Probe for preadv/pwritev in a more macOS-friendly way.

Apple's mechanism for dealing with functions that are available
in only some OS versions confuses AC_CHECK_FUNCS, and therefore
AC_REPLACE_FUNCS.  We can use AC_CHECK_DECLS instead, so long as
we enable -Werror=unguarded-availability-new.  This allows people
compiling for macOS to control whether or not preadv/pwritev are
used by setting MACOSX_DEPLOYMENT_TARGET, rather than supplying
a back-rev SDK.  (Of course, the latter still works, too.)

James Hilliard

Discussion: https://postgr.es/m/20210122193230.25295-1-james.hilliard1@gmail.com

configure

@@ -5383,6 +5383,98 @@ if test x"$pgac_cv_prog_CC_cflags__Werror_vla" = x"yes"; then
 fi
 
 
+  # On macOS, complain about usage of symbols newer than the deployment target
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Werror=unguarded-availability-new, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Werror=unguarded-availability-new, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CC}
+CFLAGS="${CFLAGS} -Werror=unguarded-availability-new"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new=yes
+else
+  pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+CC="$pgac_save_CC"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Werror_unguarded_availability_new" = x"yes"; then
+  CFLAGS="${CFLAGS} -Werror=unguarded-availability-new"
+fi
+
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Werror=unguarded-availability-new, for CXXFLAGS" >&5
+$as_echo_n "checking whether ${CXX} supports -Werror=unguarded-availability-new, for CXXFLAGS... " >&6; }
+if ${pgac_cv_prog_CXX_cxxflags__Werror_unguarded_availability_new+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CXXFLAGS=$CXXFLAGS
+pgac_save_CXX=$CXX
+CXX=${CXX}
+CXXFLAGS="${CXXFLAGS} -Werror=unguarded-availability-new"
+ac_save_cxx_werror_flag=$ac_cxx_werror_flag
+ac_cxx_werror_flag=yes
+ac_ext=cpp
+ac_cpp='$CXXCPP $CPPFLAGS'
+ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
+
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  pgac_cv_prog_CXX_cxxflags__Werror_unguarded_availability_new=yes
+else
+  pgac_cv_prog_CXX_cxxflags__Werror_unguarded_availability_new=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+ac_cxx_werror_flag=$ac_save_cxx_werror_flag
+CXXFLAGS="$pgac_save_CXXFLAGS"
+CXX="$pgac_save_CXX"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_CXX_cxxflags__Werror_unguarded_availability_new" >&5
+$as_echo "$pgac_cv_prog_CXX_cxxflags__Werror_unguarded_availability_new" >&6; }
+if test x"$pgac_cv_prog_CXX_cxxflags__Werror_unguarded_availability_new" = x"yes"; then
+  CXXFLAGS="${CXXFLAGS} -Werror=unguarded-availability-new"
+fi
+
+
   # -Wvla is not applicable for C++
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wendif-labels, for CFLAGS" >&5
@@ -15931,6 +16023,54 @@ cat >>confdefs.h <<_ACEOF
 #define HAVE_DECL_STRNLEN $ac_have_decl
 _ACEOF
 
+
+# We can't use AC_REPLACE_FUNCS to replace these functions, because it
+# won't handle deployment target restrictions on macOS
+ac_fn_c_check_decl "$LINENO" "preadv" "ac_cv_have_decl_preadv" "#include <sys/uio.h>
+"
+if test "x$ac_cv_have_decl_preadv" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_PREADV $ac_have_decl
+_ACEOF
+if test $ac_have_decl = 1; then :
+
+else
+  case " $LIBOBJS " in
+  *" preadv.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS preadv.$ac_objext"
+ ;;
+esac
+
+fi
+
+ac_fn_c_check_decl "$LINENO" "pwritev" "ac_cv_have_decl_pwritev" "#include <sys/uio.h>
+"
+if test "x$ac_cv_have_decl_pwritev" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_PWRITEV $ac_have_decl
+_ACEOF
+if test $ac_have_decl = 1; then :
+
+else
+  case " $LIBOBJS " in
+  *" pwritev.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS pwritev.$ac_objext"
+ ;;
+esac
+
+fi
+
+
 # This is probably only present on macOS, but may as well check always
 ac_fn_c_check_decl "$LINENO" "F_FULLFSYNC" "ac_cv_have_decl_F_FULLFSYNC" "#include <fcntl.h>
 "
@@ -16144,19 +16284,6 @@ esac
 
 fi
 
-ac_fn_c_check_func "$LINENO" "preadv" "ac_cv_func_preadv"
-if test "x$ac_cv_func_preadv" = xyes; then :
-  $as_echo "#define HAVE_PREADV 1" >>confdefs.h
-
-else
-  case " $LIBOBJS " in
-  *" preadv.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS preadv.$ac_objext"
- ;;
-esac
-
-fi
-
 ac_fn_c_check_func "$LINENO" "pwrite" "ac_cv_func_pwrite"
 if test "x$ac_cv_func_pwrite" = xyes; then :
   $as_echo "#define HAVE_PWRITE 1" >>confdefs.h
@@ -16170,19 +16297,6 @@ esac
 
