[v2] gold: Use autotools pthread macro

Message ID 20180220034420.28567-1-JPEWhacker@gmail.com
State New
Headers show
Series
  • [v2] gold: Use autotools pthread macro
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Commit Message

Joshua Watt Feb. 20, 2018, 3:44 a.m.
The autotools library macro (AX_PTHREAD) is now used to detect if
pthreads is present and multi-threaded linking in gold is automatically
enabled if it is found. This enables multi-threaded gold on platforms
where pthreads is enabled via other methods than just -lpthread (e.g.
MinGW)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>

---
 config/ax_pthread.m4 | 485 +++++++++++++++++++++++++++++++++++++++++++++++++++
 gold/Makefile.am     |  11 +-
 gold/aclocal.m4      |   1 +
 gold/configure.ac    |  38 ++--
 4 files changed, 514 insertions(+), 21 deletions(-)
 create mode 100644 config/ax_pthread.m4

-- 
2.14.3

Comments

Joshua Watt May 11, 2018, 2:31 a.m. | #1
On Mon, Feb 19, 2018 at 9:44 PM, Joshua Watt <jpewhacker@gmail.com> wrote:
> The autotools library macro (AX_PTHREAD) is now used to detect if

> pthreads is present and multi-threaded linking in gold is automatically

> enabled if it is found. This enables multi-threaded gold on platforms

> where pthreads is enabled via other methods than just -lpthread (e.g.

> MinGW)

>

> Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>

> ---

>  config/ax_pthread.m4 | 485 +++++++++++++++++++++++++++++++++++++++++++++++++++

>  gold/Makefile.am     |  11 +-

>  gold/aclocal.m4      |   1 +

>  gold/configure.ac    |  38 ++--

>  4 files changed, 514 insertions(+), 21 deletions(-)

>  create mode 100644 config/ax_pthread.m4

>

> diff --git a/config/ax_pthread.m4 b/config/ax_pthread.m4

> new file mode 100644

> index 0000000000..5fbf9fe0d6

> --- /dev/null

> +++ b/config/ax_pthread.m4

> @@ -0,0 +1,485 @@

> +# ===========================================================================

> +#        https://www.gnu.org/software/autoconf-archive/ax_pthread.html

> +# ===========================================================================

> +#

> +# SYNOPSIS

> +#

> +#   AX_PTHREAD([ACTION-IF-FOUND[, ACTION-IF-NOT-FOUND]])

> +#

> +# DESCRIPTION

> +#

> +#   This macro figures out how to build C programs using POSIX threads. It

> +#   sets the PTHREAD_LIBS output variable to the threads library and linker

> +#   flags, and the PTHREAD_CFLAGS output variable to any special C compiler

> +#   flags that are needed. (The user can also force certain compiler

> +#   flags/libs to be tested by setting these environment variables.)

> +#

> +#   Also sets PTHREAD_CC to any special C compiler that is needed for

> +#   multi-threaded programs (defaults to the value of CC otherwise). (This

> +#   is necessary on AIX to use the special cc_r compiler alias.)

> +#

> +#   NOTE: You are assumed to not only compile your program with these flags,

> +#   but also to link with them as well. For example, you might link with

> +#   $PTHREAD_CC $CFLAGS $PTHREAD_CFLAGS $LDFLAGS ... $PTHREAD_LIBS $LIBS

> +#

> +#   If you are only building threaded programs, you may wish to use these

> +#   variables in your default LIBS, CFLAGS, and CC:

> +#

> +#     LIBS="$PTHREAD_LIBS $LIBS"

> +#     CFLAGS="$CFLAGS $PTHREAD_CFLAGS"

> +#     CC="$PTHREAD_CC"

> +#

> +#   In addition, if the PTHREAD_CREATE_JOINABLE thread-attribute constant

> +#   has a nonstandard name, this macro defines PTHREAD_CREATE_JOINABLE to

> +#   that name (e.g. PTHREAD_CREATE_UNDETACHED on AIX).

> +#

> +#   Also HAVE_PTHREAD_PRIO_INHERIT is defined if pthread is found and the

> +#   PTHREAD_PRIO_INHERIT symbol is defined when compiling with

> +#   PTHREAD_CFLAGS.

> +#

> +#   ACTION-IF-FOUND is a list of shell commands to run if a threads library

> +#   is found, and ACTION-IF-NOT-FOUND is a list of commands to run it if it

> +#   is not found. If ACTION-IF-FOUND is not specified, the default action

> +#   will define HAVE_PTHREAD.

> +#

> +#   Please let the authors know if this macro fails on any platform, or if

> +#   you have any other suggestions or comments. This macro was based on work

> +#   by SGJ on autoconf scripts for FFTW (http://www.fftw.org/) (with help

> +#   from M. Frigo), as well as ac_pthread and hb_pthread macros posted by

> +#   Alejandro Forero Cuervo to the autoconf macro repository. We are also

> +#   grateful for the helpful feedback of numerous users.

> +#

> +#   Updated for Autoconf 2.68 by Daniel Richard G.

> +#

> +# LICENSE

> +#

> +#   Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>

> +#   Copyright (c) 2011 Daniel Richard G. <skunk@iSKUNK.ORG>

> +#

> +#   This program is free software: you can redistribute it and/or modify it

> +#   under the terms of the GNU General Public License as published by the

> +#   Free Software Foundation, either version 3 of the License, or (at your

> +#   option) any later version.

> +#

> +#   This program is distributed in the hope that it will be useful, but

> +#   WITHOUT ANY WARRANTY; without even the implied warranty of

> +#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General

> +#   Public License for more details.

> +#

> +#   You should have received a copy of the GNU General Public License along

> +#   with this program. If not, see <https://www.gnu.org/licenses/>.

> +#

> +#   As a special exception, the respective Autoconf Macro's copyright owner

> +#   gives unlimited permission to copy, distribute and modify the configure

> +#   scripts that are the output of Autoconf when processing the Macro. You

> +#   need not follow the terms of the GNU General Public License when using

> +#   or distributing such scripts, even though portions of the text of the

> +#   Macro appear in them. The GNU General Public License (GPL) does govern

> +#   all other use of the material that constitutes the Autoconf Macro.

> +#

> +#   This special exception to the GPL applies to versions of the Autoconf

> +#   Macro released by the Autoconf Archive. When you make and distribute a

> +#   modified version of the Autoconf Macro, you may extend this special

> +#   exception to the GPL to apply to your modified version as well.

> +

> +#serial 24

> +

> +AU_ALIAS([ACX_PTHREAD], [AX_PTHREAD])

> +AC_DEFUN([AX_PTHREAD], [

> +AC_REQUIRE([AC_CANONICAL_HOST])

> +AC_REQUIRE([AC_PROG_CC])

> +AC_REQUIRE([AC_PROG_SED])

> +AC_LANG_PUSH([C])

> +ax_pthread_ok=no

> +

> +# We used to check for pthread.h first, but this fails if pthread.h

> +# requires special compiler flags (e.g. on Tru64 or Sequent).

