glibc/-/commit/1df93c500d0f81d30d1b7e323153512a8768bb72#ffb950808032d5085fdf882753d7bf8889e6a3d7


> +  return generic_start_main (main, argc, argv, auxvec,
> +                            NULL, NULL, rtld_fini,
>                              stack_on_entry);
>  }
>  DEFINE_LIBC_START_MAIN_VERSION
>
> --
> Alan Modra
> Australia Development Lab, IBM



--
H.J.