Re: [PATCH] x86: Use -mindirect-branch-cs-prefix for RETPOLINE builds
From: Nick Desaulniers <ndesaulniers@google.com>
Date: 2021-11-18 22:08:20
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lkml, llvm
On Thu, Nov 18, 2021 at 10:54 AM Peter Zijlstra [off-list ref] wrote:
In order to further enable commit:
bbe2df3f6b6d ("x86/alternative: Try inline spectre_v2=retpoline,amd")
add the new GCC flag -mindirect-branch-cs-prefix:
https://gcc.gnu.org/g:2196a681d7810ad8b227bf983f38ba716620545e
to RETPOLINE=y builds. This should allow fully inlining retpoline,amd
for GCC builds.Do you mind adding the following link tags: Link: https://gcc.gnu.org/g:2196a681d7810ad8b227bf983f38ba716620545e Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102952 Link: https://bugs.llvm.org/show_bug.cgi?id=52323 If the feature would be helpful to implement in Clang, would you mind keeping the cc-option, but moving the check outside of the `ifdef CONFIG_CC_IS_GCC` block? That way, we don't need to revisit the Makefile? (Tangential: I wonder why RETPOLINE_CFLAGS aren't defined in arch/x86/Makefile; they seem to be x86 specific at the moment). With the above link tags, and with or without moving this outside the gcc-specific guard: Acked-by: Nick Desaulniers <ndesaulniers@google.com>
quoted hunk
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- Makefile | 1 + 1 file changed, 1 insertion(+)diff --git a/Makefile b/Makefile index 9e12c14ea0fb..5fd5b5f091ae 100644 --- a/Makefile +++ b/Makefile@@ -690,6 +690,7 @@ endif ifdef CONFIG_CC_IS_GCC RETPOLINE_CFLAGS := $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register) +RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch-cs-prefix) RETPOLINE_VDSO_CFLAGS := $(call cc-option,-mindirect-branch=thunk-inline -mindirect-branch-register) endif ifdef CONFIG_CC_IS_CLANG
-- Thanks, ~Nick Desaulniers