From 677b0c03f8fca937f6b16da3341602637d092179 Mon Sep 17 00:00:00 2001
From: Nikias Bassen
Date: Mon, 13 Sep 2021 18:41:59 +0200
Subject: Check availability of constructor attribute and use it on Windows in
 favor of DllMain

---
 configure.ac | 26 ++++++++++++++++++++++----
 src/plist.c  | 39 +++++++++++++++++++++++----------------
 2 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/configure.ac b/configure.ac
index 9300f31..0d13e04 100644
--- a/configure.ac
+++ b/configure.ac
@@ -55,17 +55,17 @@ AC_C_BIGENDIAN([AC_DEFINE([__BIG_ENDIAN__], [1], [big endian])],
 
 
 # Check for operating system
-AC_MSG_CHECKING([wether we need platform-specific build settings for ${host_os}])
+AC_MSG_CHECKING([for platform-specific build settings])
 case ${host_os} in
   *mingw32*|*cygwin*)
-    AC_MSG_RESULT([yes])
+    AC_MSG_RESULT([${host_os}])
     win32=true
     ;;
   darwin*|*android*)
-    AC_MSG_RESULT([no])
+    AC_MSG_RESULT([${host_os}])
     ;;
   *)
-    AC_MSG_RESULT([yes])
+    AC_MSG_RESULT([${host_os}])
     AX_PTHREAD([], [AC_MSG_ERROR([pthread is required to build libplist])])
     AC_CHECK_LIB(pthread, [pthread_once], [], [AC_MSG_ERROR([pthread with pthread_once required to build libplist])])
     ;;
@@ -74,6 +74,24 @@ AM_CONDITIONAL(WIN32, test x$win32 = xtrue)
 
 AC_SEARCH_LIBS([fmin],[m])
 
+# Check if the C compiler supports __attribute__((constructor))
+AC_CACHE_CHECK([wether the C compiler supports constructor/destructor attributes],
+  ac_cv_attribute_constructor, [
+  ac_cv_attribute_constructor=no
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+    [[
+      static void __attribute__((constructor)) test_constructor(void) {
+      }
+      static void __attribute__((destructor)) test_destructor(void) {
+      }
+    ]], [])],
+    [ac_cv_attribute_constructor=yes]
+  )]
+)
+if test "$ac_cv_attribute_constructor" = "yes"; then
+  AC_DEFINE(HAVE_ATTRIBUTE_CONSTRUCTOR, 1, [Define if the C compiler supports constructor/destructor attributes])
+fi
+
 # Check if struct tm has a tm_gmtoff member
 AC_CACHE_CHECK(for tm_gmtoff in struct tm, ac_cv_struct_tm_gmtoff,
   AC_COMPILE_IFELSE([AC_LANG_PROGRAM([
diff --git a/src/plist.c b/src/plist.c
index 454d08c..d0e6c77 100644
--- a/src/plist.c
+++ b/src/plist.c
@@ -63,7 +63,6 @@ static void internal_plist_deinit(void)
 }
 
 #ifdef WIN32
-
 typedef volatile struct {
     LONG lock;
     int state;
@@ -83,7 +82,29 @@ static void thread_once(thread_once_t *once_control, void (*init_routine)(void))
     }
     InterlockedExchange(&(once_control->lock), 0);
 }
+#else
+static pthread_once_t init_once = PTHREAD_ONCE_INIT;
+static pthread_once_t deinit_once = PTHREAD_ONCE_INIT;
+#define thread_once pthread_once
+#endif
+
+#ifndef HAVE_ATTRIBUTE_CONSTRUCTOR
+  #if defined(__llvm__) || defined(__GNUC__)
+    #define HAVE_ATTRIBUTE_CONSTRUCTOR
+  #endif
+#endif
+
+#ifdef HAVE_ATTRIBUTE_CONSTRUCTOR
+static void __attribute__((constructor)) libplist_initialize(void)
+{
+    thread_once(&init_once, internal_plist_init);
+}
 
+static void __attribute__((destructor)) libplist_deinitialize(void)
+{
+    thread_once(&deinit_once, internal_plist_deinit);
+}
+#elif defined(WIN32)
 BOOL WINAPI DllMain(HINSTANCE hModule, DWORD dwReason, LPVOID lpReserved)
 {
     switch (dwReason) {
@@ -98,22 +119,8 @@ BOOL WINAPI DllMain(HINSTANCE hModule, DWORD dwReason, LPVOID lpReserved)
     }
     return 1;
 }
-
 #else
-
-static pthread_once_t init_once = PTHREAD_ONCE_INIT;
-static pthread_once_t deinit_once = PTHREAD_ONCE_INIT;
-
-static void __attribute__((constructor)) libplist_initialize(void)
-{
-    pthread_once(&init_once, internal_plist_init);
-}
-
-static void __attribute__((destructor)) libplist_deinitialize(void)
-{
-    pthread_once(&deinit_once, internal_plist_deinit);
-}
-
+#warning No compiler support for constructor/destructor attributes, some features might not be available.
 #endif
 
 #ifndef HAVE_MEMMEM
-- 
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