Remove configure probe for dlopen, and refactor.

dlopen() is in SUSv2 and all targeted Unix systems have it.  We still
need replacement functions for Windows, but we don't need a configure
probe for that.

Since it's no longer needed by other operating systems, rename dlopen.c
to win32dlopen.c and move the declarations into win32_port.h.

Likewise, the macros RTLD_NOW and RTLD_GLOBAL now only need to be
defined on Windows, since all targeted Unix systems have 'em.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA+hUKGJ3LHeP9w5Fgzdr4G8AnEtJ=z=p6hGDEm4qYGEUX5B6fQ@mail.gmail.com

src/backend/utils/fmgr/dfmgr.c

@@ -16,7 +16,7 @@
 
 #include <sys/stat.h>
 
-#ifdef HAVE_DLOPEN
+#ifndef WIN32
 #include <dlfcn.h>
 
 /*
@@ -28,7 +28,7 @@
 #undef bool
 #endif
 #endif
-#endif							/* HAVE_DLOPEN */
+#endif							/* !WIN32 */
 
 #include "fmgr.h"
 #include "lib/stringinfo.h"

src/include/pg_config.h.in

@@ -141,14 +141,6 @@
    don't. */
 #undef HAVE_DECL_PWRITEV
 
-/* Define to 1 if you have the declaration of `RTLD_GLOBAL', and to 0 if you
-   don't. */
-#undef HAVE_DECL_RTLD_GLOBAL
-
-/* Define to 1 if you have the declaration of `RTLD_NOW', and to 0 if you
-   don't. */
-#undef HAVE_DECL_RTLD_NOW
-
 /* Define to 1 if you have the declaration of `strlcat', and to 0 if you
    don't. */
 #undef HAVE_DECL_STRLCAT
@@ -169,9 +161,6 @@
    don't. */
 #undef HAVE_DECL_STRTOULL
 
-/* Define to 1 if you have the `dlopen' function. */
-#undef HAVE_DLOPEN
-
 /* Define to 1 if you have the <editline/history.h> header file. */
 #undef HAVE_EDITLINE_HISTORY_H
 

src/include/port.h

@@ -455,29 +455,6 @@ extern int	setenv(const char *name, const char *value, int overwrite);
 extern int	unsetenv(const char *name);
 #endif
 
-#ifndef HAVE_DLOPEN
-extern void *dlopen(const char *file, int mode);
-extern void *dlsym(void *handle, const char *symbol);
-extern int	dlclose(void *handle);
-extern char *dlerror(void);
-#endif
-
-/*
- * In some older systems, the RTLD_NOW flag isn't defined and the mode
- * argument to dlopen must always be 1.
- */
-#if !HAVE_DECL_RTLD_NOW
-#define RTLD_NOW 1
-#endif
-
-/*
- * The RTLD_GLOBAL flag is wanted if available, but it doesn't exist
- * everywhere.  If it doesn't exist, set it to 0 so it has no effect.
- */
-#if !HAVE_DECL_RTLD_GLOBAL
-#define RTLD_GLOBAL 0
-#endif
-
 /* thread.c */
 #ifndef WIN32
 extern bool pg_get_user_name(uid_t user_id, char *buffer, size_t buflen);

src/include/port/win32_port.h

@@ -503,6 +503,15 @@ extern int	pgwin32_ReserveSharedMemoryRegion(HANDLE);
 /* in backend/port/win32/crashdump.c */
 extern void pgwin32_install_crashdump_handler(void);
 
+/* in port/win32dlopen.c */
+extern void *dlopen(const char *file, int mode);
+extern void *dlsym(void *handle, const char *symbol);
+extern int	dlclose(void *handle);
+extern char *dlerror(void);
+
+#define RTLD_NOW 1
+#define RTLD_GLOBAL 0
+
 /* in port/win32error.c */
 extern void _dosmaperr(unsigned long);
 

src/port/win32dlopen.c

@@ -1,22 +1,20 @@
 /*-------------------------------------------------------------------------
  *
- * dlopen.c
- *	  dynamic loader for platforms without dlopen()
+ * win32dlopen.c
+ *	  dynamic loader for Windows
  *
  * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *
  * IDENTIFICATION
- *	  src/port/dlopen.c
+ *	  src/port/win32dlopen.c
  *
  *-------------------------------------------------------------------------
  */
 
 #include "c.h"
 
-#if defined(WIN32)
-
 static char last_dyn_error[512];
 
 static void
@@ -93,5 +91,3 @@ dlopen(const char *file, int mode)
 	last_dyn_error[0] = 0;
 	return (void *) h;
 }
-
-#endif

src/tools/msvc/Mkvcbuild.pm

@@ -103,11 +103,12 @@ sub mkvcbuild
 	  getpeereid.c getrusage.c inet_aton.c
 	  getaddrinfo.c gettimeofday.c inet_net_ntop.c kill.c open.c
 	  snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c
-	  dirent.c dlopen.c getopt.c getopt_long.c link.c
+	  dirent.c getopt.c getopt_long.c link.c
 	  pread.c preadv.c pwrite.c pwritev.c pg_bitutils.c
 	  pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c
 	  pqsignal.c mkdtemp.c qsort.c qsort_arg.c bsearch_arg.c quotes.c system.c
 	  strerror.c tar.c
+	  win32dlopen.c
 	  win32env.c win32error.c win32ntdll.c
 	  win32security.c win32setlocale.c win32stat.c);
 

src/tools/msvc/Solution.pm

@@ -244,14 +244,11 @@ sub GenerateFiles
 		HAVE_DECL_POSIX_FADVISE                     => 0,
 		HAVE_DECL_PREADV                            => 0,
 		HAVE_DECL_PWRITEV                           => 0,
-		HAVE_DECL_RTLD_GLOBAL                       => 0,
-		HAVE_DECL_RTLD_NOW                          => 0,
 		HAVE_DECL_STRLCAT                           => 0,
 		HAVE_DECL_STRLCPY                           => 0,
 		HAVE_DECL_STRNLEN                           => 1,
 		HAVE_DECL_STRTOLL                           => 1,
 		HAVE_DECL_STRTOULL                          => 1,
-		HAVE_DLOPEN                                 => undef,
 		HAVE_EDITLINE_HISTORY_H                     => undef,
 		HAVE_EDITLINE_READLINE_H                    => undef,
 		HAVE_EXECINFO_H                             => undef,