Use -Werror by default, add --disable-werror.

As discussed starting at
<https://sourceware.org/ml/libc-alpha/2014-11/msg00323.html>, this
patch makes the glibc build use -Werror by default to avoid
accidentally adding new warnings to the build.  The configure option
--disable-werror can be used to disable this.

-Wno-error=undef is temporarily used because the build isn't clean
regarding -Wundef warnings.  The idea is that once the remaining
-Wundef warnings have been cleaned up (in at least one configuration),
-Wno-error=undef will be removed.

I get a clean build and test on x86_64 (GCC 4.9 branch) with this
patch.  The expectation is that this may well break the build for some
other configurations, and people seeing such breakage should make
appropriate fixes to fix or suppress the warnings for their
configurations.  In some cases that may involve using pragmas as the
right fix (I think that will be right for the -Wno-inline issue for
MIPS I referred to in
<https://sourceware.org/ml/libc-alpha/2012-11/msg00798.html>, for
example), in some cases -Wno-error in sysdeps makefiles (__restore_rt
in MIPS sigaction, for example), in some cases substantive fixes for
the warnings.

Note that if, with a view to listing all the warnings then fixing them
all, you just look for "warning:" in output from building and testing
with --disable-werror, you'll see lots of warnings from the linker
about functions such as tmpnam.  Those warnings can be ignored - only
compiler warnings are relevant to -Werror, not linker warnings.

	* configure.ac (--disable-werror): New configure option.
	(enable_werror): New AC_SUBST.
	* configure: Regenerated.
	* config.make.in (enable-werror): New variable.
	* Makeconfig [$(enable-werror) = yes] (+gccwarn): Add -Werror
	-Wno-error=undef.
	(+gccwarn-c): Do not use -Werror=implicit-function-declaration.
	* manual/install.texi (Configuring and compiling): Document
	--disable-werror.
	* INSTALL: Regenerated.
	* debug/Makefile (CFLAGS-tst-chk1.c): Add -Wno-error.
	(CFLAGS-tst-chk2.c): Likewise.
	(CFLAGS-tst-chk3.c): Likewise.
	(CFLAGS-tst-chk4.cc): Likewise.
	(CFLAGS-tst-chk5.cc): Likewise.
	(CFLAGS-tst-chk6.cc): Likewise.
	(CFLAGS-tst-lfschk1.c): Likewise.
	(CFLAGS-tst-lfschk2.c): Likewise.
	(CFLAGS-tst-lfschk3.c): Likewise.
	(CFLAGS-tst-lfschk4.cc): Likewise.
	(CFLAGS-tst-lfschk5.cc): Likewise.
	(CFLAGS-tst-lfschk6.cc): Likewise.

9 files changed, 79 insertions, 14 deletions

diff --git a/ChangeLog b/ChangeLog
index 1014ba3dff..f8652231de 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,28 @@
 2014-12-10  Joseph Myers  <joseph@codesourcery.com>
 
+	* configure.ac (--disable-werror): New configure option.
+	(enable_werror): New AC_SUBST.
+	* configure: Regenerated.
+	* config.make.in (enable-werror): New variable.
+	* Makeconfig [$(enable-werror) = yes] (+gccwarn): Add -Werror
+	-Wno-error=undef.
+	(+gccwarn-c): Do not use -Werror=implicit-function-declaration.
+	* manual/install.texi (Configuring and compiling): Document
+	--disable-werror.
+	* INSTALL: Regenerated.
+	* debug/Makefile (CFLAGS-tst-chk1.c): Add -Wno-error.
+	(CFLAGS-tst-chk2.c): Likewise.
+	(CFLAGS-tst-chk3.c): Likewise.
+	(CFLAGS-tst-chk4.cc): Likewise.
+	(CFLAGS-tst-chk5.cc): Likewise.
+	(CFLAGS-tst-chk6.cc): Likewise.
+	(CFLAGS-tst-lfschk1.c): Likewise.
+	(CFLAGS-tst-lfschk2.c): Likewise.
+	(CFLAGS-tst-lfschk3.c): Likewise.
+	(CFLAGS-tst-lfschk4.cc): Likewise.
+	(CFLAGS-tst-lfschk5.cc): Likewise.
+	(CFLAGS-tst-lfschk6.cc): Likewise.
+
 	* stdio-common/tst-printfsz.c: Include <libc-internal.h>.
 	(main): Disable -Wdeprecated-declarations around calls to
 	register_printf_function.
diff --git a/INSTALL b/INSTALL
index dac6178bac..dd5c34aadb 100644
--- a/INSTALL
+++ b/INSTALL
@@ -143,6 +143,13 @@ will be used, and CFLAGS sets optimization options for the compiler.
      additional security risks to the system and you should enable it
      only if you understand and accept those risks.
 
