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[PATCH v3 2/3] x86/clang: add retpoline support
- To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Date: Fri, 18 Feb 2022 15:34:15 +0100
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Fri, 18 Feb 2022 14:34:54 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Detect whether the compiler supports clang retpoline option and enable
by default if available, just like it's done for gcc.
Note clang already disables jump tables when retpoline is enabled, so
there's no need to also pass the fno-jump-tables parameter. Also clang
already passes the return address on a register always on amd64, so
there's no need for any equivalent mindirect-branch-register
parameter.
Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
xen/arch/x86/Kconfig | 4 +++-
xen/arch/x86/arch.mk | 3 +++
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index a1a90da4fc..f8dca4dc85 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -33,7 +33,9 @@ config ARCH_DEFCONFIG
default "arch/x86/configs/x86_64_defconfig"
config CC_INDIRECT_THUNK
- def_bool $(cc-option,-mindirect-branch-register)
+ def_bool $(cc-option,-mindirect-branch-register) || \
+ $(cc-option,-mretpoline-external-thunk)
+
config INDIRECT_THUNK
def_bool y
diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
index 6388b1d93f..066d749ba0 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -47,6 +47,9 @@ ifeq ($(CONFIG_INDIRECT_THUNK),y)
CFLAGS-$(CONFIG_CC_IS_GCC) += -mindirect-branch=thunk-extern
CFLAGS-$(CONFIG_CC_IS_GCC) += -mindirect-branch-register
CFLAGS-$(CONFIG_CC_IS_GCC) += -fno-jump-tables
+
+# Enable clang retpoline support if available.
+CFLAGS-$(CONFIG_CC_IS_CLANG) += -mretpoline-external-thunk
endif
# If supported by the compiler, reduce stack alignment to 8 bytes. But allow
--
2.34.1
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