From ab1bfc33c87726dc1fd85c351191380c6c463143 Mon Sep 17 00:00:00 2001
From: Ivan Maidanski <ivmai@mail.ru>
Date: Thu, 18 Aug 2022 00:31:05 +0300
Subject: Link with rt library to get clock_gettime where necessary

Issue #450 (bdwgc).

This patch adds the logic to CMake and configure scripts to pass -lrt
option during linking to avoid unresolved clock_gettime on some hosts.

* CMakeLists.txt [!NEED_LIB_RT] (HAVE_CLOCK_GETTIME_DIRECTLY): Set
variable by check_function_exists(clock_gettime).
* CMakeLists.txt [!NEED_LIB_RT && !HAVE_CLOCK_GETTIME_DIRECTLY]
(NEED_LIB_RT): Set to ON.
* CMakeLists.txt (LIBRT): Refine comment.
* CMakeLists.txt (gc): Specify target_link_libraries regardless of
enable_threads.
* Makefile.am (libgc_la_LIBADD): Update comment.
* configure.ac (need_lib_rt): Define variable (and set to false).
* configure.ac [$THREADS==pthreads && ($host==*-*-hpux11*
|| $host==*-*-netbsd* || $host== *-*-solaris* || $host==*-*-osf*)]
(THREADDLLIBS): Do not add "-lrt" directly.
* configure.ac [$THREADS==pthreads && ($host==*-*-hpux11*
|| $host==*-*-netbsd* || $host== *-*-solaris* || $host==*-*-osf*)]
(need_lib_rt): Set to true.
* configure.ac [!need_lib_rt && !AC_LINK_IFELSE(clock_gettime)
&& AC_CHECK_LIB(rt,clock_gettime)] (need_lib_rt): Set to true.
* configure.ac [need_lib_rt] (THREADDLLIBS): Append "-lrt".
---
 configure.ac | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

(limited to 'configure.ac')

diff --git a/configure.ac b/configure.ac
index 2a9e3898..1293b037 100644
--- a/configure.ac
+++ b/configure.ac
@@ -190,6 +190,7 @@ CFLAGS="$old_CFLAGS"
 
 THREADDLLIBS=
 need_atomic_ops_asm=false
+need_lib_rt=false
 compile_asm=false
 use_parallel_mark=no
 use_thread_local_alloc=no
@@ -221,8 +222,9 @@ case "$THREADS" in
       *-*-hpux11*)
         AC_MSG_WARN("Only HP/UX 11 POSIX threads are supported.")
         AC_DEFINE(_POSIX_C_SOURCE,199506L)
-        THREADDLLIBS="-lpthread -lrt"
+        THREADDLLIBS="-lpthread"
         # HPUX needs REENTRANT for the _r calls.
+        need_lib_rt=true
         ;;
       *-*-openbsd*)
         AM_CFLAGS="$AM_CFLAGS -pthread"
@@ -241,10 +243,12 @@ case "$THREADS" in
       *-*-netbsd*)
         AC_MSG_WARN("Only on NetBSD 2.0 or later.")
         AC_DEFINE(_PTHREADS)
-        THREADDLLIBS="-lpthread -lrt"
+        THREADDLLIBS="-lpthread"
+        need_lib_rt=true
         ;;
       *-*-solaris*)
-        THREADDLLIBS="-lpthread -lrt"
+        THREADDLLIBS="-lpthread"
+        need_lib_rt=true
         ;;
       *-*-cygwin* | *-*-msys*)
         # Cygwin doesn't have a real libpthread, so Libtool can't link
@@ -265,7 +269,8 @@ case "$THREADS" in
         ;;
       *-*-osf*)
         AM_CFLAGS="$AM_CFLAGS -pthread"
-        THREADDLLIBS="-lpthread -lrt"
+        THREADDLLIBS="-lpthread"
+        need_lib_rt=true
         ;;
       *)
         AS_IF([test x$default_threadlibs != xtrue],
@@ -328,7 +333,22 @@ case "$THREADS" in
     AC_MSG_ERROR($THREADS is an unknown thread package)
     ;;
 esac
+
+# Check whether -lrt linker option is needed to use clock_gettime.
+if test "x$need_lib_rt" != xtrue; then
+  AC_MSG_CHECKING(for clock_gettime without additional libraries)
+  AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <time.h>],
+                    [struct timespec t; clock_gettime(CLOCK_REALTIME, &t)])],
+    [AC_MSG_RESULT(yes)],
+    [AC_MSG_RESULT(no)
+     AC_CHECK_LIB(rt, clock_gettime, [need_lib_rt=true])])
+fi
+
+if test "x$need_lib_rt" = xtrue; then
+  THREADDLLIBS="$THREADDLLIBS -lrt"
+fi
 AC_SUBST(THREADDLLIBS)
+
 AM_CONDITIONAL(THREADS, test x$THREADS != xnone)
 AM_CONDITIONAL(PTHREADS, test x$THREADS = xposix)
 AM_CONDITIONAL(DARWIN_THREADS, test x$darwin_threads = xtrue)
-- 
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