Re: new module 'setlocale-null'

[Bruno Haible]

This patch ensures that the gl_get_setlocale_null_lock function gets
exported from shared libraries (such as libintl.so) also on ELF systems,
so that different shared libraries attached to the same process use the
same lock.


2019-12-23  Bruno Haible  <br...@clisp.org>

        setlocale-null: Export the lock function also on non-Windows platforms.
        * lib/setlocale-lock.c (DLL_EXPORTED): New macro.
        (gl_get_setlocale_null_lock): Declare as DLL_EXPORTED.
        * m4/setlocale_null.m4 (gl_PREREQ_SETLOCALE_LOCK): New macro.
        * modules/setlocale-null (configure.ac): Invoke it.
        (Files): Add m4/visibility.m4.

diff --git a/lib/setlocale-lock.c b/lib/setlocale-lock.c
index 9c47afc..60c1ba3 100644
--- a/lib/setlocale-lock.c
+++ b/lib/setlocale-lock.c
@@ -25,6 +25,19 @@
 /* Prohibit renaming this symbol.  */
 #undef gl_get_setlocale_null_lock
 
+/* Macro for exporting a symbol (function, not variable) defined in this file,
+   when compiled into a shared library.  */
+#ifndef DLL_EXPORTED
+# if HAVE_VISIBILITY
+  /* Override the effect of the compiler option '-fvisibility=hidden'.  */
+#  define DLL_EXPORTED __attribute__((__visibility__("default")))
+# elif defined _WIN32 || defined __CYGWIN__
+#  define DLL_EXPORTED __declspec(dllexport)
+# else
+#  define DLL_EXPORTED
+# endif
+#endif
+
 #if defined _WIN32 && !defined __CYGWIN__
 
 # define WIN32_LEAN_AND_MEAN  /* avoid including junk */
@@ -36,7 +49,7 @@
    because the latter is not guaranteed to be a stable ABI in the future.  */
 
 /* Make sure the function gets exported from DLLs.  */
-__declspec(dllexport) CRITICAL_SECTION *gl_get_setlocale_null_lock (void);
+DLL_EXPORTED CRITICAL_SECTION *gl_get_setlocale_null_lock (void);
 
 static glwthread_initguard_t guard = GLWTHREAD_INITGUARD_INIT;
 static CRITICAL_SECTION lock;
@@ -72,10 +85,8 @@ gl_get_setlocale_null_lock (void)
 
 static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
 
-# if defined _WIN32 || defined __CYGWIN__
-/* Make sure the function gets exported from DLLs.  */
-__declspec(dllexport) pthread_mutex_t *gl_get_setlocale_null_lock (void);
-# endif
+/* Make sure the function gets exported from shared libraries.  */
+DLL_EXPORTED pthread_mutex_t *gl_get_setlocale_null_lock (void);
 
 /* Returns the internal lock used by setlocale_null_r.  */
 pthread_mutex_t *
@@ -101,6 +112,9 @@ atomic_init (void)
   init_needed = 0;
 }
 
+/* Make sure the function gets exported from shared libraries.  */
+DLL_EXPORTED mtx_t *gl_get_setlocale_null_lock (void);
+
 /* Returns the internal lock used by setlocale_null_r.  */
 mtx_t *
 gl_get_setlocale_null_lock (void)
diff --git a/m4/setlocale_null.m4 b/m4/setlocale_null.m4
index eff6e76..465ef11 100644
--- a/m4/setlocale_null.m4
+++ b/m4/setlocale_null.m4
@@ -90,3 +90,9 @@ AC_DEFUN([gl_FUNC_SETLOCALE_NULL],
   dnl with gcc or xlc, and empty otherwise.
   AC_SUBST([LIB_SETLOCALE_NULL])
 ])
+
+# Prerequisites of lib/setlocale-lock.c.
+AC_DEFUN([gl_PREREQ_SETLOCALE_LOCK],
+[
+  gl_VISIBILITY
+])
diff --git a/modules/setlocale-null b/modules/setlocale-null
index 5240369..2774004 100644
--- a/modules/setlocale-null
+++ b/modules/setlocale-null
@@ -8,6 +8,7 @@ lib/setlocale-lock.c
 lib/windows-initguard.h
 m4/setlocale_null.m4
 m4/threadlib.m4
+m4/visibility.m4
 
 Depends-on:
 locale
@@ -17,6 +18,7 @@ configure.ac:
 gl_FUNC_SETLOCALE_NULL
 if test $SETLOCALE_NULL_ALL_MTSAFE = 0 || test $SETLOCALE_NULL_ONE_MTSAFE = 0; 
then
   AC_LIBOBJ([setlocale-lock])
+  gl_PREREQ_SETLOCALE_LOCK
 fi
 gl_LOCALE_MODULE_INDICATOR([setlocale_null])