linux-kernel - Re: [PATCH 00/10] ftrace: Add register_ftrace

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Date:   Mon, 11 Nov 2019 09:47:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        X86 ML <x86@...nel.org>, Nadav Amit <nadav.amit@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH 00/10] ftrace: Add register_ftrace_direct()

On Fri, Nov 08, 2019 at 04:51:00PM -0600, Josh Poimboeuf wrote:

> From: Josh Poimboeuf <jpoimboe@...hat.com>
> Subject: [PATCH] ftrace/x86: Tell objtool to ignore nondeterministic ftrace stack layout
> 
> Objtool complains about the new ftrace direct trampoline code:
> 
>   arch/x86/kernel/ftrace_64.o: warning: objtool: ftrace_regs_caller()+0x190: stack state mismatch: cfa1=7+16 cfa2=7+24
> 
> Typically, code has a deterministic stack layout, such that at a given
> instruction address, the stack frame size is always the same.
> 
> That's not the case for the new ftrace_regs_caller() code after it
> adjusts the stack for the direct case.  Just plead ignorance and assume
> it's always the non-direct path.  Note this creates a tiny window for
> ORC to get confused.

How is that not a problem for livepatch?