From 5cf896fb6be3effd9aea455b22213e27be8bdb1d Mon Sep 17 00:00:00 2001 From: Peter Collingbourne Date: Wed, 31 Jul 2019 18:18:42 -0700 Subject: arm64: Add support for relocating the kernel with RELR relocations RELR is a relocation packing format for relative relocations. The format is described in a generic-abi proposal: https://groups.google.com/d/topic/generic-abi/bX460iggiKg/discussion The LLD linker can be instructed to pack relocations in the RELR format by passing the flag --pack-dyn-relocs=relr. This patch adds a new config option, CONFIG_RELR. Enabling this option instructs the linker to pack vmlinux's relative relocations in the RELR format, and causes the kernel to apply the relocations at startup along with the RELA relocations. RELA relocations still need to be applied because the linker will emit RELA relative relocations if they are unrepresentable in the RELR format (i.e. address not a multiple of 2). Enabling CONFIG_RELR reduces the size of a defconfig kernel image with CONFIG_RANDOMIZE_BASE by 3.5MB/16% uncompressed, or 550KB/5% compressed (lz4). Signed-off-by: Peter Collingbourne Tested-by: Nick Desaulniers Reviewed-by: Nick Desaulniers Signed-off-by: Will Deacon --- arch/Kconfig | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'arch/Kconfig') diff --git a/arch/Kconfig b/arch/Kconfig index a7b57dd42c26..aa6bdb3df5c1 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -925,6 +925,20 @@ config LOCK_EVENT_COUNTS the chance of application behavior change because of timing differences. The counts are reported via debugfs. +# Select if the architecture has support for applying RELR relocations. +config ARCH_HAS_RELR + bool + +config RELR + bool "Use RELR relocation packing" + depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR + default y + help + Store the kernel's dynamic relocations in the RELR relocation packing + format. Requires a compatible linker (LLD supports this feature), as + well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy + are compatible). + source "kernel/gcov/Kconfig" source "scripts/gcc-plugins/Kconfig" -- cgit v1.2.3