> +# It gets checked for in the link test anyway.

> +

> +# First of all, check if the user has set any of the PTHREAD_LIBS,

> +# etcetera environment variables, and if threads linking works using

> +# them:

> +if test "x$PTHREAD_CFLAGS$PTHREAD_LIBS" != "x"; then

> +        ax_pthread_save_CC="$CC"

> +        ax_pthread_save_CFLAGS="$CFLAGS"

> +        ax_pthread_save_LIBS="$LIBS"

> +        AS_IF([test "x$PTHREAD_CC" != "x"], [CC="$PTHREAD_CC"])

> +        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"

> +        LIBS="$PTHREAD_LIBS $LIBS"

> +        AC_MSG_CHECKING([for pthread_join using $CC $PTHREAD_CFLAGS $PTHREAD_LIBS])

> +        AC_LINK_IFELSE([AC_LANG_CALL([], [pthread_join])], [ax_pthread_ok=yes])

> +        AC_MSG_RESULT([$ax_pthread_ok])

> +        if test "x$ax_pthread_ok" = "xno"; then

> +                PTHREAD_LIBS=""

> +                PTHREAD_CFLAGS=""

> +        fi

> +        CC="$ax_pthread_save_CC"

> +        CFLAGS="$ax_pthread_save_CFLAGS"

> +        LIBS="$ax_pthread_save_LIBS"

> +fi

> +

> +# We must check for the threads library under a number of different

> +# names; the ordering is very important because some systems

> +# (e.g. DEC) have both -lpthread and -lpthreads, where one of the

> +# libraries is broken (non-POSIX).

> +

> +# Create a list of thread flags to try.  Items starting with a "-" are

> +# C compiler flags, and other items are library names, except for "none"

> +# which indicates that we try without any flags at all, and "pthread-config"

> +# which is a program returning the flags for the Pth emulation library.

> +

> +ax_pthread_flags="pthreads none -Kthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"

> +

> +# The ordering *is* (sometimes) important.  Some notes on the

> +# individual items follow:

> +

> +# pthreads: AIX (must check this before -lpthread)

> +# none: in case threads are in libc; should be tried before -Kthread and

> +#       other compiler flags to prevent continual compiler warnings

> +# -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)

> +# -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads), Tru64

> +#           (Note: HP C rejects this with "bad form for `-t' option")

> +# -pthreads: Solaris/gcc (Note: HP C also rejects)

> +# -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it

> +#      doesn't hurt to check since this sometimes defines pthreads and

> +#      -D_REENTRANT too), HP C (must be checked before -lpthread, which

> +#      is present but should not be used directly; and before -mthreads,

> +#      because the compiler interprets this as "-mt" + "-hreads")

> +# -mthreads: Mingw32/gcc, Lynx/gcc

> +# pthread: Linux, etcetera

> +# --thread-safe: KAI C++

> +# pthread-config: use pthread-config program (for GNU Pth library)

> +

> +case $host_os in

> +

> +        freebsd*)

> +

> +        # -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)

> +        # lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)

> +

> +        ax_pthread_flags="-kthread lthread $ax_pthread_flags"

> +        ;;

> +

> +        hpux*)

> +

> +        # From the cc(1) man page: "[-mt] Sets various -D flags to enable

> +        # multi-threading and also sets -lpthread."

> +

> +        ax_pthread_flags="-mt -pthread pthread $ax_pthread_flags"

> +        ;;

> +

> +        openedition*)

> +

> +        # IBM z/OS requires a feature-test macro to be defined in order to

> +        # enable POSIX threads at all, so give the user a hint if this is

> +        # not set. (We don't define these ourselves, as they can affect

> +        # other portions of the system API in unpredictable ways.)

> +

> +        AC_EGREP_CPP([AX_PTHREAD_ZOS_MISSING],

> +            [

> +#            if !defined(_OPEN_THREADS) && !defined(_UNIX03_THREADS)

> +             AX_PTHREAD_ZOS_MISSING

> +#            endif

> +            ],

> +            [AC_MSG_WARN([IBM z/OS requires -D_OPEN_THREADS or -D_UNIX03_THREADS to enable pthreads support.])])

> +        ;;

> +

> +        solaris*)

> +

> +        # On Solaris (at least, for some versions), libc contains stubbed

> +        # (non-functional) versions of the pthreads routines, so link-based

> +        # tests will erroneously succeed. (N.B.: The stubs are missing

> +        # pthread_cleanup_push, or rather a function called by this macro,

> +        # so we could check for that, but who knows whether they'll stub

> +        # that too in a future libc.)  So we'll check first for the

> +        # standard Solaris way of linking pthreads (-mt -lpthread).

> +

> +        ax_pthread_flags="-mt,pthread pthread $ax_pthread_flags"

> +        ;;

> +esac

> +

> +# GCC generally uses -pthread, or -pthreads on some platforms (e.g. SPARC)

> +

> +AS_IF([test "x$GCC" = "xyes"],

> +      [ax_pthread_flags="-pthread -pthreads $ax_pthread_flags"])

> +

> +# The presence of a feature test macro requesting re-entrant function

> +# definitions is, on some systems, a strong hint that pthreads support is

> +# correctly enabled

> +

> +case $host_os in

> +        darwin* | hpux* | linux* | osf* | solaris*)

> +        ax_pthread_check_macro="_REENTRANT"

> +        ;;

> +

> +        aix*)

> +        ax_pthread_check_macro="_THREAD_SAFE"

> +        ;;

> +

> +        *)

> +        ax_pthread_check_macro="--"

> +        ;;

> +esac

> +AS_IF([test "x$ax_pthread_check_macro" = "x--"],

> +      [ax_pthread_check_cond=0],

> +      [ax_pthread_check_cond="!defined($ax_pthread_check_macro)"])

> +

> +# Are we compiling with Clang?

> +

> +AC_CACHE_CHECK([whether $CC is Clang],

> +    [ax_cv_PTHREAD_CLANG],

> +    [ax_cv_PTHREAD_CLANG=no

> +     # Note that Autoconf sets GCC=yes for Clang as well as GCC

> +     if test "x$GCC" = "xyes"; then

> +        AC_EGREP_CPP([AX_PTHREAD_CC_IS_CLANG],

> +            [/* Note: Clang 2.7 lacks __clang_[a-z]+__ */

> +#            if defined(__clang__) && defined(__llvm__)

> +             AX_PTHREAD_CC_IS_CLANG

> +#            endif

> +            ],

> +            [ax_cv_PTHREAD_CLANG=yes])

> +     fi

> +    ])

> +ax_pthread_clang="$ax_cv_PTHREAD_CLANG"

> +

> +ax_pthread_clang_warning=no

> +

> +# Clang needs special handling, because older versions handle the -pthread

> +# option in a rather... idiosyncratic way

> +

> +if test "x$ax_pthread_clang" = "xyes"; then

> +

> +        # Clang takes -pthread; it has never supported any other flag

> +

> +        # (Note 1: This will need to be revisited if a system that Clang

> +        # supports has POSIX threads in a separate library.  This tends not

> +        # to be the way of modern systems, but it's conceivable.)

