From 3ca5357bbdb9aae29a1785d5ca2179d6cca15cdd Mon Sep 17 00:00:00 2001
From: Wolfgang Walther <walther@technowledgy.de>
Date: Sun, 2 Jun 2024 10:46:56 +0200
Subject: [PATCH v2] Make building with clang's LTO work on macOS

When building with -flto the backend binary must keep many otherwise
unused symbols to make them available to dynamically loaded modules /
extensions.  This has been done via -Wl,--export-dynamic on many
platforms for years.  This flag is not supported by Apple's clang,
though.  Here it's called -Wl,-export_dynamic instead.

Thus, make configure pick up on this variant of the flag as well.  Meson
has the logic to detect this flag built-in, but doesn't support this
variant either.  This needs to be raised upstream.

Without this fix, building with -flto fails with errors similar to [1]
and [2].  This happens for all currently live versions, including 17 and
HEAD.

[1]: https://postgr.es/m/1581936537572-0.post%40n3.nabble.com
[2]: https://postgr.es/m/21800.1499270547%40sss.pgh.pa.us
---
 configure    | 41 +++++++++++++++++++++++++++++++++++++++++
 configure.ac |  4 ++++
 2 files changed, 45 insertions(+)

diff --git a/configure b/configure
index 7b03db56a67..771dcfbdef9 100755
--- a/configure
+++ b/configure
@@ -19135,6 +19135,7 @@ fi
 # For linkers that understand --export-dynamic, add that to the LDFLAGS_EX_BE
 # (backend specific ldflags). One some platforms this will always fail (e.g.,
 # windows), but on others it depends on the choice of linker (e.g., solaris).
+# macos uses -export_dynamic instead.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -Wl,--export-dynamic, for LDFLAGS_EX_BE" >&5
 $as_echo_n "checking whether $CC supports -Wl,--export-dynamic, for LDFLAGS_EX_BE... " >&6; }
 if ${pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl___export_dynamic+:} false; then :
@@ -19173,6 +19174,46 @@ if test x"$pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl___export_dynamic" = x"yes"; then
   LDFLAGS_EX_BE="${LDFLAGS_EX_BE} -Wl,--export-dynamic"
 fi
 
+if test x"$LDFLAGS_EX_BE" = x""; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -Wl,-export_dynamic, for LDFLAGS_EX_BE" >&5
+$as_echo_n "checking whether $CC supports -Wl,-export_dynamic, for LDFLAGS_EX_BE... " >&6; }
+if ${pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl__export_dynamic+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_LDFLAGS=$LDFLAGS
+LDFLAGS="$pgac_save_LDFLAGS -Wl,-export_dynamic"
+if test "$cross_compiling" = yes; then :
+  pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl__export_dynamic="assuming no"
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+extern void $link_test_func (); void (*fptr) () = $link_test_func;
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_run "$LINENO"; then :
+  pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl__export_dynamic=yes
+else
+  pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl__export_dynamic=no
+fi
+rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
+  conftest.$ac_objext conftest.beam conftest.$ac_ext
+fi
+
+LDFLAGS="$pgac_save_LDFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl__export_dynamic" >&5
+$as_echo "$pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl__export_dynamic" >&6; }
+if test x"$pgac_cv_prog_cc_LDFLAGS_EX_BE__Wl__export_dynamic" = x"yes"; then
+  LDFLAGS_EX_BE="${LDFLAGS_EX_BE} -Wl,-export_dynamic"
+fi
+
+fi
 
 
 # Create compiler version string
diff --git a/configure.ac b/configure.ac
index 63e7be38472..72e3c1d429b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2423,7 +2423,11 @@ fi
 # For linkers that understand --export-dynamic, add that to the LDFLAGS_EX_BE
 # (backend specific ldflags). One some platforms this will always fail (e.g.,
 # windows), but on others it depends on the choice of linker (e.g., solaris).
+# macos uses -export_dynamic instead.
 PGAC_PROG_CC_LD_VARFLAGS_OPT(LDFLAGS_EX_BE, [-Wl,--export-dynamic], $link_test_func)
+if test x"$LDFLAGS_EX_BE" = x""; then
+  PGAC_PROG_CC_LD_VARFLAGS_OPT(LDFLAGS_EX_BE, [-Wl,-export_dynamic], $link_test_func)
+fi
 AC_SUBST(LDFLAGS_EX_BE)
 
 # Create compiler version string
-- 
2.45.1