Messages in this thread | | | Date | Mon, 27 Feb 2023 14:27:11 +0100 | Subject | Re: [PATCH v7 1/1] riscv: Allow to downgrade paging mode from the command line | From | Alexandre Ghiti <> |
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On 2/27/23 13:56, Ard Biesheuvel wrote: > On Mon, 27 Feb 2023 at 13:32, Conor Dooley <conor.dooley@microchip.com> wrote: >> Hey Alex, clang/llvm folk, >> >> On Fri, Feb 24, 2023 at 11:02:18AM +0100, Alexandre Ghiti wrote: >>> Add 2 early command line parameters that allow to downgrade satp mode >>> (using the same naming as x86): >>> - "no5lvl": use a 4-level page table (down from sv57 to sv48) >>> - "no4lvl": use a 3-level page table (down from sv57/sv48 to sv39) >>> >>> Note that going through the device tree to get the kernel command line >>> works with ACPI too since the efi stub creates a device tree anyway with >>> the command line. >>> >>> In KASAN kernels, we can't use the libfdt that early in the boot process >>> since we are not ready to execute instrumented functions. So instead of >>> using the "generic" libfdt, we compile our own versions of those functions >>> that are not instrumented and that are prefixed so that they do not >>> conflict with the generic ones. We also need the non-instrumented versions >>> of the string functions and the prefixed versions of memcpy/memmove. >>> >>> This is largely inspired by commit aacd149b6238 ("arm64: head: avoid >>> relocating the kernel twice for KASLR") from which I removed compilation >>> flags that were not relevant to RISC-V at the moment (LTO, SCS, pie). >>> >>> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> >>> Tested-by: Björn Töpel <bjorn@rivosinc.com> >>> Reviewed-by: Björn Töpel <bjorn@rivosinc.com> >>> --- >>> .../admin-guide/kernel-parameters.txt | 5 +- >>> arch/riscv/kernel/Makefile | 2 + >>> arch/riscv/kernel/pi/Makefile | 37 +++++++++++ >>> arch/riscv/kernel/pi/cmdline_early.c | 62 +++++++++++++++++++ >> + 4 ld.lld: warning: vmlinux.a(arch/riscv/kernel/pi/string.pi.o):(.init.sdata) is being placed in '.init.sdata' >> >> I'm getting 4 new linker warnings with LLVM=1 clang-15 allmodconfig >> builds - but I don't really understand this issue. >> Is this spurious, and a just consequence of... >> >>> diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile >>> new file mode 100644 >>> index 000000000000..4002ed94b6d3 >>> --- /dev/null >>> +++ b/arch/riscv/kernel/pi/Makefile >>> @@ -0,0 +1,37 @@ >>> +# SPDX-License-Identifier: GPL-2.0 >>> +# This file was copied from arm64/kernel/pi/Makefile. >>> + >>> +KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \ >>> + -Os -DDISABLE_BRANCH_PROFILING $(DISABLE_STACKLEAK_PLUGIN) \ >>> + $(call cc-option,-mbranch-protection=none) \ >>> + -I$(srctree)/scripts/dtc/libfdt -fno-stack-protector \ >>> + -D__DISABLE_EXPORTS -ffreestanding \ >>> + -fno-asynchronous-unwind-tables -fno-unwind-tables \ >>> + $(call cc-option,-fno-addrsig) >>> + >>> +CFLAGS_cmdline_early.o += -D__NO_FORTIFY >>> +CFLAGS_lib-fdt_ro.o += -D__NO_FORTIFY >>> + >>> +GCOV_PROFILE := n >>> +KASAN_SANITIZE := n >>> +KCSAN_SANITIZE := n >>> +UBSAN_SANITIZE := n >>> +KCOV_INSTRUMENT := n >>> + >>> +$(obj)/%.pi.o: OBJCOPYFLAGS := --prefix-symbols=__pi_ \ >>> + --remove-section=.note.gnu.property \ >>> + --prefix-alloc-sections=.init >> ...this? >> > Yes. if the input object has a .sdata section, the output .pi.o object > will have a .init.sdata section, and if the common linker script does > not place it explicitly, you will get a warning. Note that we switched > to --orphan-handling=error on other arches, as the linker sometimes
It seems orphan-handling is set to "error" only when WERROR is set (see CONFIG_LD_ORPHAN_WARN_LEVEL).
> does unexpected things with sections it doesn't know about. > > I'd imagine this needs to be combined with .init.data
Yes, gcc does not produce this section but others that I placed in a new section called .init.pidata: I did not want to expand INIT_DATA_SECTION macro because we won't need that anymore when we implement all the string functions.
So I'll add this new .init.sdata section to .init.pidata in the v8!
Thanks,
> > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv
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