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: 76b0438 ("x86/retpoline: Add initial retpoline support")
Suggested-by: Jeff Law <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: David Woodhouse <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Paul Turner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: Waiman-Long

arch/x86/include/asm/asm-prototypes.h

@@ -38,5 +38,4 @@ INDIRECT_THUNK(dx)
 INDIRECT_THUNK(si)
 INDIRECT_THUNK(di)
 INDIRECT_THUNK(bp)
-INDIRECT_THUNK(sp)
 #endif /* CONFIG_RETPOLINE */

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)