ld.lld does not support the NOCROSSREFS directive at the moment, which
breaks the build after commit b9baf5c8c5c3 ("ARM: Spectre-BHB
workaround"):
ld.lld: error: ./arch/arm/kernel/vmlinux.lds:34: AT expected, but got NOCROSSREFS
Support for this directive will eventually be implemented, at which
point a version check can be added. To avoid breaking the build in the
meantime, just define NOCROSSREFS to nothing when using ld.lld, with a
link to the issue for tracking.
Cc: stable(a)vger.kernel.org
Fixes: b9baf5c8c5c3 ("ARM: Spectre-BHB workaround")
Link: https://github.com/ClangBuiltLinux/linux/issues/1609
Signed-off-by: Nathan Chancellor <nathan(a)kernel.org>
---
Since b9baf5c8c5c3 has been backported to stable, I have marked this for
stable as well, using a Fixes tag to notate that this should go back to
all releases that have b9baf5c8c5c3, not to indicate any blame of
b9baf5c8c5c3, as this is clearly an ld.lld deficiency.
It would be nice if this could be applied directly to unblock our CI if
there are no objections.
arch/arm/include/asm/vmlinux.lds.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/arm/include/asm/vmlinux.lds.h b/arch/arm/include/asm/vmlinux.lds.h
index 0ef21bfae9f6..fad45c884e98 100644
--- a/arch/arm/include/asm/vmlinux.lds.h
+++ b/arch/arm/include/asm/vmlinux.lds.h
@@ -26,6 +26,14 @@
#define ARM_MMU_DISCARD(x) x
#endif
+/*
+ * ld.lld does not support NOCROSSREFS:
+ * https://github.com/ClangBuiltLinux/linux/issues/1609
+ */
+#ifdef CONFIG_LD_IS_LLD
+#define NOCROSSREFS
+#endif
+
/* Set start/end symbol names to the LMA for the section */
#define ARM_LMA(sym, section) \
sym##_start = LOADADDR(section); \
base-commit: e7e19defa57580d679bf0d03f8a34933008a7930
--
2.35.1
When building arm64 defconfig + CONFIG_LTO_CLANG_{FULL,THIN}=y after
commit 558c303c9734 ("arm64: Mitigate spectre style branch history side
channels"), the following error occurs:
<instantiation>:4:2: error: invalid fixup for movz/movk instruction
mov w0, #ARM_SMCCC_ARCH_WORKAROUND_3
^
Marc figured out that moving "#include <linux/init.h>" in
include/linux/arm-smccc.h into a !__ASSEMBLY__ block resolves it. The
full include chain with CONFIG_LTO=y from include/linux/arm-smccc.h:
include/linux/init.h
include/linux/compiler.h
arch/arm64/include/asm/rwonce.h
arch/arm64/include/asm/alternative-macros.h
arch/arm64/include/asm/assembler.h
The asm/alternative-macros.h include in asm/rwonce.h only happens when
CONFIG_LTO is set, which ultimately casues asm/assembler.h to be
included before the definition of ARM_SMCCC_ARCH_WORKAROUND_3. As a
result, the preprocessor does not expand ARM_SMCCC_ARCH_WORKAROUND_3 in
__mitigate_spectre_bhb_fw, which results in the error above.
Avoid this problem by just avoiding the CONFIG_LTO=y __READ_ONCE() block
in asm/rwonce.h with assembly files, as nothing in that block is useful
to assembly files, which allows ARM_SMCCC_ARCH_WORKAROUND_3 to be
properly expanded with CONFIG_LTO=y builds.
Cc: stable(a)vger.kernel.org
Fixes: e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y")
Link: https://lore.kernel.org/r/20220309155716.3988480-1-maz@kernel.org/
Reported-by: Marc Zyngier <maz(a)kernel.org>
Acked-by: James Morse <james.morse(a)arm.com>
Signed-off-by: Nathan Chancellor <nathan(a)kernel.org>
---
This is based on current mainline; if it should be based on a specific
arm64 branch, please let me know.
As 558c303c9734 is going to stable, I marked this for stable as well to
avoid breaking Android. I used e35123d83ee3 for the fixes tag to make it
clear to the stable team this should only go where that commit is
present. If a different fixes tag should be used, please feel free to
substitute.
arch/arm64/include/asm/rwonce.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h
index 1bce62fa908a..56f7b1d4d54b 100644
--- a/arch/arm64/include/asm/rwonce.h
+++ b/arch/arm64/include/asm/rwonce.h
@@ -5,7 +5,7 @@
#ifndef __ASM_RWONCE_H
#define __ASM_RWONCE_H
-#ifdef CONFIG_LTO
+#if defined(CONFIG_LTO) && !defined(__ASSEMBLY__)
#include <linux/compiler_types.h>
#include <asm/alternative-macros.h>
@@ -66,7 +66,7 @@
})
#endif /* !BUILD_VDSO */
-#endif /* CONFIG_LTO */
+#endif /* CONFIG_LTO && !__ASSEMBLY__ */
#include <asm-generic/rwonce.h>
base-commit: 330f4c53d3c2d8b11d86ec03a964b86dc81452f5
--
2.35.1