[Xen-changelog] [xen staging] x86/ubsan: Don't perform alignment checking on supporting compilers

[patchbot@xxxxxxx]

commit 3b6eff372806cc71b30acf5159febd21fa2c1cc0
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jun 24 10:43:34 2019 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Jul 31 14:37:56 2019 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/Rules.mk          | 8 +++++++-
 xen/arch/x86/Rules.mk | 8 ++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index a151b3f625..3090ea7828 100644
--- 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 babc0edbcd..52e93afb48 100644
--- 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
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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