linux-kernel - Re: [PATCH v2] efistub: Only link libstub to final vmlinux

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Message-ID: <CAMj1kXEaxxcWTTANWeEMNjYDymdL5Fxy2B=XBF4RGtteEkfinw@mail.gmail.com>
Date: Tue, 28 Oct 2025 14:47:18 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	loongarch@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-efi@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] efistub: Only link libstub to final vmlinux

On Sun, 26 Oct 2025 at 12:20, Huacai Chen <chenhuacai@...nel.org> wrote:
>
> On Thu, Oct 23, 2025 at 4:07 PM Ard Biesheuvel <ardb@...nel.org> wrote:
> >
> > On Thu, 23 Oct 2025 at 10:01, Huacai Chen <chenhuacai@...nel.org> wrote:
> > >
> > > On Thu, Oct 23, 2025 at 2:55 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> > > >
> > > > Hi Josh and Ard,
> > > >
> > > > On 2025/10/20 下午2:55, Huacai Chen wrote:
> > > > > On Mon, Oct 20, 2025 at 9:24 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> > > > >>
> > > > >> Hi Josh, Ard and Huacai,
> > > > >>
> > > > >> On 2025/10/18 上午1:05, Josh Poimboeuf wrote:
> > > > >>
> > > > >> ...
> > > > >>
> > > > >>> But IIUC, the libstub code runs *very* early, and wouldn't show up in a
> > > > >>> stack trace anyway, because there are no traces of it on the stack once
> > > > >>> it branches to head.S code (which doesn't save the link register).
> > > > >>
> > > > >> Thanks for your discussions.
> > > > >>
> > > > >> Are you OK with this current patch?
> > > > > For me the current patch is just OK.
> > > >
> > > > We have discussed this a few times but there is almost no consensus
> > > > of what should happen next and nothing changes.
> > > >
> > > > Could you please give me a clear reply? Then I can make progress for
> > > > the following series:
> > > >
> > > > https://lore.kernel.org/loongarch/20250917112716.24415-1-yangtiezhu@loongson.cn/
> > > For me, this patch is OK, ignore __efistub_ prefix in objtool is also
> > > OK [1]. But I cannot accept the way that modifying the efistub part
> > > only for LoongArch.
> > >
> > > Clear enough?
> > >
> >
> > LoongArch is the only architecture which has the problem, so I don't
> > see a reason to modify other architectures.
> From your reply I think the efistub code is completely right, but
> objtool cannot handle the "noreturn" function pointer. And this patch
> is a workaround rather than a proper fix (so you don't want to touch
> other architectures), right?
>

That is my reasoning, yes. But Josh is right that it shouldn't make a
difference in practice, I am just reluctant to make changes to the
code running on the target to accommodate a flawed build time tool.