ld.lld prior to 21.0.0 does not support using the KEEP keyword within an overlay description, which may be needed to avoid discarding necessary sections within an overlay with '--gc-sections', which can be enabled for the kernel via CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.

Disallow CONFIG_LD_DEAD_CODE_DATA_ELIMINATION without support for KEEP within OVERLAY and introduce a macro, OVERLAY_KEEP, that can be used to conditionally add KEEP when it is properly supported to avoid breaking old versions of ld.lld.

Cc: stable@vger.kernel.org Link: https://github.com/llvm/llvm-project/commit/381599f1fe973afad3094e55ec99b162... Signed-off-by: Nathan Chancellor nathan@kernel.org --- arch/arm/Kconfig | 2 +- arch/arm/include/asm/vmlinux.lds.h | 6 ++++++ init/Kconfig | 5 +++++ 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 835b5f100e92..f3f6b7a33b79 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -121,7 +121,7 @@ config ARM select HAVE_KERNEL_XZ select HAVE_KPROBES if !XIP_KERNEL && !CPU_ENDIAN_BE32 && !CPU_V7M select HAVE_KRETPROBES if HAVE_KPROBES - select HAVE_LD_DEAD_CODE_DATA_ELIMINATION if (LD_VERSION >= 23600 || LD_IS_LLD) + select HAVE_LD_DEAD_CODE_DATA_ELIMINATION if (LD_VERSION >= 23600 || LD_CAN_USE_KEEP_IN_OVERLAY) select HAVE_MOD_ARCH_SPECIFIC select HAVE_NMI select HAVE_OPTPROBES if !THUMB2_KERNEL diff --git a/arch/arm/include/asm/vmlinux.lds.h b/arch/arm/include/asm/vmlinux.lds.h index d60f6e83a9f7..0f8ef1ed725e 100644 --- a/arch/arm/include/asm/vmlinux.lds.h +++ b/arch/arm/include/asm/vmlinux.lds.h @@ -34,6 +34,12 @@ #define NOCROSSREFS #endif

+#ifdef CONFIG_LD_CAN_USE_KEEP_IN_OVERLAY +#define OVERLAY_KEEP(x) KEEP(x) +#else +#define OVERLAY_KEEP(x) x +#endif + /* Set start/end symbol names to the LMA for the section */ #define ARM_LMA(sym, section) \ sym##_start = LOADADDR(section); \ diff --git a/init/Kconfig b/init/Kconfig index d0d021b3fa3b..fc994f5cd5db 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -129,6 +129,11 @@ config CC_HAS_COUNTED_BY # https://github.com/llvm/llvm-project/pull/112636 depends on !(CC_IS_CLANG && CLANG_VERSION < 190103)

+config LD_CAN_USE_KEEP_IN_OVERLAY + # ld.lld prior to 21.0.0 did not support KEEP within an overlay description + # https://github.com/llvm/llvm-project/pull/130661 + def_bool LD_IS_BFD || LLD_VERSION >= 210000 + config RUSTC_HAS_COERCE_POINTEE def_bool RUSTC_VERSION >= 108400

From: Christian Eggers ceggers@arri.de

Without this, the vectors are removed if LD_DEAD_CODE_DATA_ELIMINATION is enabled. At startup, the CPU (silently) hangs in the undefined instruction exception as soon as the first timer interrupt arrives.

On my setup, the system also boots fine without the 2nd and 3rd KEEP() statements, so I cannot tell whether these are actually required.

Cc: stable@vger.kernel.org Fixes: ed0f94102251 ("ARM: 9404/1: arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION") Signed-off-by: Christian Eggers ceggers@arri.de [nathan: Use OVERLAY_KEEP() to avoid breaking old ld.lld versions] Signed-off-by: Nathan Chancellor nathan@kernel.org --- arch/arm/include/asm/vmlinux.lds.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/vmlinux.lds.h b/arch/arm/include/asm/vmlinux.lds.h index 0f8ef1ed725e..14811b4f48ec 100644 --- a/arch/arm/include/asm/vmlinux.lds.h +++ b/arch/arm/include/asm/vmlinux.lds.h @@ -131,13 +131,13 @@ __vectors_lma = .; \ OVERLAY 0xffff0000 : NOCROSSREFS AT(__vectors_lma) { \ .vectors { \ - *(.vectors) \ + OVERLAY_KEEP(*(.vectors)) \ } \ .vectors.bhb.loop8 { \ - *(.vectors.bhb.loop8) \ + OVERLAY_KEEP(*(.vectors.bhb.loop8)) \ } \ .vectors.bhb.bpiall { \ - *(.vectors.bhb.bpiall) \ + OVERLAY_KEEP(*(.vectors.bhb.bpiall)) \ } \ } \ ARM_LMA(__vectors, .vectors); \