linux-kernel - [PATCH] x86/retpoline: Remove the esp/rsp thunk

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Date:   Mon, 22 Jan 2018 17:09:34 -0500
From:   Waiman Long <longman@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, David Woodhouse <dwmw@...zon.co.uk>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jeff Law <law@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Paul Turner <pjt@...gle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH] x86/retpoline: Remove the esp/rsp thunk

It doesn't make sense to have an indirect call thunk with esp/rsp as
retpoline code won't work correctly with the stack pointer register.
Removing it will help compiler writers to catch error in case such
a thunk call is emitted incorrectly.

Fixes: 76b043848fd2 ("x86/retpoline: Add initial retpoline support")
Suggested-by: Jeff Law <law@...hat.com>
Signed-off-by: Waiman Long <longman@...hat.com>
---
 arch/x86/include/asm/asm-prototypes.h | 1 -
 arch/x86/lib/retpoline.S              | 1 -
 2 files changed, 2 deletions(-)

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index 0927cdc..1908214 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -38,5 +38,4 @@
 INDIRECT_THUNK(si)
 INDIRECT_THUNK(di)
 INDIRECT_THUNK(bp)
-INDIRECT_THUNK(sp)
 #endif /* CONFIG_RETPOLINE */
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index dfb2ba9..c909961 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -36,7 +36,6 @@ GENERATE_THUNK(_ASM_DX)
 GENERATE_THUNK(_ASM_SI)
 GENERATE_THUNK(_ASM_DI)
 GENERATE_THUNK(_ASM_BP)
-GENERATE_THUNK(_ASM_SP)
 #ifdef CONFIG_64BIT
 GENERATE_THUNK(r8)
 GENERATE_THUNK(r9)
-- 
1.8.3.1