Allow PG_PRINTF_ATTRIBUTE to be different in C and C++ code.

Although clang claims to be compatible with gcc's printf format
archetypes, this appears to be a falsehood: it likes __syslog__
(which gcc does not, on most platforms) and doesn't accept
gnu_printf.  This means that if you try to use gcc with clang++
or clang with g++, you get compiler warnings when compiling
printf-like calls in our C++ code.  This has been true for quite
awhile, but it's gotten more annoying with the recent appearance
of several buildfarm members that are configured like this.

To fix, run separate probes for the format archetype to use with the
C and C++ compilers, and conditionally define PG_PRINTF_ATTRIBUTE
depending on __cplusplus.

(We could alternatively insist that you not mix-and-match C and
C++ compilers; but if the case works otherwise, this is a poor
reason to insist on that.)

No back-patch for now, but we may want to do that if this
patch survives buildfarm testing.

Discussion: https://postgr.es/m/986485.1764825548@sss.pgh.pa.us

diff --git a/config/c-compiler.m4 b/config/c-compiler.m4
index 236a59e8536c2ea31a8ac80d8a3808c23a75c893..e309a5e3e40acd08f818121b28a3459d5f937a67 100644 (file)
--- a/config/c-compiler.m4
+++ b/config/c-compiler.m4
@@ -7,10 +7,10 @@
 # Select the format archetype to be used by gcc to check printf-type functions.
 # We prefer "gnu_printf", as that most closely matches the features supported
 # by src/port/snprintf.c (particularly the %m conversion spec).  However,
-# on some NetBSD versions, that doesn't work while "__syslog__" does.
-# If all else fails, use "printf".
+# on clang and on some NetBSD versions, that doesn't work while "__syslog__"
+# does.  If all else fails, use "printf".
 AC_DEFUN([PGAC_PRINTF_ARCHETYPE],
-[AC_CACHE_CHECK([for printf format archetype], pgac_cv_printf_archetype,
+[AC_CACHE_CHECK([for C printf format archetype], pgac_cv_printf_archetype,
 [pgac_cv_printf_archetype=gnu_printf
 PGAC_TEST_PRINTF_ARCHETYPE
 if [[ "$ac_archetype_ok" = no ]]; then
@@ -20,8 +20,8 @@ if [[ "$ac_archetype_ok" = no ]]; then
     pgac_cv_printf_archetype=printf
   fi
 fi])
-AC_DEFINE_UNQUOTED([PG_PRINTF_ATTRIBUTE], [$pgac_cv_printf_archetype],
-[Define to best printf format archetype, usually gnu_printf if available.])
+AC_DEFINE_UNQUOTED([PG_C_PRINTF_ATTRIBUTE], [$pgac_cv_printf_archetype],
+[Define to best C printf format archetype, usually gnu_printf if available.])
 ])# PGAC_PRINTF_ARCHETYPE
 
 # Subroutine: test $pgac_cv_printf_archetype, set $ac_archetype_ok to yes or no
@@ -38,6 +38,42 @@ ac_c_werror_flag=$ac_save_c_werror_flag
 ])# PGAC_TEST_PRINTF_ARCHETYPE
 
