x86/ubsan: Don't perform alignment checking on supporting compilers

GCC 5 introduced -fsanitize=alignment which is enabled by default by
CONFIG_UBSAN.  This trips a load of wont-fix cases in the ACPI tables and the
hypercall page and stubs writing logic.

It also causes the native Xen boot to crash before the console is set up, for
an as-yet unidentified reason (most likley a wont-fix case earlier on boot).

Disable alignment sanitisation on compilers which would try using it.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/Rules.mk b/xen/Rules.mk
index a151b3f625bc5500c8c2b5fd40e87e70ff1a1c30..3090ea78288f5962204c1c537435b0d95c944d04 100644 (file)
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -41,6 +41,9 @@ ALL_OBJS-y               += $(BASEDIR)/xsm/built_in.o
 ALL_OBJS-y               += $(BASEDIR)/arch/$(TARGET_ARCH)/built_in.o
 ALL_OBJS-$(CONFIG_CRYPTO)   += $(BASEDIR)/crypto/built_in.o
 
+# Initialise some variables
+CFLAGS_UBSAN :=
+
 ifeq ($(CONFIG_DEBUG),y)
 CFLAGS += -O1
 else
@@ -138,7 +141,10 @@ $(filter-out %.init.o $(nocov-y),$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS += $(
 endif
 
 ifeq ($(CONFIG_UBSAN),y)
-$(filter-out %.init.o $(noubsan-y),$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS += -fsanitize=undefined
+CFLAGS_UBSAN += -fsanitize=undefined
+# Any -fno-sanitize= options need to come after any -fsanitize= options
+$(filter-out %.init.o $(noubsan-y),$(obj-y) $(obj-bin-y) $(extra-y)): \
+CFLAGS += $(filter-out -fno-%,$(CFLAGS_UBSAN)) $(filter -fno-%,$(CFLAGS_UBSAN))
 endif
 
 ifeq ($(CONFIG_LTO),y)

diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
index babc0edbcdfbb9eb480faea3743c1d038a0a08e4..52e93afb4892269e459e48573fbec24033775336 100644 (file)
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -57,6 +57,14 @@ endif
 $(call cc-option-add,CFLAGS-stack-boundary,CC,-mpreferred-stack-boundary=3)
 CFLAGS += $(CFLAGS-stack-boundary)
 
+ifeq ($(CONFIG_UBSAN),y)
+# Don't enable alignment sanitisation.  x86 has efficient unaligned accesses,
+# and various things (ACPI tables, hypercall pages, stubs, etc) are wont-fix.
+# It also causes an as-yet-unidentified crash on native boot before the
+# console starts.
+$(call cc-option-add,CFLAGS_UBSAN,CC,-fno-sanitize=alignment)
+endif
+
 # Set up the assembler include path properly for older toolchains.
 CFLAGS += -Wa,-I$(BASEDIR)/include