linux-kernel - Re: [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET

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Date:   Tue, 31 Mar 2020 16:20:40 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org, x86@...nel.org,
        mhiramat@...nel.org, mbenes@...e.cz,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET

On Tue, Mar 31, 2020 at 04:17:58PM -0500, Josh Poimboeuf wrote:
> > I'm not against adding a second/separate hint for this. In fact, I
> > almost considered teaching objtool how to interpret the whole IRET frame
> > so that we can do it without hints. It's just that that's too much code
> > for this one case.
> > 
> > HINT_IRET_SELF ?
> 
> Despite my earlier complaint about stack size knowledge, we could just
> forget the hint and make "iretq in C code" equivalent to "reduce stack
> size by arch_exception_stack_size()" and keep going.  There's
> file->c_file which tells you it's a C file.

Or maybe "iretq in an STT_FUNC" is better since this pattern could
presumably happen in a callable asm function.

-- 
Josh