Crc: Detect support for pmull and crc instructions on Apple AArch64

With a newer clang, we can use __builtin_cpu_supports which caches all
the feature bits.

If we are using an older clang, we fall back to querying sysctlbyname
for the relevant processor features.

PiperOrigin-RevId: 715153229
Change-Id: I570fa349f96829d5da3b32c928480ddf67176cad

absl/crc/BUILD.bazel

@@ -42,6 +42,7 @@ cc_library(
     deps = [
         "//absl/base",
         "//absl/base:config",
+        "//absl/types:optional",
     ],
 )
 

absl/crc/CMakeLists.txt

@@ -25,6 +25,7 @@ absl_cc_library(
   DEPS
     absl::base
     absl::config
+    absl::optional
 )
 
 # Internal-only target, do not depend on directly.

absl/crc/internal/cpu_detect.cc

@@ -18,12 +18,21 @@
 #include <string>
 
 #include "absl/base/config.h"
+#include "absl/types/optional.h"  // IWYU pragma: keep
 
 #if defined(__aarch64__) && defined(__linux__)
 #include <asm/hwcap.h>
 #include <sys/auxv.h>
 #endif
 
+#if defined(__aarch64__) && defined(__APPLE__)
+#if defined(__has_include) && __has_include(<arm/cpu_capabilities_public.h>)
+#include <arm/cpu_capabilities_public.h>
+#endif
+#include <sys/sysctl.h>
+#include <sys/types.h>
+#endif
+
 #if defined(_WIN32) || defined(_WIN64)
 #include <intrin.h>
 #endif
@@ -277,6 +286,61 @@ bool SupportsArmCRC32PMULL() {
 #endif
 }
 
+#elif defined(__aarch64__) && defined(__APPLE__)
+
+CpuType GetCpuType() { return CpuType::kUnknown; }
+
+template <typename T>
+static absl::optional<T> ReadSysctlByName(const char* name) {
+  T val;
+  size_t val_size = sizeof(T);
+  int ret = sysctlbyname(name, &val, &val_size, nullptr, 0);
+  if (ret == -1) {
+    return std::nullopt;
+  }
+  return val;
+}
+
+bool SupportsArmCRC32PMULL() {
+#if ABSL_HAVE_BUILTIN(__builtin_cpu_supports)
+  // Support for the AES and PMULL instructions are tied together:
+  // "When Cryptographic extensions are implemented and enabled then AESE, AESD,
+  // AESMC, and AESIMC instructions are implemented and also PMULL/PMULL2
+  // instructions operating on 64-bit data quantities."
+  //
+  // __builtin_cpu_supports expects users of PMULL to check for AES.
+  //
+  // https://developer.arm.com/documentation/101800/0201/AArch64-registers/AArch64-Identification-register-summary/ID-AA64ISAR0-EL1--AArch64-Instruction-Set-Attribute-Register-0
+  return __builtin_cpu_supports("crc+aes");
+#endif
+
+  // Newer XNU kernels support querying all capabilities in a single
+  // sysctlbyname.
+#if defined(CAP_BIT_CRC32) && defined(CAP_BIT_FEAT_PMULL)
+  static const absl::optional<uint64_t> caps =
+      ReadSysctlByName<uint64_t>("hw.optional.arm.caps");
+  if (caps.has_value()) {
+    constexpr uint64_t kCrc32AndPmullCaps =
+        (uint64_t{1} << CAP_BIT_CRC32) | (uint64_t{1} << CAP_BIT_FEAT_PMULL);
+    return (*caps & kCrc32AndPmullCaps) == kCrc32AndPmullCaps;
+  }
+#endif
+
+  // https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics#3915619
+  static const absl::optional<int> armv8_crc32 =
+      ReadSysctlByName<int>("hw.optional.armv8_crc32");
+  if (armv8_crc32.value_or(0) == 0) {
+    return false;
+  }
+  // https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics#3918855
+  static const absl::optional<int> feat_pmull =
+      ReadSysctlByName<int>("hw.optional.arm.FEAT_PMULL");
+  if (feat_pmull.value_or(0) == 0) {
+    return false;
+  }
+  return true;
+}
+
 #else
 
 CpuType GetCpuType() { return CpuType::kUnknown; }