From: Andi Kleen <[email protected]> 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: [email protected] Not-Signed-off-by: Andi Kleen <[email protected]> Not-Signed-off-by: David Woodhouse <[email protected]> --- arch/x86/lib/retpoline.S | 5 +++++ include/linux/compiler.h | 10 +++++++++- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index bbdda5cc136e..8112feaea6ff 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -2,6 +2,7 @@ #include <linux/stringify.h> #include <linux/linkage.h> +#include <linux/compiler.h> #include <asm/dwarf2.h> #include <asm/cpufeatures.h> #include <asm/alternative-asm.h> @@ -14,7 +15,9 @@ ENTRY(__x86.indirect_thunk.\reg) ALTERNATIVE "call 2f", __stringify(jmp *%\reg), X86_BUG_NO_RETPOLINE 1: lfence + ASM_UNREACHABLE jmp 1b + ASM_UNREACHABLE 2: mov %\reg, (%\sp) ret @@ -40,7 +43,9 @@ ENTRY(__x86.indirect_thunk) ALTERNATIVE "call 2f", "ret", X86_BUG_NO_RETPOLINE 1: lfence + ASM_UNREACHABLE jmp 1b + ASM_UNREACHABLE 2: lea 4(%esp), %esp ret 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