+`--disable-werror'
+     By default, the GNU C Library is built with `-Werror'.  If you wish
+     to build without this option (for example, if building with a newer
+     version of GCC than this version of the GNU C Library was tested
+     with, so new warnings cause the build with `-Werror' to fail), you
+     can configure with `--disable-werror'.
+
 `--build=BUILD-SYSTEM'
 `--host=HOST-SYSTEM'
      These options are for cross-compiling.  If you specify both
diff --git a/Makeconfig b/Makeconfig
index bbf546072c..15553681a0 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -717,7 +717,10 @@ else
 +gccwarn := -Wall -Wwrite-strings -Winline
 endif
 +gccwarn += -Wundef
-+gccwarn-c = -Wstrict-prototypes -Werror=implicit-function-declaration
+ifeq ($(enable-werror),yes)
++gccwarn += -Werror -Wno-error=undef
+endif
++gccwarn-c = -Wstrict-prototypes
 
 # We do not depend on the address of constants in different files to be
 # actually different, so allow the compiler to merge them all.
diff --git a/NEWS b/NEWS
index 1b08d40a68..2cc4a611dc 100644
--- a/NEWS
+++ b/NEWS
@@ -26,6 +26,9 @@ Version 2.21
   C Library is GCC 4.6.  Older GCC versions, and non-GNU compilers, can
   still be used to compile programs using the GNU C Library.
 
+* The GNU C Library is now built with -Werror by default.  This can be
+  disabled by configuring with --disable-werror.
+
 * New locales: tu_IN, bh_IN, raj_IN, ce_RU.
 
 * The obsolete sigvec function has been removed.  This was the original
diff --git a/config.make.in b/config.make.in
index 4a781fdc4a..ad4dd30607 100644
--- a/config.make.in
+++ b/config.make.in
@@ -45,6 +45,7 @@ sysheaders = @sysheaders@
 sysincludes = @SYSINCLUDES@
 c++-sysincludes = @CXX_SYSINCLUDES@
 all-warnings = @all_warnings@
+enable-werror = @enable_werror@
 
 have-z-combreloc = @libc_cv_z_combreloc@
 have-z-execstack = @libc_cv_z_execstack@
diff --git a/configure b/configure
index 0cb54ec363..b1fda3867a 100755
--- a/configure
+++ b/configure
@@ -668,6 +668,7 @@ build_pt_chown
 build_nscd
 link_obsolete_rpc
 libc_cv_nss_crypt
+enable_werror
 all_warnings
 force_install
 bindnow
@@ -767,6 +768,7 @@ enable_force_install
 enable_maintainer_mode
 enable_kernel
 enable_all_warnings
+enable_werror
 enable_multi_arch
 enable_nss_crypt
 enable_obsolete_rpc
@@ -1428,6 +1430,7 @@ Optional Features:
   --enable-kernel=VERSION compile for compatibility with kernel not older than
                           VERSION
   --enable-all-warnings   enable all useful warnings gcc can issue
+  --disable-werror        do not build with -Werror
   --enable-multi-arch     enable single DSO with optimizations for multiple
                           architectures
   --enable-nss-crypt      enable libcrypt to use nss
@@ -3565,6 +3568,15 @@ fi
 
 
 
