Re: [PATCH 1/2] Add framework for tunables

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

On Sat, Jul 2, 2016 at 10:12 AM, Siddhesh Poyarekar
<siddhesh@sourceware.org> wrote:
> The tunables framework allows us to uniformly manage and expose global
> variables inside glibc as switches to users.  README.tunables has
> instructions for glibc developers to add new tunables.
>
> Tunables support can be enabled by passing the --enable-tunables
> configure flag to the configure script.  This patch only adds a
> framework and does not pose any limitations on how tunable values are
> read from the user.  It also adds environment variables used in malloc
> behaviour tweaking to the tunables framework as a PoC of the
> compatibility interface.
>
>         * manual/install.texi: Add --enable-tunables option.
>         * INSTALL: Regenerate.
>         * Makeconfig (CPPFLAGS): Define TOP_NAMESPACE.
>         (before-compile): Generate dl-tunable-list.h early.
>         * config.h.in: Add BUILD_TUNABLES.
>         * config.make.in: Add build-tunables.
>         * configure.ac: Add --enable-tunables option.
>         * configure: Regenerate.
>         * malloc/arena.c [BUILD_TUNABLES]: Include dl-tunables.h.
>         Define TUNABLE_NAMESPACE.
>         (DL_TUNABLE_CALLBACK(set_mallopt_check)): New function.
>         (ptmalloc_init): Set tunable values.
>         * malloc/tst-malloc-usable-static.c: New test case.
>         * csu/init-first.c [BUILD_TUNABLES]: Include dl-tunables.h.
>         (__libc_init_first) [!SHARED]: Initialize tunables for static
>         binaries.
>         * scripts/gen-tunables.awk: New file.
>         * README.tunables: New file.
>         * elf/Versions (ld): Add __tunable_set_val to GLIBC_PRIVATE
>         namespace.
>         * elf/dl-tunable-list.h: New auto-generated file.
>         * elf/dl-tunables.c: New file.
>         * elf/dl-tunables.h: New file.
>         * elf/dl-tunables.list: New file.
>         * elf/dl-tunable-types.h: New file.
>         * elf/rtld.c [BUILD_TUNABLES]: Include dl-tunables.h
>         (process_envvars): Call __tunables_init.
> ---
>  INSTALL                           |   6 ++
>  Makeconfig                        |  16 ++++
>  README.tunables                   |  74 ++++++++++++++++
>  config.h.in                       |   3 +
>  config.make.in                    |   1 +
>  configure                         |  16 ++++
>  configure.ac                      |  10 +++
>  csu/init-first.c                  |   7 ++
>  elf/Makefile                      |   5 ++
>  elf/Versions                      |   3 +
>  elf/dl-tunable-types.h            |  45 ++++++++++
>  elf/dl-tunables.c                 | 172 ++++++++++++++++++++++++++++++++++++++
>  elf/dl-tunables.h                 |  76 +++++++++++++++++
>  elf/dl-tunables.list              |  50 +++++++++++
>  elf/rtld.c                        |   8 ++
>  malloc/Makefile                   |   3 +
>  malloc/arena.c                    |  35 ++++++++
>  malloc/tst-malloc-usable-static.c |   1 +
>  manual/install.texi               |   5 ++
>  scripts/gen-tunables.awk          | 157 ++++++++++++++++++++++++++++++++++
>  20 files changed, 693 insertions(+)
>  create mode 100644 README.tunables
>  create mode 100644 elf/dl-tunable-types.h
>  create mode 100644 elf/dl-tunables.c
>  create mode 100644 elf/dl-tunables.h
>  create mode 100644 elf/dl-tunables.list
>  create mode 100644 malloc/tst-malloc-usable-static.c
>  create mode 100644 scripts/gen-tunables.awk
>


> +/* Same as TUNABLE_SET_VAL, but also set the callback function to __CB and call
> +   it.  */
> +# define TUNABLE_SET_VAL_WITH_CALLBACK(__id,__val,__cb) \
> +({                                                                           \
> +  __tunable_set_val                                                          \
> +   (TUNABLE_ENUM_NAME (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id), (__val),      \
> +    DL_TUNABLE_CALLBACK (__cb));                                             \
> +})
> +
> +/* Namespace sanity for callback functions.  Use this macro to keep the
> +   namespace of the modules clean.  */
> +#define DL_TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
> +#endif

For IFUNC, or any processor specific tunables, a different callback is
needed:

void
ifunc_callback (const char *p)
{
...
}

where p is the string after "GLIBC_IFUNC=".

H.J.