On Mon, Dec 14, 2020 at 3:18 PM Alan Modra amodra@gmail.com wrote:
On Mon, Dec 14, 2020 at 01:44:06PM -0800, Nick Desaulniers wrote:
aarch64-linux-gnu-ld: warning: -z norelro ignored
So we set the emulation mode via -maarch64elf, and our preprocessed
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.
Now I don't know why the kernel uses -maarch64elf so you shouldn't interpret my comment as a recommendation to use -maarch64linux instead. That may have other unwanted effects.
Cool, thanks for the context. The kernel currently has:
arch/arm64/Makefile: ... ifeq ($(CONFIG_CPU_BIG_ENDIAN), y) ... # Prefer the baremetal ELF build target, but not all toolchains include # it so fall back to the standard linux version if needed. LDFLAGS += -EB $(call ld-option, -maarch64elfb, -maarch64linuxb) ... else ... # Same as above, prefer ELF but fall back to linux target if needed. LDFLAGS += -EL $(call ld-option, -maarch64elf, -maarch64linux) ...
Then $ git log -S maarch64elf arch/arm64/Makefile provides more context: 1. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... 2. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... 3. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
So it seems more that the kernel is relying on whichever emulation targets are supported in local distros, not necessarily the semantic differences between the two. Since the kernel might be linked as either, I'll send the patch described in my last post to add `-z norelro` just when linking with LLD, since it sounds like it's only possible to specify when -maarch64linux/-maarch64linuxb is used, which is unlikely.