> +

> +        # (Note 2: On some systems, notably Darwin, -pthread is not needed

> +        # to get POSIX threads support; the API is always present and

> +        # active.  We could reasonably leave PTHREAD_CFLAGS empty.  But

> +        # -pthread does define _REENTRANT, and while the Darwin headers

> +        # ignore this macro, third-party headers might not.)

> +

> +        PTHREAD_CFLAGS="-pthread"

> +        PTHREAD_LIBS=

> +

> +        ax_pthread_ok=yes

> +

> +        # However, older versions of Clang make a point of warning the user

> +        # that, in an invocation where only linking and no compilation is

> +        # taking place, the -pthread option has no effect ("argument unused

> +        # during compilation").  They expect -pthread to be passed in only

> +        # when source code is being compiled.

> +        #

> +        # Problem is, this is at odds with the way Automake and most other

> +        # C build frameworks function, which is that the same flags used in

> +        # compilation (CFLAGS) are also used in linking.  Many systems

> +        # supported by AX_PTHREAD require exactly this for POSIX threads

> +        # support, and in fact it is often not straightforward to specify a

> +        # flag that is used only in the compilation phase and not in

> +        # linking.  Such a scenario is extremely rare in practice.

> +        #

> +        # Even though use of the -pthread flag in linking would only print

> +        # a warning, this can be a nuisance for well-run software projects

> +        # that build with -Werror.  So if the active version of Clang has

> +        # this misfeature, we search for an option to squash it.

> +

> +        AC_CACHE_CHECK([whether Clang needs flag to prevent "argument unused" warning when linking with -pthread],

> +            [ax_cv_PTHREAD_CLANG_NO_WARN_FLAG],

> +            [ax_cv_PTHREAD_CLANG_NO_WARN_FLAG=unknown

> +             # Create an alternate version of $ac_link that compiles and

> +             # links in two steps (.c -> .o, .o -> exe) instead of one

> +             # (.c -> exe), because the warning occurs only in the second

> +             # step

> +             ax_pthread_save_ac_link="$ac_link"

> +             ax_pthread_sed='s/conftest\.\$ac_ext/conftest.$ac_objext/g'

> +             ax_pthread_link_step=`$as_echo "$ac_link" | sed "$ax_pthread_sed"`

> +             ax_pthread_2step_ac_link="($ac_compile) && (echo ==== >&5) && ($ax_pthread_link_step)"

> +             ax_pthread_save_CFLAGS="$CFLAGS"

> +             for ax_pthread_try in '' -Qunused-arguments -Wno-unused-command-line-argument unknown; do

> +                AS_IF([test "x$ax_pthread_try" = "xunknown"], [break])

> +                CFLAGS="-Werror -Wunknown-warning-option $ax_pthread_try -pthread $ax_pthread_save_CFLAGS"

> +                ac_link="$ax_pthread_save_ac_link"

> +                AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],

> +                    [ac_link="$ax_pthread_2step_ac_link"

> +                     AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],

> +                         [break])

> +                    ])

> +             done

> +             ac_link="$ax_pthread_save_ac_link"

> +             CFLAGS="$ax_pthread_save_CFLAGS"

> +             AS_IF([test "x$ax_pthread_try" = "x"], [ax_pthread_try=no])

> +             ax_cv_PTHREAD_CLANG_NO_WARN_FLAG="$ax_pthread_try"

> +            ])

> +

> +        case "$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG" in

> +                no | unknown) ;;

> +                *) PTHREAD_CFLAGS="$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG $PTHREAD_CFLAGS" ;;

> +        esac

> +

> +fi # $ax_pthread_clang = yes

> +

> +if test "x$ax_pthread_ok" = "xno"; then

> +for ax_pthread_try_flag in $ax_pthread_flags; do

> +

> +        case $ax_pthread_try_flag in

> +                none)

> +                AC_MSG_CHECKING([whether pthreads work without any flags])

> +                ;;

> +

> +                -mt,pthread)

> +                AC_MSG_CHECKING([whether pthreads work with -mt -lpthread])

> +                PTHREAD_CFLAGS="-mt"

> +                PTHREAD_LIBS="-lpthread"

> +                ;;

> +

> +                -*)

> +                AC_MSG_CHECKING([whether pthreads work with $ax_pthread_try_flag])

> +                PTHREAD_CFLAGS="$ax_pthread_try_flag"

> +                ;;

> +

> +                pthread-config)

> +                AC_CHECK_PROG([ax_pthread_config], [pthread-config], [yes], [no])

> +                AS_IF([test "x$ax_pthread_config" = "xno"], [continue])

> +                PTHREAD_CFLAGS="`pthread-config --cflags`"

> +                PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"

> +                ;;

> +

> +                *)

> +                AC_MSG_CHECKING([for the pthreads library -l$ax_pthread_try_flag])

> +                PTHREAD_LIBS="-l$ax_pthread_try_flag"

> +                ;;

> +        esac

> +

> +        ax_pthread_save_CFLAGS="$CFLAGS"

> +        ax_pthread_save_LIBS="$LIBS"

> +        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"

> +        LIBS="$PTHREAD_LIBS $LIBS"

> +

> +        # Check for various functions.  We must include pthread.h,

> +        # since some functions may be macros.  (On the Sequent, we

> +        # need a special flag -Kthread to make this header compile.)

> +        # We check for pthread_join because it is in -lpthread on IRIX

> +        # while pthread_create is in libc.  We check for pthread_attr_init

> +        # due to DEC craziness with -lpthreads.  We check for

> +        # pthread_cleanup_push because it is one of the few pthread

> +        # functions on Solaris that doesn't have a non-functional libc stub.

> +        # We try pthread_create on general principles.

> +

> +        AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>

> +#                       if $ax_pthread_check_cond

> +#                        error "$ax_pthread_check_macro must be defined"

> +#                       endif

> +                        static void routine(void *a) { a = 0; }

> +                        static void *start_routine(void *a) { return a; }],

> +                       [pthread_t th; pthread_attr_t attr;

> +                        pthread_create(&th, 0, start_routine, 0);

> +                        pthread_join(th, 0);

> +                        pthread_attr_init(&attr);

> +                        pthread_cleanup_push(routine, 0);

> +                        pthread_cleanup_pop(0) /* ; */])],

> +            [ax_pthread_ok=yes],

> +            [])

> +

> +        CFLAGS="$ax_pthread_save_CFLAGS"

> +        LIBS="$ax_pthread_save_LIBS"

> +

> +        AC_MSG_RESULT([$ax_pthread_ok])

> +        AS_IF([test "x$ax_pthread_ok" = "xyes"], [break])

> +

> +        PTHREAD_LIBS=""

> +        PTHREAD_CFLAGS=""

> +done

> +fi

> +

> +# Various other checks:

> +if test "x$ax_pthread_ok" = "xyes"; then

> +        ax_pthread_save_CFLAGS="$CFLAGS"

> +        ax_pthread_save_LIBS="$LIBS"

> +        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"

> +        LIBS="$PTHREAD_LIBS $LIBS"

> +

> +        # Detect AIX lossage: JOINABLE attribute is called UNDETACHED.

