linux-kernel - Re: [PATCH v2] x86/ftrace: Remove OBJECT_FILES_NON

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Message-ID: <20220617185157.3c6f442a@gandalf.local.home>
Date:   Fri, 17 Jun 2022 18:51:57 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] x86/ftrace: Remove OBJECT_FILES_NON_STANDARD usage

On Fri,  3 Jun 2022 08:04:44 -0700
Josh Poimboeuf <jpoimboe@...nel.org> wrote:

> The file-wide OBJECT_FILES_NON_STANDARD annotation is used with
> CONFIG_FRAME_POINTER to tell objtool to skip the entire file when frame
> pointers are enabled.  However that annotation is now deprecated because
> it doesn't work with IBT, where objtool runs on vmlinux.o instead of
> individual translation units.
> 
> Instead, use more fine-grained function-specific annotations:
> 
> - The 'save_mcount_regs' macro does funny things with the frame pointer.
>   Use STACK_FRAME_NON_STANDARD_FP to tell objtool to ignore the
>   functions using it.
> 
> - The return_to_handler() "function" isn't actually a callable function.
>   Instead of being called, it's returned to.  The real return address
>   isn't on the stack, so unwinding is already doomed no matter which
>   unwinder is used.  So just remove the STT_FUNC annotation, telling
>   objtool to ignore it.  That also removes the implicit
>   ANNOTATE_NOENDBR, which now needs to be made explicit.
> 
> Fixes the following warning:
> 
>   vmlinux.o: warning: objtool: __fentry__+0x16: return with modified stack frame
> 
> Fixes: ed53a0d97192 ("x86/alternative: Use .ibt_endbr_seal to seal indirect calls")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
> v2:
> - fix return_to_handler()

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

-- Steve