Build libc-start with stack protector for SHARED

This does not change the emitted code since __libc_start_main does not
return, but is important for formal flags compliance.

This also cleans up the cosmetic inconsistency in the stack protector
flags in csu, especially the incorrect value of STACK_PROTECTOR_LEVEL.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

diff --git a/Makeconfig b/Makeconfig
index 0a4811b5e5d7f3e493ba14007f6ce2017caffb89..01f8638c2e12bd7a82ac90869d909e7438e63177 100644 (file)
--- a/Makeconfig
+++ b/Makeconfig
@@ -856,6 +856,14 @@ ifneq ($(stack-protector),)
 +stack-protector=$(stack-protector)
 endif
 
+# Some routines are unsafe to build with stack-protection since they're called
+# before the stack check guard is set up.  Provide a way to disable stack
+# protector.  The first argument is the extension (.o, .os, .oS) and the second
+# is a list of routines that this path should be applied to.
+define elide-stack-protector
+$(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-stack-protector))
+endef
+
 # This is the program that generates makefile dependencies from C source files.
 # The -MP flag tells GCC >= 3.2 (which we now require) to produce dummy
 # targets for headers so that removed headers don't break the build.

diff --git a/csu/Makefile b/csu/Makefile
index e587434be86c8bcb66c9166a6780c8a2a7e71a58..3054329cea4a276d5e2312e6b5d659192ff06423 100644 (file)
--- a/csu/Makefile
+++ b/csu/Makefile
@@ -45,18 +45,20 @@ install-lib = $(start-installed-name) g$(start-installed-name) $(csu-dummies)
 # code is compiled with special flags.
 tests =
 
-CFLAGS-.o += $(no-stack-protector)
-CFLAGS-.op += $(no-stack-protector)
-CFLAGS-.os += $(no-stack-protector)
-
-# Dummy object not actually used for anything.  It is linked into
-# crt1.o nevertheless, which in turn is statically linked into
+# static-reloc.os is a dummy object not actually used for anything.  It is
+# linked into crt1.o nevertheless, which in turn is statically linked into
 # applications, so that build flags matter.
 # See <https://sourceware.org/ml/libc-alpha/2018-07/msg00101.html>.
-# NB: Using $(stack-protector) in this way causes a wrong definition
-# STACK_PROTECTOR_LEVEL due to the preceding $(no-stack-protector),
-# but it does not matter for this source file.
-CFLAGS-static-reloc.os += $(stack-protector)
+#
+# libc-start.os is safe to be built with stack protector since
+# __libc_start_main is called after stack canary setup is done.
+ssp-safe.os = static-reloc libc-start
+
+CFLAGS-.o += $(call elide-stack-protector,.o,$(routines))
+CFLAGS-.op += $(call elide-stack-protector,.op,$(routines))
+CFLAGS-.oS += $(call elide-stack-protector,.oS,$(routines))
+CFLAGS-.os += $(call elide-stack-protector,.os,$(filter-out \
+                                                $(ssp-safe.os),$(routines)))
 
 ifeq (yes,$(build-shared))
 extra-objs += S$(start-installed-name) gmon-start.os

diff --git a/elf/Makefile b/elf/Makefile
index ba4689a7fa8a10fd1e0ef068c71fd6e075e383ee..3b8e13e066e087c5e57e3797aaf15681529d2726 100644 (file)
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -83,10 +83,6 @@ endif
 # Also compile all routines in the static library that are elided from
 # the shared libc because they are in libc.a in the same way.
 
-define elide-stack-protector
-$(if $(filter $(@F),$(patsubst %,%$(1),$(2))), $(no-stack-protector))
-endef
-
 CFLAGS-.o += $(call elide-stack-protector,.o,$(elide-routines.os))
 CFLAGS-.op += $(call elide-stack-protector,.op,$(elide-routines.os))
 CFLAGS-.os += $(call elide-stack-protector,.os,$(all-rtld-routines))