Re: meson: Specify -Wformat as a common warning flag for extensions

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From: Tristan Partin <[email protected]>
To: Sutou Kouhei <[email protected]>
Cc: [email protected]
Subject: Re: meson: Specify -Wformat as a common warning flag for extensions
Date: Thu, 07 Mar 2024 23:39:39 -0600
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

On Sun Jan 21, 2024 at 11:11 PM CST, Sutou Kouhei wrote:
> Hi,
>
> I'm an extension developer. If I use PostgreSQL built with
> Meson, I get the following warning:
>
>     cc1: warning: '-Wformat-security' ignored without '-Wformat' [-Wformat-security]
>
> Because "pg_config --cflags" includes -Wformat-security but
> doesn't include -Wformat.
>
> Can we specify -Wformat as a common warning flag too? If we
> do it, "pg_config --cflags" includes both of
> -Wformat-security and -Wformat. So I don't get the warning.

The GCC documentation[0] says the following:

> If -Wformat is specified, also warn about uses of format functions 
> that represent possible security problems. At present, this warns 
> about calls to printf and scanf functions where the format string is 
> not a string literal and there are no format arguments, as in printf 
> (foo);. This may be a security hole if the format string came from 
> untrusted input and contains ‘%n’. (This is currently a subset of what 
> -Wformat-nonliteral warns about, but in future warnings may be added 
> to -Wformat-security that are not included in -Wformat-nonliteral.)

It sounds like a legitimate issue. I have confirmed the issue exists 
with a pg_config compiled with Meson. I can also confirm that this issue 
exists in the autotools build.

Here is a v2 of your patch which includes the fix for autotools. I will 
mark this "Ready for Committer" in the commitfest. Thanks!

[0]: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

-- 
Tristan Partin
Neon (https://neon.tech)


Attachments:

  [text/x-patch] v2-0001-Add-Wformat-to-common-warning-flags.patch (4.8K, ../[email protected]/2-v2-0001-Add-Wformat-to-common-warning-flags.patch)
  download | inline diff:
From bce0f70f866bb0e3f8fb8eb14c05bbbdd27c51f2 Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <[email protected]>
Date: Mon, 22 Jan 2024 13:51:58 +0900
Subject: [PATCH v2] Add -Wformat to common warning flags

We specify -Wformat-security as a common warning flag explicitly. GCC
requires -Wformat to be added for -Wformat-security to take effect. If
-Wformat-security is used without -Wformat, GCC shows the following
warning:

    cc1: warning: '-Wformat-security' ignored without '-Wformat' [-Wformat-security]

Co-authored-by: Sutou Kouhei <[email protected]>
---
 configure    | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 configure.ac |  3 ++
 meson.build  |  2 ++
 3 files changed, 97 insertions(+)

diff --git a/configure b/configure
index 36feeafbb23..eafab247e1d 100755
--- a/configure
+++ b/configure
@@ -5985,6 +5985,98 @@ if test x"$pgac_cv_prog_CXX_cxxflags__Wshadow_compatible_local" = x"yes"; then
 fi
 
 
+  # -Wformat-security requires -Wformat, so check for it
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wformat, for CFLAGS" >&5
+$as_echo_n "checking whether ${CC} supports -Wformat, for CFLAGS... " >&6; }
+if ${pgac_cv_prog_CC_cflags__Wformat+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+pgac_save_CC=$CC
+CC=${CC}
+CFLAGS="${CFLAGS} -Wformat"
+ac_save_c_werror_flag=$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__Wformat=yes
+else
+  pgac_cv_prog_CC_cflags__Wformat=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: $pgac_cv_prog_CC_cflags__Wformat" >&5
+$as_echo "$pgac_cv_prog_CC_cflags__Wformat" >&6; }
+if test x"$pgac_cv_prog_CC_cflags__Wformat" = x"yes"; then
+  CFLAGS="${CFLAGS} -Wformat"
+fi
+
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CXX} supports -Wformat, for CXXFLAGS" >&5
+$as_echo_n "checking whether ${CXX} supports -Wformat, for CXXFLAGS... " >&6; }
+if ${pgac_cv_prog_CXX_cxxflags__Wformat+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CXXFLAGS=$CXXFLAGS
+pgac_save_CXX=$CXX
+CXX=${CXX}
+CXXFLAGS="${CXXFLAGS} -Wformat"
+ac_save_cxx_werror_flag=$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__Wformat=yes
+else
+  pgac_cv_prog_CXX_cxxflags__Wformat=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: $pgac_cv_prog_CXX_cxxflags__Wformat" >&5
+$as_echo "$pgac_cv_prog_CXX_cxxflags__Wformat" >&6; }
+if test x"$pgac_cv_prog_CXX_cxxflags__Wformat" = x"yes"; then
+  CXXFLAGS="${CXXFLAGS} -Wformat"
+fi
+
+
   # This was included in -Wall/-Wformat in older GCC versions
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether ${CC} supports -Wformat-security, for CFLAGS" >&5
diff --git a/configure.ac b/configure.ac
index 57f734879e1..87a8860ecca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -527,6 +527,9 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CXX_CFLAGS_OPT([-Wcast-function-type])
   PGAC_PROG_CC_CFLAGS_OPT([-Wshadow=compatible-local])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wshadow=compatible-local])
+  # -Wformat-security requires -Wformat, so check for it
+  PGAC_PROG_CC_CFLAGS_OPT([-Wformat])
+  PGAC_PROG_CXX_CFLAGS_OPT([-Wformat])
   # This was included in -Wall/-Wformat in older GCC versions
   PGAC_PROG_CC_CFLAGS_OPT([-Wformat-security])
   PGAC_PROG_CXX_CFLAGS_OPT([-Wformat-security])
diff --git a/meson.build b/meson.build
index 85788f9dd8f..717fdc4746b 100644
--- a/meson.build
+++ b/meson.build
@@ -1826,6 +1826,8 @@ common_warning_flags = [
   '-Wimplicit-fallthrough=3',
   '-Wcast-function-type',
   '-Wshadow=compatible-local',
+  # -Wformat-security requires -Wformat, so check for it
+  '-Wformat',
   # This was included in -Wall/-Wformat in older GCC versions
   '-Wformat-security',
 ]
-- 
Tristan Partin
Neon (https://neon.tech)

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