Add --enable-build-with-cxx configure switch

This new option, disabled by default for now, allows specifying
whether to build GDB, GDBserver, and friends with a C++ (98/03)
compiler.

The name of the switch should be familiar to those who followed GCC's
own C++ conversion process.

. Adding -fpermissive to COMPILER in C++ mode (see the new
build-with-cxx.m4 file) makes errors like these be warnings instead:

  gdb/infrun.c:6597:1: error:   initializing argument 1 of ‘void sig_print_info(gdb_signal)’ [-fpermissive]
   sig_print_info (enum gdb_signal oursig)
   ^
  gdb/infrun.c: In function ‘void do_restore_infcall_suspend_state_cleanup(void*)’:
  gdb/infrun.c:7164:39: error: invalid conversion from ‘void*’ to ‘infcall_suspend_state*’ [-fpermissive]
     restore_infcall_suspend_state (state);
				 ^

so that the compiler carries on compiling the file.  -Werror still
catches the warnings, so nothing is lost, only our lifes are made
easier by concentrating on getting other more important things out of
the way first.

There's no way to quiet those warnings.  Until they're all fixed, when
building in C++ mode, -Werror is disabled by default.

. Adding -Wno-narrowing suppresses thousands of instances of this warning:

  gdb/arm-linux-tdep.c:439:1: error: narrowing conversion of ‘-1’ from ‘int’ to ‘ULONGEST {aka long unsigned int}’ inside { } is ill-formed in C++11 [-Werror=narrowing]
  gdb/arm-linux-tdep.c:439:1: error: narrowing conversion of ‘-1l’ from ‘LONGEST {aka long int}’ to ‘ULONGEST {aka long unsigned int}’ inside { } is ill-formed in C++11 [-Werror=narrowing]
  gdb/arm-linux-tdep.c:450:1: error: narrowing conversion of ‘-1’ from ‘int’ to ‘ULONGEST {aka long unsigned int}’ inside { } is ill-formed in C++11 [-Werror=narrowing]

We can defer handling those until we target C++11.


. Adding -Wno-sign-compare suppresses thousands of instances of this warning:

  gdb/linux-record.c:1763:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
	 if (tmpulongest == tdep->fcntl_F_GETLK64)
				  ^


. Adding -Wno-write-strings suppresses thousands of instances of this warning:

  gdb/mi/mi-cmd-var.c: In function ‘void mi_cmd_var_show_attributes(char*, char**, int)’:
  gdb/mi/mi-cmd-var.c:514:12: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
       attstr = "editable";
	      ^
  gdb/mi/mi-cmd-var.c:516:12: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
       attstr = "noneditable";
	      ^

For now, it's best to hide these warnings from view until we're
'-fpermissive'-clean, and can thus start building with -Werror.
The C compiler has always managed to build working GDBs with these
issues in the code, so a C++ compiler should too.

gdb/ChangeLog:
2015-02-27  Pedro Alves  <palves@redhat.com>

	* Makefile.in (COMPILER): New, get it from autoconf.
	(COMPILE.pre, CC_LD): Use COMPILER.
	(CXX): Get from autoconf instead.
	(CXX_FOR_TARGET): Default to g++ instead of gcc.
	* acinclude.m4: Include build-with-cxx.m4.
	* build-with-cxx.m4: New file.
	* configure.ac: Call AC_PROG_CXX and GDB_AC_BUILD_WITH_CXX.
	Disable -Werror by default if building in C++ mode.
	(build_warnings): Add -Wno-sign-compare, -Wno-write-strings and
	-Wno-narrowing in C++ mode.  Only enable -Wpointer-sign in C mode.
	Run supported-warning-flags tests with the C++ compiler.
	Save/restore CXXFLAGS too.
	* configure: Regenerate.

gdb/gdbserver/ChangeLog:
2015-02-27  Pedro Alves  <palves@redhat.com>

	* Makefile.in (COMPILER): New, get it from autoconf.
	(CXX): Get from autoconf instead.
	(COMPILE.pre): Use COMPILER.
	(CC-LD): Rename to ...
	(CC_LD): ... this.  Use COMPILER.
	(gdbserver$(EXEEXT), gdbreplay$(EXEEXT), $(IPA_LIB)): Adjust.
	(CXX_FOR_TARGET): Default to g++ instead of gcc.
	* acinclude.m4: Include build-with-cxx.m4.
	* configure.ac: Call AC_PROG_CXX and GDB_AC_BUILD_WITH_CXX.
	Disable -Werror by default if building in C++ mode.
	(build_warnings): Add -Wno-sign-compare, -Wno-write-strings and
	-Wno-narrowing in C++ mode. Run supported-warning-flags tests with
	the C++ compiler.  Save/restore CXXFLAGS too.
	* configure: Regenerate.

