Re: [PATCHv2] Fix float128 IFUNC relocations on ppc64le [BZ #21707]

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

On Sat, Jul 8, 2017 at 11:31 AM, Tulio Magno Quites Machado Filho
<tuliom@linux.vnet.ibm.com> wrote:
> Changes since version 1:
>
>  - Added a testcase.  This is now validating both statically and
>    dynamically linked executables.
>  - Fixed an issue in the $(foreach ..) in sysdeps/powerpc/powerpc64le/Makefile.
>  - Added a comment to csu/libc-start.c
>  - Added a comment to csu/libc-tls.c
>
> -- 8< --
>
> The patch proposed by Peter Bergner [1] to libgc in order to fix
> [BZ #21707] adds a dependency on a symbol provided by the loader,
> forcing the loader to be linked to tests after libgcc was linked.
>
> It also requires to read the thread pointer during IRELA relocations.
>
> Tested on powerpc, powerpc64, powerpc64le, s390x and x86_64.
>
> [1] https://sourceware.org/ml/libc-alpha/2017-06/msg01383.html
>
> 2017-07-08  Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>
>
>         [BZ #21707]
>         * csu/libc-start.c (LIBC_START_MAIN): Perform IREL{,A}
>         relocations after initializing the TCB on statically linked
>         executables..
>         * csu/libc-tls.c (__libc_setup_tls): Add a comment about
>         IREL{,A} relocations.
>         * elf/Makefile (tests-static-normal): Add tst-tlsifunc-static.
>         (tests): Add tst-tlsifunc.
>         * elf/tst-tlsifunc.c: New file.
>         * elf/tst-tlsifunc-static.c: Likewise.
>         * sysdeps/powerpc/powerpc64le/Makefile (f128-loader-link): New
>         variable.
>         [$(subdir) = math] (test-float128% test-ifloat128%): Force
>         linking to the loader after linking to libgcc.
>         [$(subdir) = wcsmbs stdlib] (bug-strtod bug-strtod2 bug-strtod2)
>         (tst-strtod-round tst-wcstod-round tst-strtod6 tst-strrom)
>         (tst-strfrom-locale strfrom-skeleton): Likewise.
> ---
>  csu/libc-start.c                     | 11 +++---
>  csu/libc-tls.c                       |  2 ++
>  elf/Makefile                         |  5 +--
>  elf/tst-tlsifunc-static.c            | 19 +++++++++++
>  elf/tst-tlsifunc.c                   | 66 ++++++++++++++++++++++++++++++++++++
>  sysdeps/powerpc/powerpc64le/Makefile | 10 ++++++
>  6 files changed, 107 insertions(+), 6 deletions(-)
>  create mode 100644 elf/tst-tlsifunc-static.c
>  create mode 100644 elf/tst-tlsifunc.c
>
> diff --git a/csu/libc-start.c b/csu/libc-start.c
> index c2dd159..84b7f99 100644
> --- a/csu/libc-start.c
> +++ b/csu/libc-start.c
> @@ -188,12 +188,15 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
>
>    ARCH_INIT_CPU_FEATURES ();
>
> -  /* Perform IREL{,A} relocations.  */
> -  apply_irel ();
> -
>    /* The stack guard goes into the TCB, so initialize it early.  */
>    __libc_setup_tls ();
>
> +  /* Perform IREL{,A} relocations.
> +     Note: the relocations must happen after TLS initialization so that
> +     IFUNC resolvers can benefit from thread-local storage, e.g. powerpc's
> +     hwcap and platform fields available in the TCB.  */
> +  apply_irel ();
> +
>    /* Set up the stack checker's canary.  */
>    uintptr_t stack_chk_guard = _dl_setup_stack_chk_guard (_dl_random);
>  # ifdef THREAD_SET_STACK_GUARD
> @@ -224,7 +227,7 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
>    __pointer_chk_guard_local = pointer_chk_guard;
>  # endif
>
> -#endif
> +#endif /* !SHARED  */
>

apply_irel should be called as early as possible.  If it doesn't work for
powerpc, we should provide a generic version and powerpc can
provide a special one,  I oppose changing the order in generic file.

H.J.