Commit b9495de1 authored by Nicholas Sielicki's avatar Nicholas Sielicki
Browse files

kernel/common-config: arm: configure alignment traps 

under armv7l, config.gz already had CONFIG_ALIGNMENT_TRAP=y, but
explicitly enable it and provide some context for the option.

under aarch64, on kernels that are new enough to support it, specify
CONFIG_COMPAT_ALIGNMENT_FIXUPS=y to attempt to resolve alignment
faults identically to how they are handled under 32-bit kernels. This
minimizes the potential for aarch32 userspace to behave differently
under an aarch64 kernel.
parent e3f328b0

pkgs/os-specific/linux/kernel/common-config.nix

+22 −0
Original line number Diff line number Diff line
@@ -1071,6 +1071,28 @@ let 
      # Keeping it a built-in ensures it will be used if possible.

      FB_SIMPLE = yes;



      # https://docs.kernel.org/arch/arm/mem_alignment.html

      # tldr:

      #  when buggy userspace code emits illegal misaligned LDM, STM,

      #  LDRD and STRDs, the instructions trap, are caught, and then

      #  are emulated by the kernel.

      #

      #  This is the default on armv7l, anyway, but it is explicitly

      #  enabled here for the sake of providing context for the

      #  aarch64 compat option which follows.

      ALIGNMENT_TRAP = mkIf (stdenv.hostPlatform.system == "armv7l-linux") yes;



      # https://patchwork.kernel.org/project/linux-arm-kernel/patch/20220701135322.3025321-1-ardb@kernel.org/

      # tldr:

      #  when encountering alignment faults under aarch64, this option

      #  makes the kernel attempt to handle the fault by doing the

      #  same style of misaligned emulation that is performed under

      #  armv7l (see above option).

      #

      #  This minimizes the potential for aarch32 userspace to behave

      #  differently when run under aarch64 kernels compared to when

      #  it is run under an aarch32 kernel.

      COMPAT_ALIGNMENT_FIXUPS = mkIf (stdenv.hostPlatform.system == "aarch64-linux") (whenAtLeast "6.1" yes);

    } // optionalAttrs (versionAtLeast version "5.4" && (stdenv.hostPlatform.system == "x86_64-linux" || stdenv.hostPlatform.system == "aarch64-linux")) {

      # Required for various hardware features on Chrome OS devices

      CHROME_PLATFORMS = yes;