+# Check whether --enable-werror was given.
+if test "${enable_werror+set}" = set; then :
+  enableval=$enable_werror; enable_werror=$enableval
+else
+  enable_werror=yes
+fi
+
+
+
 # Check whether --enable-multi-arch was given.
 if test "${enable_multi_arch+set}" = set; then :
   enableval=$enable_multi_arch; multi_arch=$enableval
diff --git a/configure.ac b/configure.ac
index b2c4b1fab8..784e360382 100644
--- a/configure.ac
+++ b/configure.ac
@@ -253,6 +253,13 @@ AC_ARG_ENABLE([all-warnings],
 	      [])
 AC_SUBST(all_warnings)
 
+AC_ARG_ENABLE([werror],
+	      AC_HELP_STRING([--disable-werror],
+			     [do not build with -Werror]),
+	      [enable_werror=$enableval],
+	      [enable_werror=yes])
+AC_SUBST(enable_werror)
+
 AC_ARG_ENABLE([multi-arch],
 	      AC_HELP_STRING([--enable-multi-arch],
 			     [enable single DSO with optimizations for multiple architectures]),
diff --git a/debug/Makefile b/debug/Makefile
index 3ddcd1e1c3..96c21d5d40 100644
--- a/debug/Makefile
+++ b/debug/Makefile
@@ -96,19 +96,21 @@ CFLAGS-tst-longjmp_chk3.c = -fexceptions -fasynchronous-unwind-tables
 CPPFLAGS-tst-longjmp_chk3.c = -D_FORTIFY_SOURCE=1
 
 # We know these tests have problems with format strings, this is what
-# we are testing.  Disable that warning.
-CFLAGS-tst-chk1.c = -Wno-format
-CFLAGS-tst-chk2.c = -Wno-format
-CFLAGS-tst-chk3.c = -Wno-format
-CFLAGS-tst-chk4.cc = -Wno-format
-CFLAGS-tst-chk5.cc = -Wno-format
-CFLAGS-tst-chk6.cc = -Wno-format
-CFLAGS-tst-lfschk1.c = -Wno-format
-CFLAGS-tst-lfschk2.c = -Wno-format
-CFLAGS-tst-lfschk3.c = -Wno-format
-CFLAGS-tst-lfschk4.cc = -Wno-format
-CFLAGS-tst-lfschk5.cc = -Wno-format
-CFLAGS-tst-lfschk6.cc = -Wno-format
+# we are testing.  Disable that warning.  They also generate warnings
+# from warning attributes, which cannot be disabled via pragmas, so
+# require -Wno-error to be used.
+CFLAGS-tst-chk1.c = -Wno-format -Wno-error
+CFLAGS-tst-chk2.c = -Wno-format -Wno-error
+CFLAGS-tst-chk3.c = -Wno-format -Wno-error
+CFLAGS-tst-chk4.cc = -Wno-format -Wno-error
+CFLAGS-tst-chk5.cc = -Wno-format -Wno-error
+CFLAGS-tst-chk6.cc = -Wno-format -Wno-error
+CFLAGS-tst-lfschk1.c = -Wno-format -Wno-error
+CFLAGS-tst-lfschk2.c = -Wno-format -Wno-error
+CFLAGS-tst-lfschk3.c = -Wno-format -Wno-error
+CFLAGS-tst-lfschk4.cc = -Wno-format -Wno-error
+CFLAGS-tst-lfschk5.cc = -Wno-format -Wno-error
+CFLAGS-tst-lfschk6.cc = -Wno-format -Wno-error
 LDLIBS-tst-chk4 = -lstdc++
 LDLIBS-tst-chk5 = -lstdc++
 LDLIBS-tst-chk6 = -lstdc++
diff --git a/manual/install.texi b/manual/install.texi
index 1eafb6ec32..35467b1b16 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -174,6 +174,13 @@ setuid and owned by @code{root}.  The use of @file{pt_chown} introduces
 additional security risks to the system and you should enable it only if
 you understand and accept those risks.
 
+@item --disable-werror
+By default, @theglibc{} is built with @option{-Werror}.  If you wish
+to build without this option (for example, if building with a newer
+version of GCC than this version of @theglibc{} was tested with, so
+new warnings cause the build with @option{-Werror} to fail), you can
+configure with @option{--disable-werror}.
+
 @item --build=@var{build-system}
 @itemx --host=@var{host-system}
 These options are for cross-compiling.  If you specify both options and