> +        AC_CACHE_CHECK([for joinable pthread attribute],

> +            [ax_cv_PTHREAD_JOINABLE_ATTR],

> +            [ax_cv_PTHREAD_JOINABLE_ATTR=unknown

> +             for ax_pthread_attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do

> +                 AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>],

> +                                                 [int attr = $ax_pthread_attr; return attr /* ; */])],

> +                                [ax_cv_PTHREAD_JOINABLE_ATTR=$ax_pthread_attr; break],

> +                                [])

> +             done

> +            ])

> +        AS_IF([test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xunknown" && \

> +               test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xPTHREAD_CREATE_JOINABLE" && \

> +               test "x$ax_pthread_joinable_attr_defined" != "xyes"],

> +              [AC_DEFINE_UNQUOTED([PTHREAD_CREATE_JOINABLE],

> +                                  [$ax_cv_PTHREAD_JOINABLE_ATTR],

> +                                  [Define to necessary symbol if this constant

> +                                   uses a non-standard name on your system.])

> +               ax_pthread_joinable_attr_defined=yes

> +              ])

> +

> +        AC_CACHE_CHECK([whether more special flags are required for pthreads],

> +            [ax_cv_PTHREAD_SPECIAL_FLAGS],

> +            [ax_cv_PTHREAD_SPECIAL_FLAGS=no

> +             case $host_os in

> +             solaris*)

> +             ax_cv_PTHREAD_SPECIAL_FLAGS="-D_POSIX_PTHREAD_SEMANTICS"

> +             ;;

> +             esac

> +            ])

> +        AS_IF([test "x$ax_cv_PTHREAD_SPECIAL_FLAGS" != "xno" && \

> +               test "x$ax_pthread_special_flags_added" != "xyes"],

> +              [PTHREAD_CFLAGS="$ax_cv_PTHREAD_SPECIAL_FLAGS $PTHREAD_CFLAGS"

> +               ax_pthread_special_flags_added=yes])

> +

> +        AC_CACHE_CHECK([for PTHREAD_PRIO_INHERIT],

> +            [ax_cv_PTHREAD_PRIO_INHERIT],

> +            [AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <pthread.h>]],

> +                                             [[int i = PTHREAD_PRIO_INHERIT;]])],

> +                            [ax_cv_PTHREAD_PRIO_INHERIT=yes],

> +                            [ax_cv_PTHREAD_PRIO_INHERIT=no])

> +            ])

> +        AS_IF([test "x$ax_cv_PTHREAD_PRIO_INHERIT" = "xyes" && \

> +               test "x$ax_pthread_prio_inherit_defined" != "xyes"],

> +              [AC_DEFINE([HAVE_PTHREAD_PRIO_INHERIT], [1], [Have PTHREAD_PRIO_INHERIT.])

> +               ax_pthread_prio_inherit_defined=yes

> +              ])

> +

> +        CFLAGS="$ax_pthread_save_CFLAGS"

> +        LIBS="$ax_pthread_save_LIBS"

> +

> +        # More AIX lossage: compile with *_r variant

> +        if test "x$GCC" != "xyes"; then

> +            case $host_os in

> +                aix*)

> +                AS_CASE(["x/$CC"],

> +                    [x*/c89|x*/c89_128|x*/c99|x*/c99_128|x*/cc|x*/cc128|x*/xlc|x*/xlc_v6|x*/xlc128|x*/xlc128_v6],

> +                    [#handle absolute path differently from PATH based program lookup

> +                     AS_CASE(["x$CC"],

> +                         [x/*],

> +                         [AS_IF([AS_EXECUTABLE_P([${CC}_r])],[PTHREAD_CC="${CC}_r"])],

> +                         [AC_CHECK_PROGS([PTHREAD_CC],[${CC}_r],[$CC])])])

> +                ;;

> +            esac

> +        fi

> +fi

> +

> +test -n "$PTHREAD_CC" || PTHREAD_CC="$CC"

> +

> +AC_SUBST([PTHREAD_LIBS])

> +AC_SUBST([PTHREAD_CFLAGS])

> +AC_SUBST([PTHREAD_CC])

> +

> +# Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:

> +if test "x$ax_pthread_ok" = "xyes"; then

> +        ifelse([$1],,[AC_DEFINE([HAVE_PTHREAD],[1],[Define if you have POSIX threads libraries and header files.])],[$1])

> +        :

> +else

> +        ax_pthread_ok=no

> +        $2

> +fi

> +AC_LANG_POP

> +])dnl AX_PTHREAD

> diff --git a/gold/Makefile.am b/gold/Makefile.am

> index 675deecb47..f87067aab4 100644

> --- a/gold/Makefile.am

> +++ b/gold/Makefile.am

> @@ -31,8 +31,11 @@ ACLOCAL_AMFLAGS = -I ../bfd -I ../config

>  ZLIB = @zlibdir@ -lz

>  ZLIBINC = @zlibinc@

>

> -AM_CFLAGS = $(WARN_CFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC)

> -AM_CXXFLAGS = $(WARN_CXXFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC)

> +THREADFLAGS = @PTHREAD_CFLAGS@

> +THREADLIBS = @PTHREAD_LIBS@

> +

> +AM_CFLAGS = $(WARN_CFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC) $(THREADFLAGS)

> +AM_CXXFLAGS = $(WARN_CXXFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC) $(THREADFLAGS)

>

>  AM_CPPFLAGS = \

>         -I$(srcdir) -I$(srcdir)/../include -I$(srcdir)/../elfcpp \

> @@ -46,10 +49,6 @@ if PLUGINS

>  LIBDL = @DLOPEN_LIBS@

>  endif

>

> -if THREADS

> -THREADSLIB = -lpthread

> -endif

> -

>  AM_YFLAGS = -d

>

>  # Automake 1.10+ disables lex and yacc output file regeneration if

> diff --git a/gold/aclocal.m4 b/gold/aclocal.m4

> index 47cb21fc5a..2f34365173 100644

> --- a/gold/aclocal.m4

> +++ b/gold/aclocal.m4

> @@ -1000,6 +1000,7 @@ AC_SUBST([am__tar])

>  AC_SUBST([am__untar])

>  ]) # _AM_PROG_TAR

>

> +m4_include([../config/ax_pthread.m4])

>  m4_include([../config/depstand.m4])

>  m4_include([../config/gettext-sister.m4])

>  m4_include([../config/lcmessage.m4])

> diff --git a/gold/configure.ac b/gold/configure.ac

> index 5ba43f2f95..bd21335a17 100644

> --- a/gold/configure.ac

> +++ b/gold/configure.ac

> @@ -85,21 +85,6 @@ AC_ARG_ENABLE(gold,

>  AC_SUBST(install_as_default)

>  AC_SUBST(installed_linker)

>

> -dnl For now threads are a configure time option.

