detectNativeCpuAndFeatures

pub fn detectNativeCpuAndFeatures(io: Io) ?Target.Cpu {
    var file = Io.Dir.openFileAbsolute(io, "/proc/cpuinfo", .{}) catch |err| switch (err) {
        else => return null,
    };
    defer file.close(io);

    var buffer: [4096]u8 = undefined; // "flags" lines can get pretty long.
    var file_reader = file.reader(io, &buffer);

    const current_arch = builtin.cpu.arch;
    return switch (current_arch) {
        .aarch64, .aarch64_be => b: {
            const registers = [12]u64{
                getAArch64CpuFeature("MIDR_EL1"),
                getAArch64CpuFeature("ID_AA64PFR0_EL1"),
                getAArch64CpuFeature("ID_AA64PFR1_EL1"),
                getAArch64CpuFeature("ID_AA64DFR0_EL1"),
                getAArch64CpuFeature("ID_AA64DFR1_EL1"),
                getAArch64CpuFeature("ID_AA64AFR0_EL1"),
                getAArch64CpuFeature("ID_AA64AFR1_EL1"),
                getAArch64CpuFeature("ID_AA64ISAR0_EL1"),
                getAArch64CpuFeature("ID_AA64ISAR1_EL1"),
                getAArch64CpuFeature("ID_AA64MMFR0_EL1"),
                getAArch64CpuFeature("ID_AA64MMFR1_EL1"),
                getAArch64CpuFeature("ID_AA64MMFR2_EL1"),
            };

            break :b @import("arm.zig").aarch64.detectNativeCpuAndFeatures(current_arch, registers);
        },
        .arm, .armeb, .thumb, .thumbeb => ArmCpuinfoParser.parse(current_arch, &file_reader.interface) catch null,
        .powerpc, .powerpcle, .powerpc64, .powerpc64le => PowerpcCpuinfoParser.parse(current_arch, &file_reader.interface) catch null,
        .riscv64, .riscv32 => b: {
            var cpu = (RiscvCpuinfoParser.parse(current_arch, &file_reader.interface) catch null) orelse cpu: {
                const model = Target.Cpu.Model.generic(current_arch);
                break :cpu Target.Cpu{
                    .arch = current_arch,
                    .model = model,
                    .features = model.features,
                };
            };

            riscv.detectCpuFeatures(&cpu);
            cpu.features.populateDependencies(cpu.arch.allFeaturesList());

            break :b cpu;
        },
        .s390x => S390xCpuinfoParser.parse(current_arch, &file_reader.interface) catch null,
        .sparc, .sparc64 => SparcCpuinfoParser.parse(current_arch, &file_reader.interface) catch null,
        else => null,
    };
}