 
+# PGAC_CXX_PRINTF_ARCHETYPE
+# -------------------------
+# Because we support using gcc as C compiler with clang as C++ compiler,
+# we have to be prepared to use different printf archetypes in C++ code.
+# So, do the above test all over in C++.
+AC_DEFUN([PGAC_CXX_PRINTF_ARCHETYPE],
+[AC_CACHE_CHECK([for C++ printf format archetype], pgac_cv_cxx_printf_archetype,
+[pgac_cv_cxx_printf_archetype=gnu_printf
+PGAC_TEST_CXX_PRINTF_ARCHETYPE
+if [[ "$ac_archetype_ok" = no ]]; then
+  pgac_cv_cxx_printf_archetype=__syslog__
+  PGAC_TEST_CXX_PRINTF_ARCHETYPE
+  if [[ "$ac_archetype_ok" = no ]]; then
+    pgac_cv_cxx_printf_archetype=printf
+  fi
+fi])
+AC_DEFINE_UNQUOTED([PG_CXX_PRINTF_ATTRIBUTE], [$pgac_cv_cxx_printf_archetype],
+[Define to best C++ printf format archetype, usually gnu_printf if available.])
+])# PGAC_CXX_PRINTF_ARCHETYPE
+
+# Subroutine: test $pgac_cv_cxx_printf_archetype, set $ac_archetype_ok to yes or no
+AC_DEFUN([PGAC_TEST_CXX_PRINTF_ARCHETYPE],
+[ac_save_cxx_werror_flag=$ac_cxx_werror_flag
+ac_cxx_werror_flag=yes
+AC_LANG_PUSH(C++)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+[extern void pgac_write(int ignore, const char *fmt,...)
+__attribute__((format($pgac_cv_cxx_printf_archetype, 2, 3)));],
+[pgac_write(0, "error %s: %m", "foo");])],
+                  [ac_archetype_ok=yes],
+                  [ac_archetype_ok=no])
+AC_LANG_POP([])
+ac_cxx_werror_flag=$ac_save_cxx_werror_flag
+])# PGAC_TEST_CXX_PRINTF_ARCHETYPE
+
+
 # PGAC_TYPE_128BIT_INT
 # --------------------
 # Check if __int128 is a working 128 bit integer type, and if so

diff --git a/configure b/configure
index 3f91117f2457384a5114665c009b76bdcbaf693a..5ee3c265b1c1f9a709cf5d9295756f06d07430fe 100755 (executable)
--- a/configure
+++ b/configure
@@ -14691,8 +14691,8 @@ _ACEOF
     ;;
 esac
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for printf format archetype" >&5
-$as_echo_n "checking for printf format archetype... " >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for C printf format archetype" >&5
+$as_echo_n "checking for C printf format archetype... " >&6; }
 if ${pgac_cv_printf_archetype+:} false; then :
   $as_echo_n "(cached) " >&6
 else
@@ -14752,7 +14752,97 @@ fi
 $as_echo "$pgac_cv_printf_archetype" >&6; }
 
 cat >>confdefs.h <<_ACEOF
-#define PG_PRINTF_ATTRIBUTE $pgac_cv_printf_archetype
+#define PG_C_PRINTF_ATTRIBUTE $pgac_cv_printf_archetype
+_ACEOF
+
+
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for C++ printf format archetype" >&5
+$as_echo_n "checking for C++ printf format archetype... " >&6; }
+if ${pgac_cv_cxx_printf_archetype+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_cv_cxx_printf_archetype=gnu_printf
+ac_save_cxx_werror_flag=$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.$ac_ext
+/* end confdefs.h.  */
+extern void pgac_write(int ignore, const char *fmt,...)
+__attribute__((format($pgac_cv_cxx_printf_archetype, 2, 3)));
+int
+main ()
+{
+pgac_write(0, "error %s: %m", "foo");
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  ac_archetype_ok=yes
+else
+  ac_archetype_ok=no
+fi
+rm -f core conftest.err conftest.$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=$ac_save_cxx_werror_flag
+
+if [ "$ac_archetype_ok" = no ]; then
+  pgac_cv_cxx_printf_archetype=__syslog__
+  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.$ac_ext
+/* end confdefs.h.  */
+extern void pgac_write(int ignore, const char *fmt,...)
+__attribute__((format($pgac_cv_cxx_printf_archetype, 2, 3)));
+int
+main ()
+{
+pgac_write(0, "error %s: %m", "foo");
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  ac_archetype_ok=yes
+else
+  ac_archetype_ok=no
+fi
+rm -f core conftest.err conftest.$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=$ac_save_cxx_werror_flag
+
+  if [ "$ac_archetype_ok" = no ]; then
+    pgac_cv_cxx_printf_archetype=printf
+  fi
+fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_cxx_printf_archetype" >&5
+$as_echo "$pgac_cv_cxx_printf_archetype" >&6; }
+
+cat >>confdefs.h <<_ACEOF
+#define PG_CXX_PRINTF_ATTRIBUTE $pgac_cv_cxx_printf_archetype
 _ACEOF
 
