linux-kernel - [PATCH] x86: Use -mindirect-branch-cs-prefix for RETPOLINE builds

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Message-ID: <20211118185421.GK174703@worktop.programming.kicks-ass.net>
Date:   Thu, 18 Nov 2021 19:54:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, "H.J. Lu" <hjl.tools@...il.com>,
        ndesaulniers@...gle.com
Subject: [PATCH] x86: Use -mindirect-branch-cs-prefix for RETPOLINE builds


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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.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