On Thu, 17 Dec 2020 at 01:41, Nick Desaulniers ndesaulniers@google.com wrote:
With newer GNU binutils, linking with BFD produces warnings for vmlinux: aarch64-linux-gnu-ld: warning: -z norelro ignored
BFD can produce this warning when the target emulation mode does not support RELRO relocation types, and -z relro or -z norelro is passed.
RELRO is not a relocation type, it is a type of program header which we might simply ignore, if it weren't for the fact that it can only be emitted if the layout of the sections adheres to certain rules (and ours doesn't), and we get an error otherwise.
It amounts to implicit __ro_after_init annotations for statically initialized const pointers, but given that we don't compile with -fpie, those const pointers reside in .rodata already, so RELRO adds no value for us.
Alan Modra clarifies: The default linker emulation for an aarch64-linux ld.bfd is -maarch64linux, the default for an aarch64-elf linker is -maarch64elf. They are not equivalent. If you choose -maarch64elf you get an emulation that doesn't support -z relro.
The ARCH=arm64 kernel prefers -maarch64elf, but may fall back to -maarch64linux based on the toolchain configuration.
LLD will always create RELRO relocation types regardless of target emulation.
RELRO program header
To avoid the above warning when linking with BFD, pass -z norelro only when linking with LLD or with -maarch64linux.
Cc: Alan Modra amodra@gmail.com Cc: Ard Biesheuvel ardb@kernel.org Cc: Fāng-ruì Sòng maskray@google.com Fixes: 3b92fa7485eb ("arm64: link with -z norelro regardless of CONFIG_RELOCATABLE") Reported-by: kernelci.org bot bot@kernelci.org Reported-by: Quentin Perret qperret@google.com Signed-off-by: Nick Desaulniers ndesaulniers@google.com
With mentions of 'RELRO relocation types' fixed:
Acked-by: Ard Biesheuvel ardb@kernel.org
arch/arm64/Makefile | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 6be9b3750250..90309208bb28 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -10,7 +10,7 @@ # # Copyright (C) 1995-2001 by Russell King
-LDFLAGS_vmlinux :=--no-undefined -X -z norelro +LDFLAGS_vmlinux :=--no-undefined -X
ifeq ($(CONFIG_RELOCATABLE), y) # Pass --no-apply-dynamic-relocs to restore pre-binutils-2.27 behaviour @@ -115,16 +115,20 @@ KBUILD_CPPFLAGS += -mbig-endian CHECKFLAGS += -D__AARCH64EB__ # Prefer the baremetal ELF build target, but not all toolchains include # it so fall back to the standard linux version if needed. -KBUILD_LDFLAGS += -EB $(call ld-option, -maarch64elfb, -maarch64linuxb) +KBUILD_LDFLAGS += -EB $(call ld-option, -maarch64elfb, -maarch64linuxb -z norelro) UTS_MACHINE := aarch64_be else KBUILD_CPPFLAGS += -mlittle-endian CHECKFLAGS += -D__AARCH64EL__ # Same as above, prefer ELF but fall back to linux target if needed. -KBUILD_LDFLAGS += -EL $(call ld-option, -maarch64elf, -maarch64linux) +KBUILD_LDFLAGS += -EL $(call ld-option, -maarch64elf, -maarch64linux -z norelro) UTS_MACHINE := aarch64 endif
+ifeq ($(CONFIG_LD_IS_LLD), y) +KBUILD_LDFLAGS += -z norelro +endif
CHECKFLAGS += -D__aarch64__
ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS),y)
2.29.2.684.gfbc64c5ab5-goog