linux-kernel - Re: [RFC/RFT PATCH 15/19] x64/acpi: Use PIC-compatible references in wakeup

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Message-ID: <CAMj1kXE59iJd-GGq4w0oZ99Lf7MswdOUSf11UASrqqWUUwW+zg@mail.gmail.com>
Date: Fri, 9 Jan 2026 13:10:22 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Kees Cook <kees@...nel.org>, 
	Uros Bizjak <ubizjak@...il.com>, linux-hardening@...r.kernel.org
Subject: Re: [RFC/RFT PATCH 15/19] x64/acpi: Use PIC-compatible references in wakeup_64.S

On Fri, 9 Jan 2026 at 13:09, Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Fri, 9 Jan 2026 at 12:46, Brian Gerst <brgerst@...il.com> wrote:
> >
> > On Fri, Jan 9, 2026 at 2:59 AM Ard Biesheuvel <ardb@...nel.org> wrote:
> > >
> > > On Fri, 9 Jan 2026 at 06:01, Brian Gerst <brgerst@...il.com> wrote:
> > > >
> > > > On Thu, Jan 8, 2026 at 4:28 AM Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > >
> > > > > Use ordinary RIP-relative references to make the code compatible with
> > > > > running the linker in PIE mode.
> > > > >
> > > > > Note that wakeup_long64() runs in the kernel's ordinary virtual mapping
> > > > > so there is no need to record the address of .Lresume_point in a global
> > > > > variable. And fix the comment while at it.
> > > > >
> > > > > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > > > > ---
> > > > >  arch/x86/kernel/acpi/wakeup_64.S | 11 ++++-------
> > > > >  1 file changed, 4 insertions(+), 7 deletions(-)
> > > > >
> > > > > diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
> > > > > index 04f561f75e99..15233a4e1c95 100644
> > > > > --- a/arch/x86/kernel/acpi/wakeup_64.S
> > > > > +++ b/arch/x86/kernel/acpi/wakeup_64.S
> > > > > @@ -14,7 +14,7 @@
> > > > >
> > > > >  .code64
> > > > >         /*
> > > > > -        * Hooray, we are in Long 64-bit mode (but still running in low memory)
> > > > > +        * Hooray, we are in Long 64-bit mode
> > > > >          */
> > > > >  SYM_FUNC_START(wakeup_long64)
> > > > >         ANNOTATE_NOENDBR
> > > > > @@ -41,7 +41,7 @@ SYM_FUNC_START(wakeup_long64)
> > > > >         movq    saved_rsi(%rip), %rsi
> > > > >         movq    saved_rbp(%rip), %rbp
> > > > >
> > > > > -       movq    saved_rip(%rip), %rax
> > > > > +       leaq    .Lresume_point(%rip), %rax
> > > > >         ANNOTATE_RETPOLINE_SAFE
> > > > >         jmp     *%rax
> > > >
> > > > If this is already running on the virtual mapping, this can simply be
> > > > changed to a direct jump.
> > > >
> > >
> > > Indeed, but I couldn't figure out how to do so without making objtool unhappy.
> >
> > I replaced it with a simple "jmp .Lresume_point" and objtool seemed
> > fine with it on a defconfig build.  What error did you see?
>
> arch/x86/kernel/acpi/wakeup_64.o: warning: objtool: wakeup_long64()
> falls through to next function do_suspend_lowlevel()

Note that this is x86_64_defconfig with CONFIG_X86_KERNEL_IBT disabled.