1 files changed, 35 insertions, 4 deletions

diff --git a/gdb/configure.ac b/gdb/configure.ac
index e72dfba..0898d0e 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -27,6 +27,8 @@ AM_MAINTAINER_MODE
 . $srcdir/../bfd/development.sh
 
 AC_PROG_CC
+AC_PROG_CXX
+
 AC_USE_SYSTEM_EXTENSIONS
 ACX_LARGEFILE
 AM_PROG_CC_STDC
@@ -36,6 +38,9 @@ AC_CONFIG_AUX_DIR(..)
 AC_CANONICAL_SYSTEM
 AC_ARG_PROGRAM
 
+# See if we are building with C++, and substitute COMPILER.
+GDB_AC_BUILD_WITH_CXX
+
 # Dependency checking.
 ZW_CREATE_DEPDIR
 ZW_PROG_COMPILER_DEPENDENCIES([CC])
@@ -1959,8 +1964,11 @@ AC_ARG_ENABLE(werror,
      *) AC_MSG_ERROR(bad value ${enableval} for --enable-werror) ;;
    esac])
 
-# Enable -Werror by default when using gcc.  Turn it off for releases.
-if test "${GCC}" = yes -a -z "${ERROR_ON_WARNING}" && $development; then
+# Enable -Werror by default when using gcc in C mode.  Leave it off
+# for C++ until we're warning clean.  Turn it off for releases.
+if test "${GCC}" = yes -a -z "${ERROR_ON_WARNING}" \
+   && test x"$enable_build_with_cxx" != x"yes" \
+   && $development; then
     ERROR_ON_WARNING=yes
 fi
 
@@ -1969,13 +1977,21 @@ if test "${ERROR_ON_WARNING}" = yes ; then
     WERROR_CFLAGS="-Werror"
 fi
 
+# These options work in either C or C++ modes.
 build_warnings="-Wall -Wdeclaration-after-statement -Wpointer-arith \
--Wpointer-sign \
 -Wno-unused -Wunused-value -Wunused-function \
 -Wno-switch -Wno-char-subscripts -Wmissing-prototypes \
 -Wdeclaration-after-statement -Wempty-body -Wmissing-parameter-type \
 -Wold-style-declaration -Wold-style-definition"
 
+# Now add in C and C++ specific options, depending on mode.
+if test "$enable_build_with_cxx" = "yes"; then
+   build_warnings="$build_warnings -Wno-sign-compare -Wno-write-strings \
+-Wno-narrowing"
+else
+   build_warnings="$build_warnings -Wpointer-sign"
+fi
+
 # Enable -Wno-format by default when using gcc on mingw since many
 # GCC versions complain about %I64.
 case "${host}" in
@@ -2011,6 +2027,13 @@ esac
 if test x"$silent" != x"yes" && test x"$build_warnings" != x""; then
   echo "Setting GDB specific compiler warning flags = $build_warnings" 6>&1
 fi])dnl
+
+# The set of warnings supported by a C++ compiler is not the same as
+# of the C compiler.
+if test "$enable_build_with_cxx" = "yes"; then
+    AC_LANG_PUSH([C++])
+fi
+
 WARN_CFLAGS=""
 if test "x${build_warnings}" != x -a "x$GCC" = xyes
 then
@@ -2020,11 +2043,15 @@ then
     for w in ${build_warnings}; do
 	case $w in
 	-Werr*) WERROR_CFLAGS=-Werror ;;
-	*) # Check that GCC accepts it
+	*)
+	    # Check whether GCC accepts it.
 	    saved_CFLAGS="$CFLAGS"
 	    CFLAGS="$CFLAGS $w"
+	    saved_CXXFLAGS="$CXXFLAGS"
+	    CXXFLAGS="$CXXFLAGS $w"
 	    AC_TRY_COMPILE([],[],WARN_CFLAGS="${WARN_CFLAGS} $w",)
 	    CFLAGS="$saved_CFLAGS"
+	    CXXFLAGS="$saved_CXXFLAGS"
 	esac
     done
     AC_MSG_RESULT(${WARN_CFLAGS} ${WERROR_CFLAGS})
@@ -2032,6 +2059,10 @@ fi
 AC_SUBST(WARN_CFLAGS)
 AC_SUBST(WERROR_CFLAGS)
 
+if test "$enable_build_with_cxx" = "yes"; then
+   AC_LANG_POP([C++])
+fi
+
 # In the Cygwin environment, we need some additional flags.
 AC_CACHE_CHECK([for cygwin], gdb_cv_os_cygwin,
 [AC_EGREP_CPP(^lose$, [