Re: [PATCH] fix static TLS consumption by TLS descriptors

[Will Newton <will dot newton at linaro dot org>]

On 14 May 2014 21:32, Kyle McMartin <kmcmarti@redhat.com> wrote:
> AArch64 presently defaults to use TLS descriptors, as opposed to
> traditional dynamic TLS relocations, and has hit a bug in the copy-pasta
> used in elf_machine_rel{,a} for all TLS descriptor implementations. When
> a program calls dlopen() with R_AARCH64_TLSDESC relocs, we're consuming
> static TLS until it's exhausted (presumably as an optimisation.)
> However, this means that once our static TLS space is consumed,
> attempting to dlopen() any shared object which contain an
> R_AARCH64_TPREL reloc will fail, since we've exhausted all the space.
>
> Instead, always use dynamic TLS for TLS descriptors, which lets us load
> arbitrarily many proper dynamic TLS using shared objects, and allow the
> static TLS fallback only in the non-SHARED case.
>
> This issue is reproducible on x86_64, by specifying -ftls-dialect=gnu2
> when building with gcc. I've written a test for this:
> https://github.com/jkkm/test-tls_desc.git
> Tweak DIALECT to be appropriate, and run ./test-tls_desc.sh, ./main
> and it should fail with:
> % ./test-tls_desc.sh; ./main
> ./tmp16.so: cannot allocate memory in static TLS block
> ./test-tls_desc.sh: line 18: 10141 Aborted                 (core dumped) ./main
>
> 2014-05-14  Kyle McMartin  <kyle@redhat.com>
>
>         * sysdeps/aarch64/dl-machine.h (elf_machine_rela): always
>           allocate dynamic TLS space for TLS descriptors.
>         * sysdeps/x86_64/dl-machine.h (elf_machine_rela): ditto.
>         * sysdeps/arm/dl-machine.h (elf_machine_rel): ditto.
>         * sysdeps/i386/dl-machine.h (elf_machine_rel): ditto.

ChangeLog entries should be sentences, so start with a capital letter.

> --- a/sysdeps/aarch64/dl-machine.h
> +++ b/sysdeps/aarch64/dl-machine.h
> @@ -295,13 +295,12 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
>  # ifndef SHARED
>                 CHECK_STATIC_TLS (map, sym_map);
>  # else
> -               if (!TRY_STATIC_TLS (map, sym_map))
>                   {
>                     td->arg = _dl_make_tlsdesc_dynamic
>                       (sym_map, sym->st_value + reloc->r_addend);
>                     td->entry = _dl_tlsdesc_dynamic;
>                   }
> -               else
> +               if (0)
>  # endif
>  #endif
>                   {
> diff --git a/sysdeps/arm/dl-machine.h b/sysdeps/arm/dl-machine.h
> index 899b256..dcb2127 100644
> --- a/sysdeps/arm/dl-machine.h
> +++ b/sysdeps/arm/dl-machine.h
> @@ -458,13 +458,12 @@ elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
>  #  ifndef SHARED
>                 CHECK_STATIC_TLS (map, sym_map);
>  #  else
> -               if (!TRY_STATIC_TLS (map, sym_map))
>                   {
>                     td->argument.pointer
>                       = _dl_make_tlsdesc_dynamic (sym_map, value);
>                     td->entry = _dl_tlsdesc_dynamic;
>                   }
> -               else
> +               if (0)
>  #  endif
>  # endif
>                 {
> diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h
> index 368bee2..64cf74c 100644
> --- a/sysdeps/i386/dl-machine.h
> +++ b/sysdeps/i386/dl-machine.h
> @@ -394,13 +394,12 @@ elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
>  #  ifndef SHARED
>                 CHECK_STATIC_TLS (map, sym_map);
>  #  else
> -               if (!TRY_STATIC_TLS (map, sym_map))
>                   {
>                     td->arg = _dl_make_tlsdesc_dynamic
>                       (sym_map, sym->st_value + (ElfW(Word))td->arg);
>                     td->entry = _dl_tlsdesc_dynamic;
>                   }
> -               else
> +               if (0)
>  #  endif
>  # endif
>                   {
> diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
> index 8df04a9..67e98d1 100644
> --- a/sysdeps/x86_64/dl-machine.h
> +++ b/sysdeps/x86_64/dl-machine.h
> @@ -359,13 +359,12 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
>  #   ifndef SHARED
>                 CHECK_STATIC_TLS (map, sym_map);
>  #   else
> -               if (!TRY_STATIC_TLS (map, sym_map))
>                   {
>                     td->arg = _dl_make_tlsdesc_dynamic
>                       (sym_map, sym->st_value + reloc->r_addend);
>                     td->entry = _dl_tlsdesc_dynamic;
>                   }
> -               else
> +               if (0)
>  #   endif
>  #  endif
>                   {



-- 
Will Newton
Toolchain Working Group, Linaro