Messages in this thread Patch in this message | | | Date | Tue, 22 Nov 2022 09:35:17 +0100 | From | Peter Zijlstra <> | Subject | Re: objtool warning for next-20221118 |
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On Mon, Nov 21, 2022 at 09:16:05PM -0800, Josh Poimboeuf wrote:
> It's complaining about an unreachable instruction after a call to > arch_cpu_idle_dead(). In this case objtool detects the fact > arch_cpu_idle_dead() doesn't return due to its call to the > non-CONFIG_SMP version of play_dead(). But GCC has no way of detecting > that because the caller is in another translation unit. > > As far as I can tell, that function should never return. Though it > seems to have some dubious semantics (see xen_pv_play_dead() for > example, which *does* seem to return?). I'm thinking it would be an > improvement to enforce that noreturn behavior across all arches and > platforms, sprinkling __noreturn and BUG() on arch_cpu_idle_dead() and > maybe some of it callees, where needed. > > Peter, what do you think? I could attempt a patch.
I'm thinking the Xen case makes all this really rather difficult :/
While normally a CPU is brought up through a trampoline, Xen seems to have implemented it by simply returning from play_dead(), and afaict that is actually a valid way to go about doing it.
Perhaps the best way would be to stick a REACHABLE annotation in arch_cpu_idle_dead() or something?
--- diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index c21b7347a26d..0354be027eb0 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -712,6 +712,7 @@ void arch_cpu_idle_enter(void) void arch_cpu_idle_dead(void) { play_dead(); + asm(ASM_REACHABLE); } /*
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