[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, 2 insertions, 0 deletions

diff --git a/arch/um/sys-x86_64/Makefile b/arch/um/sys-x86_64/Makefile
index f739bea35195..6d3b29c74533 100644
--- a/arch/um/sys-x86_64/Makefile
+++ b/arch/um/sys-x86_64/Makefile
@@ -21,6 +21,8 @@ USER_OBJS := ptrace_user.o sigcontext.o stub_segv.o
 USER_OBJS += user-offsets.s
 extra-y += user-offsets.s
 
+CFLAGS_stub_segv.o := $(CFLAGS_NO_HARDENING)
+
 extra-$(CONFIG_MODE_TT) += unmap.o
 
 include arch/um/scripts/Makefile.rules