Build: Update m4/ax_pthread.m4 from Autoconf Archive (again).

m4/ax_pthread.m4

@@ -55,6 +55,7 @@
 #
 #   Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
 #   Copyright (c) 2011 Daniel Richard G. <skunk@iSKUNK.ORG>
+#   Copyright (c) 2019 Marc Stevens <marc.stevens@cwi.nl>
 #
 #   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
@@ -82,7 +83,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 26
+#serial 27
 
 AU_ALIAS([ACX_PTHREAD], [AX_PTHREAD])
 AC_DEFUN([AX_PTHREAD], [
@@ -123,10 +124,12 @@ fi
 # (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
+# Create a list of thread flags to try. Items with a "," contain both
-# C compiler flags, and other items are library names, except for "none"
+# C compiler flags (before ",") and linker flags (after ","). Other items
-# which indicates that we try without any flags at all, and "pthread-config"
+# starting with a "-" are C compiler flags, and remaining items are
-# which is a program returning the flags for the Pth emulation library.
+# 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"
 
@@ -194,14 +197,47 @@ case $host_os in
         # 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"
+        ax_pthread_flags="-mt,-lpthread pthread $ax_pthread_flags"
         ;;
 esac
 
+# 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"
+
+
 # GCC generally uses -pthread, or -pthreads on some platforms (e.g. SPARC)
 
+# Note that for GCC and Clang -pthread generally implies -lpthread,
+# except when -nostdlib is passed.
+# This is problematic using libtool to build C++ shared libraries with pthread:
+# [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25460
+# [2] https://bugzilla.redhat.com/show_bug.cgi?id=661333
+# [3] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=468555
+# To solve this, first try -pthread together with -lpthread for GCC
+
 AS_IF([test "x$GCC" = "xyes"],
-      [ax_pthread_flags="-pthread -pthreads $ax_pthread_flags"])
+      [ax_pthread_flags="-pthread,-lpthread -pthread -pthreads $ax_pthread_flags"])
+
+# Clang takes -pthread (never supported any other flag), but we'll try with -lpthread first
+
+AS_IF([test "x$ax_pthread_clang" = "xyes"],
+      [ax_pthread_flags="-pthread,-lpthread -pthread"])
+
 
 # The presence of a feature test macro requesting re-entrant function
 # definitions is, on some systems, a strong hint that pthreads support is
@@ -224,101 +260,6 @@ 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
@@ -328,10 +269,10 @@ for ax_pthread_try_flag in $ax_pthread_flags; do
                 AC_MSG_CHECKING([whether pthreads work without any flags])
                 ;;
 
-                -mt,pthread)
+                *,*)
-                AC_MSG_CHECKING([whether pthreads work with -mt -lpthread])
+                PTHREAD_CFLAGS=`echo $ax_pthread_try_flag | sed "s/^\(.*\),\(.*\)$/\1/"`
-                PTHREAD_CFLAGS="-mt"
+                PTHREAD_LIBS=`echo $ax_pthread_try_flag | sed "s/^\(.*\),\(.*\)$/\2/"`
-                PTHREAD_LIBS="-lpthread"
+                AC_MSG_CHECKING([whether pthreads work with "$PTHREAD_CFLAGS" and "$PTHREAD_LIBS"])
                 ;;
 
                 -*)
@@ -399,6 +340,80 @@ for ax_pthread_try_flag in $ax_pthread_flags; do
 done
 fi
 
+
+# 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.)
+
+        # 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 # $ax_pthread_clang = yes
+
+
+
 # Various other checks:
 if test "x$ax_pthread_ok" = "xyes"; then
         ax_pthread_save_CFLAGS="$CFLAGS"