> -AC_ARG_ENABLE([threads],

> -[  --enable-threads        multi-threaded linking],

> -[case "${enableval}" in

> -  yes | "") threads=yes ;;

> -  no) threads=no ;;

> -  *) threads=yes ;;

> - esac],

> -[threads=no])

> -if test "$threads" = "yes"; then

> -  AC_DEFINE(ENABLE_THREADS, 1,

> -           [Define to do multi-threaded linking])

> -fi

> -AM_CONDITIONAL(THREADS, test "$threads" = "yes")

> -

>  AC_ARG_ENABLE([plugins],

>  [  --enable-plugins        linker plugins],

>  [case "${enableval}" in

> @@ -570,6 +555,29 @@ fi

>  # Link in zlib if we can.  This allows us to write compressed sections.

>  AM_ZLIB

>

> +

> +AC_ARG_ENABLE([threads],

> +[[  --enable-threads[=ARG]  multi-threaded linking [ARG={auto,yes,no}]]],

> +[case "${enableval}" in

> +  yes | "") threads=yes ;;

> +  no) threads=no ;;

> +  auto) threads=auto ;;

> +  *) threads=yes ;;

> + esac],

> +[threads=auto])

> +

> +if test "$threads" = "yes"; then

> +  AX_PTHREAD([thread=yes], AC_MSG_ERROR([pthread not found]))

> +elif test "$threads" = "auto"; then

> +  AX_PTHREAD([threads=yes], [threads=no])

> +fi

> +

> +if test "$threads" = "yes"; then

> +  AC_DEFINE(ENABLE_THREADS, 1,

> +           [Define to do multi-threaded linking])

> +fi

> +AM_CONDITIONAL(THREADS, test "$threads" = "yes")

> +

>  dnl We have to check these in C, not C++, because autoconf generates

>  dnl tests which have no type information, and current glibc provides

>  dnl multiple declarations of functions like basename when compiling

> --

> 2.14.3

>


GCC accepted the ax_pthread.m4 macro, so this should be ready now.
See: https://gcc.gnu.org/ml/gcc-patches/2018-05/msg00414.html