 

diff --git a/configure.ac b/configure.ac
index 8f39002740331921a4c86b3a51d50305ee4b140c..4ba3967db0fe64560ab64f3b556009dee44b05fe 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1676,6 +1676,7 @@ m4_defun([AC_PROG_CC_STDC], []) dnl We don't want that.
 AC_C_BIGENDIAN
 AC_C_INLINE
 PGAC_PRINTF_ARCHETYPE
+PGAC_CXX_PRINTF_ARCHETYPE
 PGAC_C_STATIC_ASSERT
 PGAC_C_TYPEOF
 PGAC_C_TYPES_COMPATIBLE

diff --git a/meson.build b/meson.build
index 718150e3ac01f096d017dd70a26c3f112a1b7f49..1256094fa571c6348bdf203a7963df3c84721f68 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -1897,6 +1897,8 @@ if cc.compiles('''
 endif
 
 
+# Select the format archetype to be used to check printf-type functions.
+#
 # Need to check a call with %m because netbsd supports gnu_printf but emits a
 # warning for each use of %m.
 printf_attributes = ['gnu_printf', '__syslog__', 'printf']
@@ -1911,11 +1913,24 @@ attrib_error_args = cc.get_supported_arguments('-Werror=format', '-Werror=ignore
 foreach a : printf_attributes
   if cc.compiles(testsrc.format(a),
       args: test_c_args + attrib_error_args, name: 'format ' + a)
-    cdata.set('PG_PRINTF_ATTRIBUTE', a)
+    cdata.set('PG_C_PRINTF_ATTRIBUTE', a)
     break
   endif
 endforeach
 
+# We need to repeat the test for C++ because gcc and clang prefer different
+# format archetypes.
+if llvm.found()
+  attrib_error_args = cpp.get_supported_arguments('-Werror=format', '-Werror=ignored-attributes')
+  foreach a : printf_attributes
+    if cpp.compiles(testsrc.format(a),
+        args: attrib_error_args, name: 'cppformat ' + a)
+      cdata.set('PG_CXX_PRINTF_ATTRIBUTE', a)
+      break
+    endif
+  endforeach
+endif
+
 
 if cc.has_function_attribute('visibility:default') and \
     cc.has_function_attribute('visibility:hidden')

diff --git a/src/include/c.h b/src/include/c.h
index 62cbf7a2eec20df1e8ce6064c6d675fce3e45154..55effdda0fd658fa17fcab8db899c04cb92bf2f3 100644 (file)
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -228,6 +228,16 @@
 #define PG_USED_FOR_ASSERTS_ONLY pg_attribute_unused()
 #endif
 
+/*
+ * Our C and C++ compilers may have different ideas about which printf
+ * archetype best represents what src/port/snprintf.c can do.
+ */
+#ifndef __cplusplus
+#define PG_PRINTF_ATTRIBUTE PG_C_PRINTF_ATTRIBUTE
+#else
+#define PG_PRINTF_ATTRIBUTE PG_CXX_PRINTF_ATTRIBUTE
+#endif
+
 /* GCC supports format attributes */
 #if defined(__GNUC__)
 #define pg_attribute_format_arg(a) __attribute__((format_arg(a)))

diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 72434ce957edaae4e01b427a7aacaff366dc1871..3a7edb1f0a02a6aecdcf13e34eef4da3548ce491 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -596,6 +596,14 @@
 /* Define to the version of this package. */
 #undef PACKAGE_VERSION
 
+/* Define to best C++ printf format archetype, usually gnu_printf if
+   available. */
+#undef PG_CXX_PRINTF_ATTRIBUTE
+
+/* Define to best C printf format archetype, usually gnu_printf if available.
+   */
+#undef PG_C_PRINTF_ATTRIBUTE
+
 /* Define to the name of a signed 128-bit integer type. */
 #undef PG_INT128_TYPE
 
@@ -612,9 +620,6 @@
 /* PostgreSQL minor version number */
 #undef PG_MINORVERSION_NUM
 
-/* Define to best printf format archetype, usually gnu_printf if available. */
-#undef PG_PRINTF_ATTRIBUTE
-
 /* PostgreSQL version as a string */
 #undef PG_VERSION