[PATCH] uml: fix compilation and execution with hardened GCC

To make some half-assembly stubs compile, disable various "hardened" GCC
features:

*) we can't make it build PIC code as we need %ebx to do syscalls and GCC
   wants it free for PIC

*) we can't leave stack protection as the stub is moved (not relocated!) in
   memory so the RIP-relative access to the canary tries reading from an
   unmapped address and causes a segfault, since we move the stub of various
   megabytes (the exact amount will be decided at runtime) away from the
   link-time address.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/um/Makefile b/arch/um/Makefile
index 930e00612a22..bed604af6c6f 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -118,6 +118,10 @@ prepare: $(ARCH_DIR)/include/kern_constants.h
 LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
 LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib
 
+CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
+        $(call cc-option, -fno-stack-protector,) \
+        $(call cc-option, -fno-stack-protector-all,)
+
 CPP_MODE-$(CONFIG_MODE_TT) := -DMODE_TT
 CONFIG_KERNEL_STACK_ORDER ?= 2
 STACK_SIZE := $(shell echo $$[ 4096 * (1 << $(CONFIG_KERNEL_STACK_ORDER)) ] )
@@ -227,4 +231,4 @@ $(ARCH_DIR)/include/kern_constants.h: $(objtree)/$(ARCH_DIR)/include
         @echo '  SYMLINK $@'
         $(Q)ln -sf ../../../include/asm-um/asm-offsets.h $@
 
-export SUBARCH USER_CFLAGS OS
+export SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING OS