Patch

diff --git a/config/ax_pthread.m4 b/config/ax_pthread.m4
new file mode 100644
index 0000000000..5fbf9fe0d6
--- /dev/null
+++ b/config/ax_pthread.m4
@@ -0,0 +1,485 @@ 
+# ===========================================================================
+#        https://www.gnu.org/software/autoconf-archive/ax_pthread.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_PTHREAD([ACTION-IF-FOUND[, ACTION-IF-NOT-FOUND]])
+#
+# DESCRIPTION
+#
+#   This macro figures out how to build C programs using POSIX threads. It
+#   sets the PTHREAD_LIBS output variable to the threads library and linker
+#   flags, and the PTHREAD_CFLAGS output variable to any special C compiler
+#   flags that are needed. (The user can also force certain compiler
+#   flags/libs to be tested by setting these environment variables.)
+#
+#   Also sets PTHREAD_CC to any special C compiler that is needed for
+#   multi-threaded programs (defaults to the value of CC otherwise). (This
+#   is necessary on AIX to use the special cc_r compiler alias.)
+#
+#   NOTE: You are assumed to not only compile your program with these flags,
+#   but also to link with them as well. For example, you might link with
+#   $PTHREAD_CC $CFLAGS $PTHREAD_CFLAGS $LDFLAGS ... $PTHREAD_LIBS $LIBS
+#
+#   If you are only building threaded programs, you may wish to use these
+#   variables in your default LIBS, CFLAGS, and CC:
+#
+#     LIBS="$PTHREAD_LIBS $LIBS"
+#     CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+#     CC="$PTHREAD_CC"
+#
+#   In addition, if the PTHREAD_CREATE_JOINABLE thread-attribute constant
+#   has a nonstandard name, this macro defines PTHREAD_CREATE_JOINABLE to
+#   that name (e.g. PTHREAD_CREATE_UNDETACHED on AIX).
+#
+#   Also HAVE_PTHREAD_PRIO_INHERIT is defined if pthread is found and the
+#   PTHREAD_PRIO_INHERIT symbol is defined when compiling with
+#   PTHREAD_CFLAGS.
+#
+#   ACTION-IF-FOUND is a list of shell commands to run if a threads library
+#   is found, and ACTION-IF-NOT-FOUND is a list of commands to run it if it
+#   is not found. If ACTION-IF-FOUND is not specified, the default action
+#   will define HAVE_PTHREAD.
+#
+#   Please let the authors know if this macro fails on any platform, or if
+#   you have any other suggestions or comments. This macro was based on work
+#   by SGJ on autoconf scripts for FFTW (http://www.fftw.org/) (with help
+#   from M. Frigo), as well as ac_pthread and hb_pthread macros posted by
+#   Alejandro Forero Cuervo to the autoconf macro repository. We are also
+#   grateful for the helpful feedback of numerous users.
+#
+#   Updated for Autoconf 2.68 by Daniel Richard G.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
+#   Copyright (c) 2011 Daniel Richard G. <skunk@iSKUNK.ORG>
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 24
+
+AU_ALIAS([ACX_PTHREAD], [AX_PTHREAD])
+AC_DEFUN([AX_PTHREAD], [
+AC_REQUIRE([AC_CANONICAL_HOST])
+AC_REQUIRE([AC_PROG_CC])
+AC_REQUIRE([AC_PROG_SED])
+AC_LANG_PUSH([C])
+ax_pthread_ok=no
+
+# We used to check for pthread.h first, but this fails if pthread.h
+# requires special compiler flags (e.g. on Tru64 or Sequent).
+# It gets checked for in the link test anyway.
+
+# First of all, check if the user has set any of the PTHREAD_LIBS,
+# etcetera environment variables, and if threads linking works using
+# them:
+if test "x$PTHREAD_CFLAGS$PTHREAD_LIBS" != "x"; then
+        ax_pthread_save_CC="$CC"
+        ax_pthread_save_CFLAGS="$CFLAGS"
+        ax_pthread_save_LIBS="$LIBS"
+        AS_IF([test "x$PTHREAD_CC" != "x"], [CC="$PTHREAD_CC"])
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+        AC_MSG_CHECKING([for pthread_join using $CC $PTHREAD_CFLAGS $PTHREAD_LIBS])
+        AC_LINK_IFELSE([AC_LANG_CALL([], [pthread_join])], [ax_pthread_ok=yes])
+        AC_MSG_RESULT([$ax_pthread_ok])
+        if test "x$ax_pthread_ok" = "xno"; then
+                PTHREAD_LIBS=""
+                PTHREAD_CFLAGS=""
+        fi
+        CC="$ax_pthread_save_CC"
+        CFLAGS="$ax_pthread_save_CFLAGS"
+        LIBS="$ax_pthread_save_LIBS"
+fi
+
+# We must check for the threads library under a number of different
+# names; the ordering is very important because some systems
+# (e.g. DEC) have both -lpthread and -lpthreads, where one of the
+# libraries is broken (non-POSIX).
+
+# Create a list of thread flags to try.  Items starting with a "-" are
+# C compiler flags, and other items are library names, except for "none"
+# which indicates that we try without any flags at all, and "pthread-config"
+# which is a program returning the flags for the Pth emulation library.
+
+ax_pthread_flags="pthreads none -Kthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"
+
+# The ordering *is* (sometimes) important.  Some notes on the
+# individual items follow:
+
+# pthreads: AIX (must check this before -lpthread)
+# none: in case threads are in libc; should be tried before -Kthread and
+#       other compiler flags to prevent continual compiler warnings
+# -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
+# -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads), Tru64
+#           (Note: HP C rejects this with "bad form for `-t' option")
+# -pthreads: Solaris/gcc (Note: HP C also rejects)
+# -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
+#      doesn't hurt to check since this sometimes defines pthreads and
+#      -D_REENTRANT too), HP C (must be checked before -lpthread, which
+#      is present but should not be used directly; and before -mthreads,
+#      because the compiler interprets this as "-mt" + "-hreads")
+# -mthreads: Mingw32/gcc, Lynx/gcc
+# pthread: Linux, etcetera
+# --thread-safe: KAI C++
+# pthread-config: use pthread-config program (for GNU Pth library)
+
+case $host_os in
+
+        freebsd*)
+
+        # -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
+        # lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)
+
+        ax_pthread_flags="-kthread lthread $ax_pthread_flags"
+        ;;
+
+        hpux*)
+
+        # From the cc(1) man page: "[-mt] Sets various -D flags to enable
+        # multi-threading and also sets -lpthread."
+
+        ax_pthread_flags="-mt -pthread pthread $ax_pthread_flags"
+        ;;
+
+        openedition*)
+
+        # IBM z/OS requires a feature-test macro to be defined in order to
+        # enable POSIX threads at all, so give the user a hint if this is
+        # not set. (We don't define these ourselves, as they can affect
+        # other portions of the system API in unpredictable ways.)
+
+        AC_EGREP_CPP([AX_PTHREAD_ZOS_MISSING],
+            [
+#            if !defined(_OPEN_THREADS) && !defined(_UNIX03_THREADS)
+             AX_PTHREAD_ZOS_MISSING
+#            endif
+            ],
+            [AC_MSG_WARN([IBM z/OS requires -D_OPEN_THREADS or -D_UNIX03_THREADS to enable pthreads support.])])
+        ;;
+
+        solaris*)
+
+        # On Solaris (at least, for some versions), libc contains stubbed
+        # (non-functional) versions of the pthreads routines, so link-based
+        # tests will erroneously succeed. (N.B.: The stubs are missing
+        # pthread_cleanup_push, or rather a function called by this macro,
+        # so we could check for that, but who knows whether they'll stub
+        # that too in a future libc.)  So we'll check first for the
+        # standard Solaris way of linking pthreads (-mt -lpthread).
+
+        ax_pthread_flags="-mt,pthread pthread $ax_pthread_flags"
+        ;;
+esac
+
+# GCC generally uses -pthread, or -pthreads on some platforms (e.g. SPARC)
+
+AS_IF([test "x$GCC" = "xyes"],
+      [ax_pthread_flags="-pthread -pthreads $ax_pthread_flags"])
+
+# The presence of a feature test macro requesting re-entrant function
+# definitions is, on some systems, a strong hint that pthreads support is
+# correctly enabled
+
+case $host_os in
+        darwin* | hpux* | linux* | osf* | solaris*)
+        ax_pthread_check_macro="_REENTRANT"
+        ;;
+
+        aix*)
+        ax_pthread_check_macro="_THREAD_SAFE"
+        ;;
+
+        *)
+        ax_pthread_check_macro="--"
+        ;;
+esac
+AS_IF([test "x$ax_pthread_check_macro" = "x--"],
+      [ax_pthread_check_cond=0],
+      [ax_pthread_check_cond="!defined($ax_pthread_check_macro)"])
+
+# Are we compiling with Clang?
+
+AC_CACHE_CHECK([whether $CC is Clang],
+    [ax_cv_PTHREAD_CLANG],
+    [ax_cv_PTHREAD_CLANG=no
+     # Note that Autoconf sets GCC=yes for Clang as well as GCC
+     if test "x$GCC" = "xyes"; then
+        AC_EGREP_CPP([AX_PTHREAD_CC_IS_CLANG],
+            [/* Note: Clang 2.7 lacks __clang_[a-z]+__ */
+#            if defined(__clang__) && defined(__llvm__)
+             AX_PTHREAD_CC_IS_CLANG
+#            endif
+            ],
+            [ax_cv_PTHREAD_CLANG=yes])
+     fi
+    ])
+ax_pthread_clang="$ax_cv_PTHREAD_CLANG"
+
+ax_pthread_clang_warning=no
+
+# Clang needs special handling, because older versions handle the -pthread
+# option in a rather... idiosyncratic way
+
+if test "x$ax_pthread_clang" = "xyes"; then
+
+        # Clang takes -pthread; it has never supported any other flag
+
+        # (Note 1: This will need to be revisited if a system that Clang
+        # supports has POSIX threads in a separate library.  This tends not
+        # to be the way of modern systems, but it's conceivable.)
+
+        # (Note 2: On some systems, notably Darwin, -pthread is not needed
+        # to get POSIX threads support; the API is always present and
+        # active.  We could reasonably leave PTHREAD_CFLAGS empty.  But
+        # -pthread does define _REENTRANT, and while the Darwin headers
+        # ignore this macro, third-party headers might not.)
+
+        PTHREAD_CFLAGS="-pthread"
+        PTHREAD_LIBS=
+
+        ax_pthread_ok=yes
+
+        # However, older versions of Clang make a point of warning the user
+        # that, in an invocation where only linking and no compilation is
+        # taking place, the -pthread option has no effect ("argument unused
+        # during compilation").  They expect -pthread to be passed in only
