[PATCH] x86/retpoline: Switch thunk names to match final GCC patches

[PATCH] x86/retpoline: Switch thunk names to match final GCC patches

[David Woodhouse]

At the last minute, they were switched from __x86_indirect_thunk_rax to
__x86_indirect_thunk_ax without the 'r' or 'e' on the register name.
Except for the _r[89..] versions, obviously.

This is not entirely an improvement, IMO.

Reluctantly-signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
I think we *shouldn't* do this. Uros said we could look at it and make
a decision, and GCC would implement what we decide. Up to Linus.

I'm sending this because I've built the compiler with the proposed
changes and tested it, and it's quarter past Monday and I'm done. Not
because I really want it.

 arch/x86/entry/entry_64.S             |  2 +-
 arch/x86/include/asm/asm-prototypes.h | 24 ++++++++++----------
 arch/x86/lib/retpoline.S              | 41 +++++++++++++++++------------------
 3 files changed, 32 insertions(+), 35 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 59874bc..e393163 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -269,7 +269,7 @@ entry_SYSCALL_64_fastpath:
 	 */
 #ifdef CONFIG_RETPOLINE
 	movq	sys_call_table(, %rax, 8), %rax
-	call	__x86_indirect_thunk_rax
+	call	__x86_indirect_thunk_ax
 #else
 	call	*sys_call_table(, %rax, 8)
 #endif
diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index 0927cdc..df80478 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -18,19 +18,7 @@ extern void cmpxchg8b_emu(void);
 #endif
 
 #ifdef CONFIG_RETPOLINE
-#ifdef CONFIG_X86_32
-#define INDIRECT_THUNK(reg) extern asmlinkage void __x86_indirect_thunk_e ## reg(void);
-#else
-#define INDIRECT_THUNK(reg) extern asmlinkage void __x86_indirect_thunk_r ## reg(void);
-INDIRECT_THUNK(8)
-INDIRECT_THUNK(9)
-INDIRECT_THUNK(10)
-INDIRECT_THUNK(11)
-INDIRECT_THUNK(12)
-INDIRECT_THUNK(13)
-INDIRECT_THUNK(14)
-INDIRECT_THUNK(15)
-#endif
+#define INDIRECT_THUNK(reg) extern asmlinkage void __x86_indirect_thunk_ ## reg(void);
 INDIRECT_THUNK(ax)
 INDIRECT_THUNK(bx)
 INDIRECT_THUNK(cx)
@@ -39,4 +27,14 @@ INDIRECT_THUNK(si)
 INDIRECT_THUNK(di)
 INDIRECT_THUNK(bp)
 INDIRECT_THUNK(sp)
+#ifdef CONFIG_64BIT
+INDIRECT_THUNK(r8)
+INDIRECT_THUNK(r9)
+INDIRECT_THUNK(r10)
+INDIRECT_THUNK(r11)
+INDIRECT_THUNK(r12)
+INDIRECT_THUNK(r13)
+INDIRECT_THUNK(r14)
+INDIRECT_THUNK(r15)
+#endif /* CONFIG_64BIT */
 #endif /* CONFIG_RETPOLINE */
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index cb45c6c..7da2c90 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -8,14 +8,14 @@
 #include <asm/export.h>
 #include <asm/nospec-branch.h>
 
-.macro THUNK reg
-	.section .text.__x86.indirect_thunk.\reg
+.macro THUNK reg suffix
+	.section .text.__x86.indirect_thunk.\suffix
 
-ENTRY(__x86_indirect_thunk_\reg)
+ENTRY(__x86_indirect_thunk_\suffix)
 	CFI_STARTPROC
 	JMP_NOSPEC %\reg
 	CFI_ENDPROC
-ENDPROC(__x86_indirect_thunk_\reg)
+ENDPROC(__x86_indirect_thunk_\suffix)
 .endm
 
 /*
@@ -26,23 +26,22 @@ ENDPROC(__x86_indirect_thunk_\reg)
  * the simple and nasty way...
  */
 #define EXPORT_THUNK(reg) EXPORT_SYMBOL(__x86_indirect_thunk_ ## reg)
-#define GENERATE_THUNK(reg) THUNK reg ; EXPORT_THUNK(reg)
+#define GENERATE_THUNK(reg, suffix) THUNK reg suffix; EXPORT_THUNK(suffix)
 
-GENERATE_THUNK(_ASM_AX)
-GENERATE_THUNK(_ASM_BX)
-GENERATE_THUNK(_ASM_CX)
-GENERATE_THUNK(_ASM_DX)
-GENERATE_THUNK(_ASM_SI)
-GENERATE_THUNK(_ASM_DI)
-GENERATE_THUNK(_ASM_BP)
-GENERATE_THUNK(_ASM_SP)
+GENERATE_THUNK(_ASM_AX, ax)
+GENERATE_THUNK(_ASM_BX, bx)
+GENERATE_THUNK(_ASM_CX, cx)
+GENERATE_THUNK(_ASM_DX, dx)
+GENERATE_THUNK(_ASM_SI, si)
+GENERATE_THUNK(_ASM_DI, di)
+GENERATE_THUNK(_ASM_BP, bp)
 #ifdef CONFIG_64BIT
-GENERATE_THUNK(r8)
-GENERATE_THUNK(r9)
-GENERATE_THUNK(r10)
-GENERATE_THUNK(r11)
-GENERATE_THUNK(r12)
-GENERATE_THUNK(r13)
-GENERATE_THUNK(r14)
-GENERATE_THUNK(r15)
+GENERATE_THUNK(r8, r8)
+GENERATE_THUNK(r9, r9)
+GENERATE_THUNK(r10, r10)
+GENERATE_THUNK(r11, r11)
+GENERATE_THUNK(r12, r12)
+GENERATE_THUNK(r13, r13)
+GENERATE_THUNK(r14, r14)
+GENERATE_THUNK(r15, r15)
 #endif
-- 
2.7.4

Re: [PATCH] x86/retpoline: Switch thunk names to match final GCC patches

[Linus Torvalds]

On Sun, Jan 14, 2018 at 3:23 PM, David Woodhouse <dwmw@amazon.co.uk> wrote:
> I think we *shouldn't* do this. Uros said we could look at it and make
> a decision, and GCC would implement what we decide. Up to Linus.

Regardless of whether we end up having to do this, I'm not doing rc8
with it, and let's hope we can just skip it entirely.

It seems silly to have the 'r' for the r8-r15 case, but not the legacy
registers.

                  Linus