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Subject[PATCH 1/5] arch: enable relative relocations for arm64, power, x86, s390 and x86
Date
Before updating certain subsystems to use place relative 32-bit
relocations in special sections, to save space and reduce the
number of absolute relocations that need to be processed at runtime
by relocatable kernels, introduce a new Kconfig symbol and define it
for some architectures that should be able to support and benefit
from it.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
arch/Kconfig | 10 ++++++++++
arch/arm64/Kconfig | 1 +
arch/arm64/kernel/vmlinux.lds.S | 2 +-
arch/powerpc/Kconfig | 1 +
arch/s390/Kconfig | 1 +
arch/x86/Kconfig | 1 +
6 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 21d0089117fe..4e77d8e8697e 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -940,4 +940,14 @@ config REFCOUNT_FULL
against various use-after-free conditions that can be used in
security flaw exploits.

+config HAVE_ARCH_PREL32_RELOCATIONS
+ bool
+ help
+ May be selected by an architecture if it supports place-relative
+ 32-bit relocations, both in the toolchain and in the module loader,
+ in which case relative references can be used in special sections
+ for PCI fixup, initcalls etc which are only half the size on 64 bit
+ architectures, and don't require runtime relocation on relocatable
+ kernels.
+
source "kernel/gcov/Kconfig"
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index dfd908630631..ce05d2d8143e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -72,6 +72,7 @@ config ARM64
select HAVE_ARCH_KGDB
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
+ select HAVE_ARCH_PREL32_RELOCATIONS
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
select HAVE_ARCH_TRANSPARENT_HUGEPAGE
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 987a00ee446c..5849bd4e2b06 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -171,7 +171,7 @@ SECTIONS
CON_INITCALL
SECURITY_INITCALL
INIT_RAM_FS
- *(.init.rodata.* .init.bss) /* from the EFI stub */
+ *(.init.rodata.* .init.bss .init.discard.*) /* from the EFI stub */
}
.exit.data : {
ARM_EXIT_KEEP(EXIT_DATA)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 36f858c37ca7..f7e60ed5bdd0 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -163,6 +163,7 @@ config PPC
select HAVE_ARCH_KGDB
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
+ select HAVE_ARCH_PREL32_RELOCATIONS
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
select ARCH_HAS_STRICT_KERNEL_RWX if (PPC_BOOK3S_64 && !RELOCATABLE && !HIBERNATION)
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 7eeb75d758c1..1206cc7daa0d 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -127,6 +127,7 @@ config S390
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_JUMP_LABEL
select CPU_NO_EFFICIENT_FFS if !HAVE_MARCH_Z9_109_FEATURES
+ select HAVE_ARCH_PREL32_RELOCATIONS
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_SOFT_DIRTY
select HAVE_ARCH_TRACEHOOK
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 781521b7cf9e..77246125883e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -112,6 +112,7 @@ config X86
select HAVE_ARCH_MMAP_RND_BITS if MMU
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT
select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT
+ select HAVE_ARCH_PREL32_RELOCATIONS
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
select HAVE_ARCH_TRANSPARENT_HUGEPAGE
--
2.11.0
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