linux-kernel - Re: [PATCH 16/21] x86/ftrace: Support objtool vmlinux.o validation in ftrace

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Date:   Thu, 14 Jan 2021 15:42:49 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 16/21] x86/ftrace: Support objtool vmlinux.o validation
 in ftrace_64.S

On Thu, 14 Jan 2021 13:40:12 -0600
Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> With objtool vmlinux.o validation of return_to_handler(), now that
> objtool has visibility inside the retpoline, jumping from EMPTY state to
> a proper function state results in a stack state mismatch.
> 
> return_to_handler() is actually quite normal despite the underlying
> magic.  Just annotate it as a normal function.

If you say so ;-)

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> 
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  arch/x86/kernel/ftrace_64.S | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
> index 1bf568d901b1..7c273846c687 100644
> --- a/arch/x86/kernel/ftrace_64.S
> +++ b/arch/x86/kernel/ftrace_64.S
> @@ -334,8 +334,7 @@ SYM_FUNC_START(ftrace_graph_caller)
>  	retq
>  SYM_FUNC_END(ftrace_graph_caller)
>  
> -SYM_CODE_START(return_to_handler)
> -	UNWIND_HINT_EMPTY
> +SYM_FUNC_START(return_to_handler)
>  	subq  $24, %rsp
>  
>  	/* Save the return values */
> @@ -350,5 +349,5 @@ SYM_CODE_START(return_to_handler)
>  	movq (%rsp), %rax
>  	addq $24, %rsp
>  	JMP_NOSPEC rdi
> -SYM_CODE_END(return_to_handler)
> +SYM_FUNC_END(return_to_handler)
>  #endif