linux-kernel - Re: [PATCH v5 07/20] x86/kexec: Invoke copy of relocate

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Message-ID: <20241219222821.c6o3peznyzoxaslj@jpoimboe>
Date: Thu, 19 Dec 2024 14:28:21 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Nathan Chancellor <nathan@...nel.org>, kexec@...ts.infradead.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org, Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, bsz@...zon.de
Subject: Re: [PATCH v5 07/20] x86/kexec: Invoke copy of relocate_kernel()
 instead of the original

On Thu, Dec 19, 2024 at 11:02:55AM +0100, David Woodhouse wrote:
> On Wed, 2024-12-18 at 16:20 -0800, Josh Poimboeuf wrote:
> > Anyway, what I think you're looking for is UNWIND_HINT_UNDEFINED.  In
> > fact all the unwind annotations in that file should be UNDEFINED since
> > the hints are all referring to the wrong addresses (because copied code)
> > and the ORC unwinder isn't reachable for most of that code anyway.
> > 
> > Also, it's fine to make relocate_kernel() a proper function with
> > SYM_FUNC_END, you'd just need to add the following line afterwards:
> > 
> >   STACK_FRAME_NON_STANDARD relocate_kernel
> > 
> 
> Thanks, I'll take a look. The next thing objtool is actually
> complaining about is that relocate_kernel() itself is not reachable
> (since it's never invoked in its original location):
> 
> vmlinux.o: warning: objtool: relocate_kernel+0x0: unreachable instruction

Right, I think UNWIND_HINT_UNDEFINED should fix that.

-- 
Josh