 fi
 
-ac_fn_c_check_func "$LINENO" "pwritev" "ac_cv_func_pwritev"
-if test "x$ac_cv_func_pwritev" = xyes; then :
-  $as_echo "#define HAVE_PWRITEV 1" >>confdefs.h
-
-else
-  case " $LIBOBJS " in
-  *" pwritev.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS pwritev.$ac_objext"
- ;;
-esac
-
-fi
-
 ac_fn_c_check_func "$LINENO" "random" "ac_cv_func_random"
 if test "x$ac_cv_func_random" = xyes; then :
   $as_echo "#define HAVE_RANDOM 1" >>confdefs.h

configure.ac

@@ -494,6 +494,9 @@ if test "$GCC" = yes -a "$ICC" = no; then
   AC_SUBST(PERMIT_DECLARATION_AFTER_STATEMENT)
   # Really don't want VLAs to be used in our dialect of C
   PGAC_PROG_CC_CFLAGS_OPT([-Werror=vla])
+  # On macOS, complain about usage of symbols newer than the deployment target
+  PGAC_PROG_CC_CFLAGS_OPT([-Werror=unguarded-availability-new])
+  PGAC_PROG_CXX_CFLAGS_OPT([-Werror=unguarded-availability-new])
   # -Wvla is not applicable for C++
   PGAC_PROG_CC_CFLAGS_OPT([-Wendif-labels])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wendif-labels])
@@ -1749,6 +1752,12 @@ AC_CHECK_DECLS(posix_fadvise, [], [], [#include <fcntl.h>])
 
 AC_CHECK_DECLS(fdatasync, [], [], [#include <unistd.h>])
 AC_CHECK_DECLS([strlcat, strlcpy, strnlen])
+
+# We can't use AC_REPLACE_FUNCS to replace these functions, because it
+# won't handle deployment target restrictions on macOS
+AC_CHECK_DECLS([preadv], [], [AC_LIBOBJ(preadv)], [#include <sys/uio.h>])
+AC_CHECK_DECLS([pwritev], [], [AC_LIBOBJ(pwritev)], [#include <sys/uio.h>])
+
 # This is probably only present on macOS, but may as well check always
 AC_CHECK_DECLS(F_FULLFSYNC, [], [], [#include <fcntl.h>])
 
@@ -1784,9 +1793,7 @@ AC_REPLACE_FUNCS(m4_normalize([
 	link
 	mkdtemp
 	pread
-	preadv
 	pwrite
-	pwritev
 	random
 	srandom
 	strlcat

src/include/pg_config.h.in

@@ -142,6 +142,14 @@
    don't. */
 #undef HAVE_DECL_POSIX_FADVISE
 
+/* Define to 1 if you have the declaration of `preadv', and to 0 if you don't.
+   */
+#undef HAVE_DECL_PREADV
+
+/* Define to 1 if you have the declaration of `pwritev', and to 0 if you
+   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
@@ -421,9 +429,6 @@
 /* Define to 1 if you have the `pread' function. */
 #undef HAVE_PREAD
 
-/* Define to 1 if you have the `preadv' function. */
-#undef HAVE_PREADV
-
 /* Define to 1 if you have the `pstat' function. */
 #undef HAVE_PSTAT
 
@@ -445,9 +450,6 @@
 /* Define to 1 if you have the `pwrite' function. */
 #undef HAVE_PWRITE
 
-/* Define to 1 if you have the `pwritev' function. */
-#undef HAVE_PWRITEV
-
 /* Define to 1 if you have the `random' function. */
 #undef HAVE_RANDOM
 

src/include/port/pg_iovec.h

@@ -39,13 +39,13 @@ struct iovec
 /* Define a reasonable maximum that is safe to use on the stack. */
 #define PG_IOV_MAX Min(IOV_MAX, 32)
 
-#ifdef HAVE_PREADV
+#if HAVE_DECL_PREADV
 #define pg_preadv preadv
 #else
 extern ssize_t pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset);
 #endif
 
-#ifdef HAVE_PWRITEV
+#if HAVE_DECL_PWRITEV
 #define pg_pwritev pwritev
 #else
 extern ssize_t pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset);

src/tools/msvc/Solution.pm

@@ -245,6 +245,8 @@ sub GenerateFiles
 		HAVE_DECL_LLVMGETHOSTCPUFEATURES            => 0,
 		HAVE_DECL_LLVMORCGETSYMBOLADDRESSIN         => 0,
 		HAVE_DECL_POSIX_FADVISE                     => undef,
+		HAVE_DECL_PREADV                            => 0,
+		HAVE_DECL_PWRITEV                           => 0,
 		HAVE_DECL_RTLD_GLOBAL                       => 0,
 		HAVE_DECL_RTLD_NOW                          => 0,
 		HAVE_DECL_STRLCAT                           => undef,
@@ -335,7 +337,6 @@ sub GenerateFiles
 		HAVE_PPC_LWARX_MUTEX_HINT   => undef,
 		HAVE_PPOLL                  => undef,
 		HAVE_PREAD                  => undef,
-		HAVE_PREADV                 => undef,
 		HAVE_PSTAT                  => undef,
 		HAVE_PS_STRINGS             => undef,
 		HAVE_PTHREAD                => undef,
@@ -343,7 +344,6 @@ sub GenerateFiles
 		HAVE_PTHREAD_IS_THREADED_NP => undef,
 		HAVE_PTHREAD_PRIO_INHERIT   => undef,
 		HAVE_PWRITE                 => undef,
-		HAVE_PWRITEV                => undef,
 		HAVE_RANDOM                 => undef,
 		HAVE_READLINE_H             => undef,
 		HAVE_READLINE_HISTORY_H     => undef,