Make -Wformat-nonliteral work with gcc

After looking into why the build failed for Simon but not for me, we
found that the underlying cause was due to how gcc treats
-Wformat-nonliteral.  gcc requires -Wformat to be given first; but
warning.m4 was not doing this, so -Wformat-nonliteral was not being
used.

This patch changes warning.m4 to account gcc's requirement.

This then showed that the target-float.c build change in the earlier
Makefile patch was also incorrect.  Simon didn't see this in his
build, but gcc now points it out.  So, this patch fixes this problem
as well.

2018-09-05  Tom Tromey  <tom@tromey.com>

	* warning.m4 (AM_GDB_WARNINGS): Add -Wformat when testing
	-Wformat-nonliteral.
	* target-float.c (host_float_ops<T>::to_string)
	(host_float_ops<T>::from_string): Use
	DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL.
	* configure: Rebuild.

gdb/gdbserver/ChangeLog
2018-09-05  Tom Tromey  <tom@tromey.com>

	* configure: Rebuild.

6 files changed, 50 insertions, 3 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d8ca6d3dabd..69e3182ec32 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2018-09-05  Tom Tromey  <tom@tromey.com>
+
+	* warning.m4 (AM_GDB_WARNINGS): Add -Wformat when testing
+	-Wformat-nonliteral.
+	* target-float.c (host_float_ops<T>::to_string)
+	(host_float_ops<T>::from_string): Use
+	DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL.
+	* configure: Rebuild.
+
 2018-09-05  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* printcmd.c (printf_c_string): Use
diff --git a/gdb/configure b/gdb/configure
index 270657103b6..d92a256f1ff 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -15427,7 +15427,10 @@ case "${host}" in
     build_warnings="$build_warnings -Wno-unknown-pragmas"
     # Solaris 11 <unistd.h> marks vfork deprecated.
     build_warnings="$build_warnings -Wno-deprecated-declarations" ;;
-  *) build_warnings="$build_warnings -Wformat-nonliteral" ;;
+  *)
+    # Note that gcc requires -Wformat for -Wformat-nonliteral to work,
+    # but there's a special case for this below.
+    build_warnings="$build_warnings -Wformat-nonliteral" ;;
 esac
 
 # Check whether --enable-build-warnings was given.
@@ -15483,6 +15486,12 @@ $as_echo_n "checking compiler warning flags... " >&6; }
 	case $w in
 	-Wno-*)
 		wtest=`echo $w | sed 's/-Wno-/-W/g'` ;;
+        -Wformat-nonliteral)
+		# gcc requires -Wformat before -Wformat-nonliteral
+		# will work, so stick them together.
+		w="-Wformat $w"
+		wtest="$w"
+		;;
 	*)
 		wtest=$w ;;
 	esac
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index cd0318c79aa..0c5c32b22ef 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,7 @@
+2018-09-05  Tom Tromey  <tom@tromey.com>
+
+	* configure: Rebuild.
+
 2018-08-28  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	PR build/23399
diff --git a/gdb/gdbserver/configure b/gdb/gdbserver/configure
index 7454cd8ad37..f5cbbaea78a 100755
--- a/gdb/gdbserver/configure
+++ b/gdb/gdbserver/configure
@@ -7258,7 +7258,10 @@ case "${host}" in
     build_warnings="$build_warnings -Wno-unknown-pragmas"
     # Solaris 11 <unistd.h> marks vfork deprecated.
     build_warnings="$build_warnings -Wno-deprecated-declarations" ;;
-  *) build_warnings="$build_warnings -Wformat-nonliteral" ;;
+  *)
+    # Note that gcc requires -Wformat for -Wformat-nonliteral to work,
+    # but there's a special case for this below.
+    build_warnings="$build_warnings -Wformat-nonliteral" ;;
 esac
 
 # Check whether --enable-build-warnings was given.
@@ -7314,6 +7317,12 @@ $as_echo_n "checking compiler warning flags... " >&6; }
 	case $w in
 	-Wno-*)
 		wtest=`echo $w | sed 's/-Wno-/-W/g'` ;;
+        -Wformat-nonliteral)
+		# gcc requires -Wformat before -Wformat-nonliteral
+		# will work, so stick them together.
+		w="-Wformat $w"
+		wtest="$w"
+		;;
 	*)
 		wtest=$w ;;
 	esac
diff --git a/gdb/target-float.c b/gdb/target-float.c
index c2878cb0a08..a12f216b53d 100644
--- a/gdb/target-float.c
+++ b/gdb/target-float.c
@@ -948,7 +948,11 @@ host_float_ops<T>::to_string (const gdb_byte *addr, const struct type *type,
 
   T host_float;
   from_target (type, addr, &host_float);
+
+  DIAGNOSTIC_PUSH
+  DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
   return string_printf (host_format.c_str (), host_float);
+  DIAGNOSTIC_POP
 }
 
 /* Parse string IN into a target floating-number of type TYPE and
@@ -977,7 +981,10 @@ host_float_ops<T>::from_string (gdb_byte *addr, const struct type *type,
     scan_format += scanf_length_modifier<T>::value;
   scan_format += "g%n";
 
+  DIAGNOSTIC_PUSH
+  DIAGNOSTIC_IGNORE_FORMAT_NONLITERAL
   num = sscanf (in.c_str (), scan_format.c_str(), &host_float, &n);
+  DIAGNOSTIC_POP
 
   /* The sscanf man page suggests not making any assumptions on the effect
      of %n on the result, so we don't.
diff --git a/gdb/warning.m4 b/gdb/warning.m4
index dd338493f9e..82170acc802 100644
--- a/gdb/warning.m4
+++ b/gdb/warning.m4
@@ -58,7 +58,10 @@ case "${host}" in
     build_warnings="$build_warnings -Wno-unknown-pragmas"
     # Solaris 11 <unistd.h> marks vfork deprecated.
     build_warnings="$build_warnings -Wno-deprecated-declarations" ;;
-  *) build_warnings="$build_warnings -Wformat-nonliteral" ;;
+  *)
+    # Note that gcc requires -Wformat for -Wformat-nonliteral to work,
+    # but there's a special case for this below.
+    build_warnings="$build_warnings -Wformat-nonliteral" ;;
 esac
 
 AC_ARG_ENABLE(build-warnings,
@@ -106,6 +109,12 @@ then
 	case $w in
 	-Wno-*)
 		wtest=`echo $w | sed 's/-Wno-/-W/g'` ;;
+        -Wformat-nonliteral)
+		# gcc requires -Wformat before -Wformat-nonliteral
+		# will work, so stick them together.
+		w="-Wformat $w"
+		wtest="$w"
+		;;
 	*)
 		wtest=$w ;;
 	esac