From 9412486707f8f1ca2eb31c2ef330c5e39c0a2f30 Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Fri, 18 Feb 2022 15:34:15 +0100 Subject: [PATCH] x86/clang: add retpoline support MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 in a register always on amd64, so there's no need for any equivalent mindirect-branch-register parameter. Reported-by: Andrew Cooper Signed-off-by: Roger Pau Monné Acked-by: Andrew Cooper --- xen/arch/x86/Kconfig | 3 ++- xen/arch/x86/arch.mk | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig index fe89fa7274..1465874097 100644 --- a/xen/arch/x86/Kconfig +++ b/xen/arch/x86/Kconfig @@ -33,7 +33,8 @@ config ARCH_DEFCONFIG default "arch/x86/configs/x86_64_defconfig" config CC_HAS_INDIRECT_THUNK - def_bool $(cc-option,-mindirect-branch-register) + def_bool $(cc-option,-mindirect-branch-register) || \ + $(cc-option,-mretpoline-external-thunk) config INDIRECT_THUNK def_bool y diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk index 15d0cbe487..edfc043dbb 100644 --- a/xen/arch/x86/arch.mk +++ b/xen/arch/x86/arch.mk @@ -47,6 +47,9 @@ ifeq ($(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 -- 2.39.5