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

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Message-ID: <CAAhV-H5KsFShDJ_Cxu+1_ces8oojn8+S-7PLmE7aUj8gX5_GEw@mail.gmail.com>
Date: Mon, 10 Nov 2025 15:00:00 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Ard Biesheuvel <ardb@...nel.org>, 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 Mon, Nov 10, 2025 at 9:19 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
> On 2025/10/28 下午9:47, Ard Biesheuvel wrote:
> > 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.
>
> If I understand correctly, I should modify this patch to remove the
> changes of arm and riscv for now, do the changes only when there is
> a real problem or requirement some day, right? If no more comments,
> I will send v3 later.
Now everyone involved agrees that the efistub code is correct, so the
proper solution is to fix the compiler. Changing efistub code and
changing objtool (ignore __efistub prefix) are both workarounds, but I
think changing objtool is a little more reasonable. Maybe Josh has
different ideas?

Huacai

>
> Thanks,
> Tiezhu
>
>