Allow glibc to be built with _FORTIFY_SOURCE

Add --enable-fortify-source option.

It is now possible to enable fortification through a configure option.
The level may be given as parameter, if none is provided, the configure
script will determine what is the highest level possible that can be set
considering GCC built-ins availability and set it.
If level is explicitly set to 3, configure checks if the compiler
supports the built-in function necessary for it or raise an error if it
isn't.

If the configure option isn't explicitly enabled, it _FORTIFY_SOURCE is
forcibly undefined (and therefore disabled).

The result of the configure checks are new variables, ${fortify_source}
and ${no_fortify_source} that can be used to appropriately populate
CFLAGS.

A dedicated patch will follow to make use of this variable in Makefiles
when necessary.

Updated NEWS and INSTALL.

Adding dedicated x86_64 variant that enables the configuration.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

1 files changed, 32 insertions, 3 deletions

diff --git a/Makeconfig b/Makeconfig
index 2514db3..77d7fd1 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -543,12 +543,13 @@ endif  # +link
 # ARM, gcc always produces different debugging symbols when invoked with
 # a -O greater than 0 than when invoked with -O0, regardless of anything else
 # we're using to suppress optimizations.  Therefore, we need to explicitly pass
-# -O0 to it through CFLAGS.
+# -O0 to it through CFLAGS. As a result, any fortification needs to be disabled
+# as it needs -O greater than 0.
 # Additionally, the build system will try to -include $(common-objpfx)/config.h
 # when compiling the tests, which will throw an error if some special macros
 # (such as __OPTIMIZE__ and IS_IN_build) aren't defined.  To avoid this, we
 # tell gcc to define IS_IN_build.
-CFLAGS-printers-tests := -O0 -ggdb3 -DIS_IN_build
+CFLAGS-printers-tests := -O0 -ggdb3 -DIS_IN_build $(no-fortify-source)
 
 ifeq (yes,$(build-shared))
 # These indicate whether to link using the built ld.so or the installed one.
@@ -901,6 +902,16 @@ define elide-stack-protector
 $(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-stack-protector))
 endef
 
+# We might want to compile with fortify-source
+ifneq ($(fortify-source),)
++fortify-source=$(fortify-source)
+endif
+
+# Some routine can't be fortified like the ones used by fortify
+define elide-fortify-source
+$(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-fortify-source))
+endef
+
 # The program that makes Emacs-style TAGS files.
 ETAGS	:= etags
 
@@ -961,6 +972,18 @@ endif	# $(+cflags) == ""
 	   $(+stack-protector) -fno-common
 +gcc-nowarn := -w
 
+# We must filter out elf because the early bootstrap of the dynamic loader
+# cannot be fortified. Likewise we exclude dlfcn because it is entangled
+# with the loader. We must filter out csu because early startup, like the
+# loader, cannot be fortified. Lastly debug is the fortification routines
+# themselves and they cannot be fortified.
+do-fortify = $(filter-out elf dlfcn csu debug,$(subdir))
+ifeq ($(do-fortify),$(subdir))
++cflags += $(+fortify-source)
+else
++cflags += $(no-fortify-source)
+endif
+
 # Each sysdeps directory can contain header files that both will be
 # used to compile and will be installed.  Each can also contain an
 # include/ subdirectory, whose header files will be used to compile
@@ -1010,7 +1033,7 @@ module-cppflags = $(if $(filter %.mk.i %.v.i,$(@F)),,$(module-cppflags-real))
 # Note that we can't use -std=* in CPPFLAGS, because it overrides
 # the implicit -lang-asm and breaks cpp behavior for .S files--notably
 # it causes cpp to stop predefining __ASSEMBLER__.
-CPPFLAGS = $(config-extra-cppflags) $(CPPUNDEFS) $(CPPFLAGS-config) \
+CPPFLAGS = $(config-extra-cppflags) $(CPPFLAGS-config) \
 	   $($(subdir)-CPPFLAGS) \
 	   $(+includes) $(defines) $(module-cppflags) \
 	   -include $(..)include/libc-symbols.h $(sysdep-CPPFLAGS) \
@@ -1049,6 +1072,8 @@ object-suffixes :=
 CPPFLAGS-.o = $(pic-default)
 # libc.a must be compiled with -fPIE/-fpie for static PIE.
 CFLAGS-.o = $(filter %frame-pointer,$(+cflags)) $(pie-default)
+CFLAGS-.o += $(call elide-fortify-source,.o,$(routines_no_fortify))
+CFLAGS-.o += $(call elide-fortify-source,_chk.o,$(routines_no_fortify))
 libtype.o := lib%.a
 object-suffixes += .o
 ifeq (yes,$(build-shared))
@@ -1058,6 +1083,8 @@ object-suffixes += .os
 pic-cppflags = -DPIC -DSHARED
 CPPFLAGS-.os = $(pic-cppflags)
 CFLAGS-.os = $(filter %frame-pointer,$(+cflags)) $(pic-ccflag)
+CFLAGS-.os += $(call elide-fortify-source,.os,$(routines_no_fortify))
+CFLAGS-.os += $(call elide-fortify-source,_chk.os,$(routines_no_fortify))
 libtype.os := lib%_pic.a
 # This can be changed by a sysdep makefile
 pic-ccflag = -fPIC
@@ -1077,6 +1104,8 @@ object-suffixes += .op
 CPPFLAGS-.op = -DPROF $(pic-default)
 # libc_p.a must be compiled with -fPIE/-fpie for static PIE.
 CFLAGS-.op = -pg $(pie-default)
+CFLAGS-.op += $(call elide-fortify-source,.op,$(routines_no_fortify))
+CFLAGS-.op += $(call elide-fortify-source,_chk.op,$(routines_no_fortify))
 libtype.op = lib%_p.a
 endif