From 8717f78997197a6cf28a01b2ef7f4ca0d1481b1b Mon Sep 17 00:00:00 2001
From: "Timo J. Rinne" <tri@iki.fi>
Date: Mon, 20 Jul 2026 17:36:30 +0300
Subject: [PATCH] Require a declaration before using explicit_bzero

A linked library can export explicit_bzero without declaring it in its public headers.  In that case the symbol check succeeds, but callers cannot compile because no prototype is available.

Check for the declaration separately and use PostgreSQL's replacement when it is absent.  Keep Autoconf and Meson behavior consistent.

Author: Timo J. Rinne <tri@iki.fi>
---
 configure                  | 27 ++++++++++++++++++++++++++-
 configure.ac               | 10 +++++++++-
 meson.build                |  5 ++++-
 src/include/pg_config.h.in |  4 ++++
 4 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index d42a7a794ff..04da7b7fee9 100755
--- a/configure
+++ b/configure
@@ -16347,6 +16347,18 @@ cat >>confdefs.h <<_ACEOF
 #define HAVE_DECL_TIMINGSAFE_BCMP $ac_have_decl
 _ACEOF
 
+ac_fn_c_check_decl "$LINENO" "explicit_bzero" "ac_cv_have_decl_explicit_bzero" "#include <string.h>
+"
+if test "x$ac_cv_have_decl_explicit_bzero" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_EXPLICIT_BZERO $ac_have_decl
+_ACEOF
+
 
 # We can't use AC_CHECK_FUNCS to detect these functions, because it
 # won't handle deployment target restrictions on macOS
@@ -16414,7 +16426,10 @@ cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
-ac_fn_c_check_func "$LINENO" "explicit_bzero" "ac_cv_func_explicit_bzero"
+# A linked library may export explicit_bzero without declaring it.  Do not
+# rely on such a symbol; use our replacement instead.
+if test "$ac_cv_have_decl_explicit_bzero" = yes; then
+  ac_fn_c_check_func "$LINENO" "explicit_bzero" "ac_cv_func_explicit_bzero"
 if test "x$ac_cv_func_explicit_bzero" = xyes; then :
   $as_echo "#define HAVE_EXPLICIT_BZERO 1" >>confdefs.h
 
@@ -16427,6 +16442,16 @@ esac
 
 fi
 
+
+else
+  case " $LIBOBJS " in
+  *" explicit_bzero.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS explicit_bzero.$ac_objext"
+ ;;
+esac
+
+fi
+
 ac_fn_c_check_func "$LINENO" "getopt" "ac_cv_func_getopt"
 if test "x$ac_cv_func_getopt" = xyes; then :
   $as_echo "#define HAVE_GETOPT 1" >>confdefs.h
diff --git a/configure.ac b/configure.ac
index a331749fcb5..7e721094fb9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1900,6 +1900,7 @@ AC_CHECK_DECLS(posix_fadvise, [], [], [#include <fcntl.h>])
 
 AC_CHECK_DECLS(fdatasync, [], [], [#include <unistd.h>])
 AC_CHECK_DECLS([strlcat, strlcpy, strsep, timingsafe_bcmp])
+AC_CHECK_DECLS([explicit_bzero], [], [], [#include <string.h>])
 
 # We can't use AC_CHECK_FUNCS to detect these functions, because it
 # won't handle deployment target restrictions on macOS
@@ -1912,8 +1913,15 @@ AC_CHECK_DECLS([memset_s], [], [], [#define __STDC_WANT_LIB_EXT1__ 1
 # This is probably only present on macOS, but may as well check always
 AC_CHECK_DECLS(F_FULLFSYNC, [], [], [#include <fcntl.h>])
 
+# A linked library may export explicit_bzero without declaring it.  Do not
+# rely on such a symbol; use our replacement instead.
+if test "$ac_cv_have_decl_explicit_bzero" = yes; then
+  AC_REPLACE_FUNCS([explicit_bzero])
+else
+  AC_LIBOBJ([explicit_bzero])
+fi
+
 AC_REPLACE_FUNCS(m4_normalize([
-	explicit_bzero
 	getopt
 	getpeereid
 	inet_aton
diff --git a/meson.build b/meson.build
index f4cde249242..63ecf6d8291 100644
--- a/meson.build
+++ b/meson.build
@@ -2886,6 +2886,7 @@ endforeach
 
 decl_checks = [
   ['F_FULLFSYNC', 'fcntl.h'],
+  ['explicit_bzero', 'string.h'],
   ['fdatasync', 'unistd.h'],
   ['posix_fadvise', 'fcntl.h'],
   ['strlcat', 'string.h'],
@@ -3197,7 +3198,9 @@ func_checks = [
   # required. Just checking for dlsym() ought to suffice.
   ['dlsym', {'dependencies': [dl_dep], 'define': false}],
   ['elf_aux_info'],
-  ['explicit_bzero'],
+  # A linked library may export explicit_bzero without declaring it.  Do not
+  # rely on such a symbol; use our replacement instead.
+  ['explicit_bzero', {'skip': cdata.get('HAVE_DECL_EXPLICIT_BZERO') == 0}],
   ['explicit_memset'],
   ['getauxval'],
   ['getifaddrs'],
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 661c4a9b168..4b8e88718d3 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -77,6 +77,10 @@
    similar. */
 #undef HAVE_CXX_TYPEOF_UNQUAL
 
+/* Define to 1 if you have the declaration of `explicit_bzero', and to 0 if
+   you don't. */
+#undef HAVE_DECL_EXPLICIT_BZERO
+
 /* Define to 1 if you have the declaration of `fdatasync', and to 0 if you
    don't. */
 #undef HAVE_DECL_FDATASYNC
-- 
2.50.1 (Apple Git-155)