linux-kernel - Re: [PATCH] arm64: Disable LLD linker ASSERT()s for the time being

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Message-ID: <20250602100932.GA919@willie-the-truck>
Date: Mon, 2 Jun 2025 11:09:32 +0100
From: Will Deacon <will@...nel.org>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>, Ard Biesheuvel <ardb+git@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, catalin.marinas@....com,
	nathan@...nel.org
Subject: Re: [PATCH] arm64: Disable LLD linker ASSERT()s for the time being

On Fri, May 30, 2025 at 04:23:16PM +0200, Ard Biesheuvel wrote:
> On Fri, 30 May 2025 at 15:38, Will Deacon <will@...nel.org> wrote:
> >
> > On Thu, May 29, 2025 at 09:35:08AM +0200, Ard Biesheuvel wrote:
> > > From: Ard Biesheuvel <ardb@...nel.org>
> > >
> > > It turns out that the way LLD handles ASSERT()s in the linker script can
> > > result in spurious failures, so disable them for the newly introduced
> > > BSS symbol export checks.
> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/2094
> > > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > > ---
> > >  arch/arm64/kernel/image-vars.h | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> > > index c5266430284b..86f088a16147 100644
> > > --- a/arch/arm64/kernel/image-vars.h
> > > +++ b/arch/arm64/kernel/image-vars.h
> > > @@ -10,6 +10,10 @@
> > >  #error This file should only be included in vmlinux.lds.S
> > >  #endif
> > >
> > > +#if defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 210000
> > > +#define ASSERT(...)
> > > +#endif
> > > +
> > >  #define PI_EXPORT_SYM(sym)           \
> > >       __PI_EXPORT_SYM(sym, __pi_ ## sym, Cannot export BSS symbol sym to startup code)
> > >  #define __PI_EXPORT_SYM(sym, pisym, msg)\
> > > @@ -142,4 +146,6 @@ KVM_NVHE_ALIAS(kvm_protected_mode_initialized);
> > >  _kernel_codesize = ABSOLUTE(__inittext_end - _text);
> > >  #endif
> > >
> > > +#undef ASSERT
> >
> > What about the ASSERT()s at the end of vmlinux.lds.S? Are they not
> > affected by the bug, for some reason?
> >
> > Also, even with this patch applied, I still see a link failure:
> >
> >   | ld.lld: error: assignment to symbol __init_end does not converge
> >
> > with the .config you sent me off-list.
> >
> 
> That is a different error that has been lurking for a while now; Arnd
> occasionally hits it but I haven't seen any other reports of it. AIUI,
> the issue is that INIT_IDMAP_DIR_PAGES and INIT_DIR_SIZE are defined
> in terms of (_end - KIMAGE_VADDR), resulting in a circular dependency.

Ok, I'll ignore that one for the moment, then...

> The config in the kernel test robot's report [0] appears to build fine
> with this patch applied.
> 
> 
> [0] https://lore.kernel.org/all/202505261019.OUlitN6m-lkp@intel.com/T/#u

... but I'm still not sure why the ASSERT()s in vmlinux.lds.S are not
affected. Is it just that we've not hit a .config which breaks with
those yet, or is it something more fundamental than that? I'd have
thought we'd need to so something like below (on top of your patch) to
fix this issue properly.

Will

--->8

diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index 86f088a16147..c5266430284b 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -10,10 +10,6 @@
 #error This file should only be included in vmlinux.lds.S
 #endif
 
-#if defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 210000
-#define ASSERT(...)
-#endif
-
 #define PI_EXPORT_SYM(sym)		\
 	__PI_EXPORT_SYM(sym, __pi_ ## sym, Cannot export BSS symbol sym to startup code)
 #define __PI_EXPORT_SYM(sym, pisym, msg)\
@@ -146,6 +142,4 @@ KVM_NVHE_ALIAS(kvm_protected_mode_initialized);
 _kernel_codesize = ABSOLUTE(__inittext_end - _text);
 #endif
 
-#undef ASSERT
-
 #endif /* __ARM64_KERNEL_IMAGE_VARS_H */
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index e4a525a865c1..3f7a365f7113 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -150,6 +150,10 @@ PECOFF_FILE_ALIGNMENT = 0x200;
 #define PECOFF_EDATA_PADDING
 #endif
 
+#if defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 210000
+#define ASSERT(...)
+#endif
+
 SECTIONS
 {
 	/*