+        # when source code is being compiled.
+        #
+        # Problem is, this is at odds with the way Automake and most other
+        # C build frameworks function, which is that the same flags used in
+        # compilation (CFLAGS) are also used in linking.  Many systems
+        # supported by AX_PTHREAD require exactly this for POSIX threads
+        # support, and in fact it is often not straightforward to specify a
+        # flag that is used only in the compilation phase and not in
+        # linking.  Such a scenario is extremely rare in practice.
+        #
+        # Even though use of the -pthread flag in linking would only print
+        # a warning, this can be a nuisance for well-run software projects
+        # that build with -Werror.  So if the active version of Clang has
+        # this misfeature, we search for an option to squash it.
+
+        AC_CACHE_CHECK([whether Clang needs flag to prevent "argument unused" warning when linking with -pthread],
+            [ax_cv_PTHREAD_CLANG_NO_WARN_FLAG],
+            [ax_cv_PTHREAD_CLANG_NO_WARN_FLAG=unknown
+             # Create an alternate version of $ac_link that compiles and
+             # links in two steps (.c -> .o, .o -> exe) instead of one
+             # (.c -> exe), because the warning occurs only in the second
+             # step
+             ax_pthread_save_ac_link="$ac_link"
+             ax_pthread_sed='s/conftest\.\$ac_ext/conftest.$ac_objext/g'
+             ax_pthread_link_step=`$as_echo "$ac_link" | sed "$ax_pthread_sed"`
+             ax_pthread_2step_ac_link="($ac_compile) && (echo ==== >&5) && ($ax_pthread_link_step)"
+             ax_pthread_save_CFLAGS="$CFLAGS"
+             for ax_pthread_try in '' -Qunused-arguments -Wno-unused-command-line-argument unknown; do
+                AS_IF([test "x$ax_pthread_try" = "xunknown"], [break])
+                CFLAGS="-Werror -Wunknown-warning-option $ax_pthread_try -pthread $ax_pthread_save_CFLAGS"
+                ac_link="$ax_pthread_save_ac_link"
+                AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],
+                    [ac_link="$ax_pthread_2step_ac_link"
+                     AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void){return 0;}]])],
+                         [break])
+                    ])
+             done
+             ac_link="$ax_pthread_save_ac_link"
+             CFLAGS="$ax_pthread_save_CFLAGS"
+             AS_IF([test "x$ax_pthread_try" = "x"], [ax_pthread_try=no])
+             ax_cv_PTHREAD_CLANG_NO_WARN_FLAG="$ax_pthread_try"
+            ])
+
+        case "$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG" in
+                no | unknown) ;;
+                *) PTHREAD_CFLAGS="$ax_cv_PTHREAD_CLANG_NO_WARN_FLAG $PTHREAD_CFLAGS" ;;
+        esac
+
+fi # $ax_pthread_clang = yes
+
+if test "x$ax_pthread_ok" = "xno"; then
+for ax_pthread_try_flag in $ax_pthread_flags; do
+
+        case $ax_pthread_try_flag in
+                none)
+                AC_MSG_CHECKING([whether pthreads work without any flags])
+                ;;
+
+                -mt,pthread)
+                AC_MSG_CHECKING([whether pthreads work with -mt -lpthread])
+                PTHREAD_CFLAGS="-mt"
+                PTHREAD_LIBS="-lpthread"
+                ;;
+
+                -*)
+                AC_MSG_CHECKING([whether pthreads work with $ax_pthread_try_flag])
+                PTHREAD_CFLAGS="$ax_pthread_try_flag"
+                ;;
+
+                pthread-config)
+                AC_CHECK_PROG([ax_pthread_config], [pthread-config], [yes], [no])
+                AS_IF([test "x$ax_pthread_config" = "xno"], [continue])
+                PTHREAD_CFLAGS="`pthread-config --cflags`"
+                PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
+                ;;
+
+                *)
+                AC_MSG_CHECKING([for the pthreads library -l$ax_pthread_try_flag])
+                PTHREAD_LIBS="-l$ax_pthread_try_flag"
+                ;;
+        esac
+
+        ax_pthread_save_CFLAGS="$CFLAGS"
+        ax_pthread_save_LIBS="$LIBS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+
+        # Check for various functions.  We must include pthread.h,
+        # since some functions may be macros.  (On the Sequent, we
+        # need a special flag -Kthread to make this header compile.)
+        # We check for pthread_join because it is in -lpthread on IRIX
+        # while pthread_create is in libc.  We check for pthread_attr_init
+        # due to DEC craziness with -lpthreads.  We check for
+        # pthread_cleanup_push because it is one of the few pthread
+        # functions on Solaris that doesn't have a non-functional libc stub.
+        # We try pthread_create on general principles.
+
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>
+#                       if $ax_pthread_check_cond
+#                        error "$ax_pthread_check_macro must be defined"
+#                       endif
+                        static void routine(void *a) { a = 0; }
+                        static void *start_routine(void *a) { return a; }],
+                       [pthread_t th; pthread_attr_t attr;
+                        pthread_create(&th, 0, start_routine, 0);
+                        pthread_join(th, 0);
+                        pthread_attr_init(&attr);
+                        pthread_cleanup_push(routine, 0);
+                        pthread_cleanup_pop(0) /* ; */])],
+            [ax_pthread_ok=yes],
+            [])
+
+        CFLAGS="$ax_pthread_save_CFLAGS"
+        LIBS="$ax_pthread_save_LIBS"
+
+        AC_MSG_RESULT([$ax_pthread_ok])
+        AS_IF([test "x$ax_pthread_ok" = "xyes"], [break])
+
+        PTHREAD_LIBS=""
+        PTHREAD_CFLAGS=""
+done
+fi
+
+# Various other checks:
+if test "x$ax_pthread_ok" = "xyes"; then
+        ax_pthread_save_CFLAGS="$CFLAGS"
+        ax_pthread_save_LIBS="$LIBS"
+        CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+        LIBS="$PTHREAD_LIBS $LIBS"
+
+        # Detect AIX lossage: JOINABLE attribute is called UNDETACHED.
+        AC_CACHE_CHECK([for joinable pthread attribute],
+            [ax_cv_PTHREAD_JOINABLE_ATTR],
+            [ax_cv_PTHREAD_JOINABLE_ATTR=unknown
+             for ax_pthread_attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do
+                 AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <pthread.h>],
+                                                 [int attr = $ax_pthread_attr; return attr /* ; */])],
+                                [ax_cv_PTHREAD_JOINABLE_ATTR=$ax_pthread_attr; break],
+                                [])
+             done
+            ])
+        AS_IF([test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xunknown" && \
+               test "x$ax_cv_PTHREAD_JOINABLE_ATTR" != "xPTHREAD_CREATE_JOINABLE" && \
+               test "x$ax_pthread_joinable_attr_defined" != "xyes"],
+              [AC_DEFINE_UNQUOTED([PTHREAD_CREATE_JOINABLE],
+                                  [$ax_cv_PTHREAD_JOINABLE_ATTR],
+                                  [Define to necessary symbol if this constant
+                                   uses a non-standard name on your system.])
+               ax_pthread_joinable_attr_defined=yes
+              ])
+
+        AC_CACHE_CHECK([whether more special flags are required for pthreads],
+            [ax_cv_PTHREAD_SPECIAL_FLAGS],
+            [ax_cv_PTHREAD_SPECIAL_FLAGS=no
+             case $host_os in
+             solaris*)
+             ax_cv_PTHREAD_SPECIAL_FLAGS="-D_POSIX_PTHREAD_SEMANTICS"
+             ;;
+             esac
+            ])
+        AS_IF([test "x$ax_cv_PTHREAD_SPECIAL_FLAGS" != "xno" && \
+               test "x$ax_pthread_special_flags_added" != "xyes"],
+              [PTHREAD_CFLAGS="$ax_cv_PTHREAD_SPECIAL_FLAGS $PTHREAD_CFLAGS"
+               ax_pthread_special_flags_added=yes])
+
+        AC_CACHE_CHECK([for PTHREAD_PRIO_INHERIT],
+            [ax_cv_PTHREAD_PRIO_INHERIT],
+            [AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <pthread.h>]],
+                                             [[int i = PTHREAD_PRIO_INHERIT;]])],
+                            [ax_cv_PTHREAD_PRIO_INHERIT=yes],
+                            [ax_cv_PTHREAD_PRIO_INHERIT=no])
+            ])
+        AS_IF([test "x$ax_cv_PTHREAD_PRIO_INHERIT" = "xyes" && \
+               test "x$ax_pthread_prio_inherit_defined" != "xyes"],
+              [AC_DEFINE([HAVE_PTHREAD_PRIO_INHERIT], [1], [Have PTHREAD_PRIO_INHERIT.])
+               ax_pthread_prio_inherit_defined=yes
+              ])
+
+        CFLAGS="$ax_pthread_save_CFLAGS"
+        LIBS="$ax_pthread_save_LIBS"
+
+        # More AIX lossage: compile with *_r variant
+        if test "x$GCC" != "xyes"; then
+            case $host_os in
+                aix*)
+                AS_CASE(["x/$CC"],
+                    [x*/c89|x*/c89_128|x*/c99|x*/c99_128|x*/cc|x*/cc128|x*/xlc|x*/xlc_v6|x*/xlc128|x*/xlc128_v6],
+                    [#handle absolute path differently from PATH based program lookup
+                     AS_CASE(["x$CC"],
+                         [x/*],
+                         [AS_IF([AS_EXECUTABLE_P([${CC}_r])],[PTHREAD_CC="${CC}_r"])],
+                         [AC_CHECK_PROGS([PTHREAD_CC],[${CC}_r],[$CC])])])
+                ;;
+            esac
+        fi
+fi
+
+test -n "$PTHREAD_CC" || PTHREAD_CC="$CC"
+
+AC_SUBST([PTHREAD_LIBS])
+AC_SUBST([PTHREAD_CFLAGS])
+AC_SUBST([PTHREAD_CC])
+
+# Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
+if test "x$ax_pthread_ok" = "xyes"; then
+        ifelse([$1],,[AC_DEFINE([HAVE_PTHREAD],[1],[Define if you have POSIX threads libraries and header files.])],[$1])
+        :
+else
+        ax_pthread_ok=no
+        $2
+fi
+AC_LANG_POP
+])dnl AX_PTHREAD
diff --git a/gold/Makefile.am b/gold/Makefile.am
index 675deecb47..f87067aab4 100644
--- a/gold/Makefile.am
+++ b/gold/Makefile.am
@@ -31,8 +31,11 @@  ACLOCAL_AMFLAGS = -I ../bfd -I ../config
 ZLIB = @zlibdir@ -lz
 ZLIBINC = @zlibinc@
 
