linux-kernel - Re: [PATCH 3/4] x86,objtool: Mark cpu_startup_entry() _

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Date:   Mon, 11 Apr 2022 13:32:37 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        rick.p.edgecombe@...el.com
Subject: Re: [PATCH 3/4] x86,objtool: Mark cpu_startup_entry() __noreturn

On Fri, Apr 08, 2022 at 11:45:55AM +0200, Peter Zijlstra wrote:
> GCC-8 isn't clever enough to figure out that cpu_start_entry() is a
> noreturn while objtool is. This results in code after the call in
> start_secondary(). Give GCC a hand so that they all agree on things.
> 
>   vmlinux.o: warning: objtool: start_secondary()+0x10e: unreachable
> 
> Reported-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/cpu.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -167,7 +167,7 @@ static inline int suspend_disable_second
>  static inline void suspend_enable_secondary_cpus(void) { }
>  #endif /* !CONFIG_PM_SLEEP_SMP */
>  
> -void cpu_startup_entry(enum cpuhp_state state);
> +void __noreturn cpu_startup_entry(enum cpuhp_state state);
>  
>  void cpu_idle_poll_ctrl(bool enable);

I just ran into this:

  init/main.o: warning: objtool: rest_init() falls through to next function kernel_init()

so we need this as well:

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 565fec451d69..fab2235599a0 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -184,6 +184,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
                "do_group_exit",
                "stop_this_cpu",
                "__invalid_creds",
+               "cpu_startup_entry",
        };

        if (!func)