From: Andi Kleen <a...@linux.intel.com> The speculative jump trampoline has to contain unreachable code. objtool keeps complaining
arch/x86/lib/retpoline.o: warning: objtool: __x86.indirect_thunk()+0x8: unreachable instruction I tried to fix it here by adding ASM_UNREACHABLE annotation (after supporting them for pure assembler), but it still complains. Seems like a objtool bug? So it doesn't actually fix the warning oyet. Of course it's just a warning so the kernel will still work fine. Perhaps Josh can figure it out Cc: jpoim...@redhat.com Not-Signed-off-by: Andi Kleen <a...@linux.intel.com> --- arch/x86/lib/retpoline.S | 3 +++ include/linux/compiler.h | 10 +++++++++- 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index cb40781adbfe..f4ed556a90ee 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -11,6 +11,7 @@ */ #include <linux/linkage.h> +#include <linux/compiler.h> #include <asm/dwarf2.h> #include <asm/export.h> @@ -21,7 +22,9 @@ ENTRY(__x86.indirect_thunk) call retpoline_call_target 2: lfence /* stop speculation */ + ASM_UNREACHABLE jmp 2b + ASM_UNREACHABLE retpoline_call_target: #ifdef CONFIG_64BIT lea 8(%rsp), %rsp diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 52e611ab9a6c..cfba91acc79a 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -269,7 +269,15 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s #endif /* __KERNEL__ */ -#endif /* __ASSEMBLY__ */ +#else /* __ASSEMBLY__ */ + +#define ASM_UNREACHABLE \ + 999: \ + .pushsection .discard.unreachable; \ + .long 999b - .; \ + .popsection + +#endif /* !__ASSEMBLY__ */ /* Compile time object size, -1 for unknown */ #ifndef __compiletime_object_size -- 2.14.3