-AM_CFLAGS = $(WARN_CFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC)
-AM_CXXFLAGS = $(WARN_CXXFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC)
+THREADFLAGS = @PTHREAD_CFLAGS@
+THREADLIBS = @PTHREAD_LIBS@
+
+AM_CFLAGS = $(WARN_CFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC) $(THREADFLAGS)
+AM_CXXFLAGS = $(WARN_CXXFLAGS) $(LFS_CFLAGS) $(RANDOM_SEED_CFLAGS) $(ZLIBINC) $(THREADFLAGS)
 
 AM_CPPFLAGS = \
 	-I$(srcdir) -I$(srcdir)/../include -I$(srcdir)/../elfcpp \
@@ -46,10 +49,6 @@  if PLUGINS
 LIBDL = @DLOPEN_LIBS@
 endif
 
-if THREADS
-THREADSLIB = -lpthread
-endif
-
 AM_YFLAGS = -d
 
 # Automake 1.10+ disables lex and yacc output file regeneration if
diff --git a/gold/aclocal.m4 b/gold/aclocal.m4
index 47cb21fc5a..2f34365173 100644
--- a/gold/aclocal.m4
+++ b/gold/aclocal.m4
@@ -1000,6 +1000,7 @@  AC_SUBST([am__tar])
 AC_SUBST([am__untar])
 ]) # _AM_PROG_TAR
 
+m4_include([../config/ax_pthread.m4])
 m4_include([../config/depstand.m4])
 m4_include([../config/gettext-sister.m4])
 m4_include([../config/lcmessage.m4])
diff --git a/gold/configure.ac b/gold/configure.ac
index 5ba43f2f95..bd21335a17 100644
--- a/gold/configure.ac
+++ b/gold/configure.ac
@@ -85,21 +85,6 @@  AC_ARG_ENABLE(gold,
 AC_SUBST(install_as_default)
 AC_SUBST(installed_linker)
 
-dnl For now threads are a configure time option.
-AC_ARG_ENABLE([threads],
-[  --enable-threads        multi-threaded linking],
-[case "${enableval}" in
-  yes | "") threads=yes ;;
-  no) threads=no ;;
-  *) threads=yes ;;
- esac],
-[threads=no])
-if test "$threads" = "yes"; then
-  AC_DEFINE(ENABLE_THREADS, 1,
-	    [Define to do multi-threaded linking])
-fi
-AM_CONDITIONAL(THREADS, test "$threads" = "yes")
-
 AC_ARG_ENABLE([plugins],
 [  --enable-plugins        linker plugins],
 [case "${enableval}" in
@@ -570,6 +555,29 @@  fi
 # Link in zlib if we can.  This allows us to write compressed sections.
 AM_ZLIB
 
+
+AC_ARG_ENABLE([threads],
+[[  --enable-threads[=ARG]  multi-threaded linking [ARG={auto,yes,no}]]],
+[case "${enableval}" in
+  yes | "") threads=yes ;;
+  no) threads=no ;;
+  auto) threads=auto ;;
+  *) threads=yes ;;
+ esac],
+[threads=auto])
+
+if test "$threads" = "yes"; then
+  AX_PTHREAD([thread=yes], AC_MSG_ERROR([pthread not found]))
+elif test "$threads" = "auto"; then
+  AX_PTHREAD([threads=yes], [threads=no])
+fi
+
+if test "$threads" = "yes"; then
+  AC_DEFINE(ENABLE_THREADS, 1,
+	    [Define to do multi-threaded linking])
+fi
+AM_CONDITIONAL(THREADS, test "$threads" = "yes")
+
 dnl We have to check these in C, not C++, because autoconf generates
 dnl tests which have no type information, and current glibc provides
 dnl multiple declarations of functions like basename when compiling