oaknut: feature_detect: Support OpenBSD

include/oaknut/feature_detection/feature_detection.hpp

@@ -15,6 +15,10 @@
 #    define OAKNUT_CPU_FEATURE_DETECTION 1
 #    define OAKNUT_SUPPORTS_READING_ID_REGISTERS 1
 #    include "oaknut/feature_detection/feature_detection_linux.hpp"
+#elif defined(__OpenBSD__)
+#    define OAKNUT_CPU_FEATURE_DETECTION 1
+#    define OAKNUT_SUPPORTS_READING_ID_REGISTERS 1
+#    include "oaknut/feature_detection/feature_detection_openbsd.hpp"
 #elif defined(_WIN32)
 #    define OAKNUT_CPU_FEATURE_DETECTION 1
 #    define OAKNUT_SUPPORTS_READING_ID_REGISTERS 2

include/oaknut/feature_detection/feature_detection_openbsd.hpp

@@ -0,0 +1,63 @@
+// SPDX-FileCopyrightText: Copyright (c) 2023 merryhime <https://mary.rs>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <optional>
+
+#include <sys/sysctl.h>
+#include <sys/types.h>
+
+#include "oaknut/feature_detection/cpu_feature.hpp"
+#include "oaknut/feature_detection/feature_detection_hwcaps.hpp"
+#include "oaknut/feature_detection/feature_detection_idregs.hpp"
+#include "oaknut/feature_detection/id_registers.hpp"
+
+namespace oaknut {
+
+namespace detail {
+
+inline std::uint64_t read_id_register(int index)
+{
+    uint64_t result = 0;
+    size_t result_size = sizeof(result);
+    std::array<int, 2> mib{CTL_MACHDEP, index};
+    if (sysctl(mib.data(), mib.size(), &result, &result_size, nullptr, 0) < 0)
+        return 0;
+    return result;
+}
+
+}  // namespace detail
+
+inline std::optional<id::IdRegisters> read_id_registers()
+{
+    // See OpenBSD source: sys/arch/arm64/include/cpu.h
+
+    return id::IdRegisters{
+        std::nullopt,                                   // No easy way of getting MIDR_EL1 other than reading /proc/cpu
+        id::Pfr0Register{detail::read_id_register(8)},  // CPU_ID_AA64PFR0
+        id::Pfr1Register{detail::read_id_register(9)},  // CPU_ID_AA64PFR1
+        id::Pfr2Register{0},
+        id::Zfr0Register{detail::read_id_register(11)},   // CPU_ID_AA64ZFR0
+        id::Smfr0Register{detail::read_id_register(10)},  // CPU_ID_AA64SMFR0
+        id::Isar0Register{detail::read_id_register(2)},   // CPU_ID_AA64ISAR0
+        id::Isar1Register{detail::read_id_register(3)},   // CPU_ID_AA64ISAR1
+        id::Isar2Register{detail::read_id_register(4)},   // CPU_ID_AA64ISAR2
+        id::Isar3Register{0},
+        id::Mmfr0Register{detail::read_id_register(5)},  // CPU_ID_AA64MMFR0
+        id::Mmfr1Register{detail::read_id_register(6)},  // CPU_ID_AA64MMFR1
+        id::Mmfr2Register{detail::read_id_register(7)},  // CPU_ID_AA64MMFR2
+        id::Mmfr3Register{0},
+        id::Mmfr4Register{0},
+    };
+}
+
+inline CpuFeatures detect_features()
+{
+    return detect_features_via_id_registers(*read_id_registers());
+}
+
+}  // namespace oaknut

include/oaknut/feature_detection/id_registers.hpp

@@ -5,6 +5,7 @@
 
 #include <cstddef>
 #include <cstdint>
+#include <optional>
 
 namespace oaknut::id {
 
@@ -297,7 +298,7 @@ struct Mmfr4Register {
 };
 
 struct IdRegisters {
-    std::uint64_t midr;
+    std::optional<std::uint64_t> midr;
     Pfr0Register pfr0;
     Pfr1Register pfr1;
     Pfr2Register pfr2;