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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the"License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an"AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// HERMETIC NOTE: The randen_hwaes target must not introduce duplicate
+// symbols from arbitrary system and other headers, since it may be built
+// with different flags from other targets, using different levels of
+// optimization, potentially introducing ODR violations.
+
+#include "absl/random/internal/randen_detect.h"
+
+#include <cstdint>
+#include <cstring>
+
+#include "absl/random/internal/platform.h"
+
+#if defined(ABSL_ARCH_X86_64)
+#define ABSL_INTERNAL_USE_X86_CPUID
+#elif defined(ABSL_ARCH_PPC) || defined(ABSL_ARCH_ARM) || \
+ defined(ABSL_ARCH_AARCH64)
+#if defined(__ANDROID__)
+#define ABSL_INTERNAL_USE_ANDROID_GETAUXVAL
+#define ABSL_INTERNAL_USE_GETAUXVAL
+#elif defined(__linux__)
+#define ABSL_INTERNAL_USE_LINUX_GETAUXVAL
+#define ABSL_INTERNAL_USE_GETAUXVAL
+#endif
+#endif
+
+#if defined(ABSL_INTERNAL_USE_X86_CPUID)
+#if defined(_WIN32) || defined(_WIN64)
+#include <intrin.h> // NOLINT(build/include_order)
+#pragma intrinsic(__cpuid)
+#else
+// MSVC-equivalent __cpuid intrinsic function.
+static void __cpuid(int cpu_info[4], int info_type) {
+ __asm__ volatile("cpuid \n\t"
+ : "=a"(cpu_info[0]), "=b"(cpu_info[1]), "=c"(cpu_info[2]),
+ "=d"(cpu_info[3])
+ : "a"(info_type), "c"(0));
+}
+#endif
+#endif // ABSL_INTERNAL_USE_X86_CPUID
+
+// On linux, just use the c-library getauxval call.
+#if defined(ABSL_INTERNAL_USE_LINUX_GETAUXVAL)
+
+extern "C" unsigned long getauxval(unsigned long type); // NOLINT(runtime/int)
+
+static uint32_t GetAuxval(uint32_t hwcap_type) {
+ return static_cast<uint32_t>(getauxval(hwcap_type));
+}
+
+#endif
+
+// On android, probe the system's C library for getauxval().
+// This is the same technique used by the android NDK cpu features library
+// as well as the google open-source cpu_features library.
+//
+// TODO(absl-team): Consider implementing a fallback of directly reading
+// /proc/self/auxval.
+#if defined(ABSL_INTERNAL_USE_ANDROID_GETAUXVAL)
+#include <dlfcn.h>
+
+static uint32_t GetAuxval(uint32_t hwcap_type) {
+ // NOLINTNEXTLINE(runtime/int)
+ typedef unsigned long (*getauxval_func_t)(unsigned long);
+
+ dlerror(); // Cleaning error state before calling dlopen.
+ void* libc_handle = dlopen("libc.so", RTLD_NOW);
+ if (!libc_handle) {
+ return 0;
+ }
+ uint32_t result = 0;
+ void* sym = dlsym(libc_handle, "getauxval");
+ if (sym) {
+ getauxval_func_t func;
+ memcpy(&func, &sym, sizeof(func));
+ result = static_cast<uint32_t>((*func)(hwcap_type));
+ }
+ dlclose(libc_handle);
+ return result;
+}
+
+#endif
+
+namespace absl {
+namespace random_internal {
+
+// The default return at the end of the function might be unreachable depending
+// on the configuration. Ignore that warning.
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunreachable-code-return"
+#endif
+
+// CPUSupportsRandenHwAes returns whether the CPU is a microarchitecture
+// which supports the crpyto/aes instructions or extensions necessary to use the
+// accelerated RandenHwAes implementation.
+//
+// 1. For x86 it is sufficient to use the CPUID instruction to detect whether
+// the cpu supports AES instructions. Done.
+//
+// Fon non-x86 it is much more complicated.
+//
+// 2. When ABSL_INTERNAL_USE_GETAUXVAL is defined, use getauxval() (either
+// the direct c-library version, or the android probing version which loads
+// libc), and read the hardware capability bits.
+// This is based on the technique used by boringssl uses to detect
+// cpu capabilities, and should allow us to enable crypto in the android
+// builds where it is supported.
+//
+// 3. Use the default for the compiler architecture.
+//
+
+bool CPUSupportsRandenHwAes() {
+#if defined(ABSL_INTERNAL_USE_X86_CPUID)
+ // 1. For x86: Use CPUID to detect the required AES instruction set.
+ int regs[4];
+ __cpuid(reinterpret_cast<int*>(regs), 1);
+ return regs[2] & (1 << 25); // AES
+
+#elif defined(ABSL_INTERNAL_USE_GETAUXVAL)
+ // 2. Use getauxval() to read the hardware bits and determine
+ // cpu capabilities.
+
+#define AT_HWCAP 16
+#define AT_HWCAP2 26
+#if defined(ABSL_ARCH_PPC)
+ // For Power / PPC: Expect that the cpu supports VCRYPTO
+ // See https://members.openpowerfoundation.org/document/dl/576
+ // VCRYPTO should be present in POWER8 >= 2.07.
+ // Uses Linux kernel constants from arch/powerpc/include/uapi/asm/cputable.h
+ static const uint32_t kVCRYPTO = 0x02000000;
+ const uint32_t hwcap = GetAuxval(AT_HWCAP2);
+ return (hwcap & kVCRYPTO) != 0;
+
+#elif defined(ABSL_ARCH_ARM)
+ // For ARM: Require crypto+neon
+ // http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0500f/CIHBIBBA.html
+ // Uses Linux kernel constants from arch/arm64/include/asm/hwcap.h
+ static const uint32_t kNEON = 1 << 12;
+ uint32_t hwcap = GetAuxval(AT_HWCAP);
+ if ((hwcap & kNEON) == 0) {
+ return false;
+ }
+
+ // And use it again to detect AES.
+ static const uint32_t kAES = 1 << 0;
+ const uint32_t hwcap2 = GetAuxval(AT_HWCAP2);
+ return (hwcap2 & kAES) != 0;
+
+#elif defined(ABSL_ARCH_AARCH64)
+ // For AARCH64: Require crypto+neon
+ // http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0500f/CIHBIBBA.html
+ static const uint32_t kNEON = 1 << 1;
+ static const uint32_t kAES = 1 << 3;
+ const uint32_t hwcap = GetAuxval(AT_HWCAP);
+ return ((hwcap & kNEON) != 0) && ((hwcap & kAES) != 0);
+#endif
+
+#else // ABSL_INTERNAL_USE_GETAUXVAL
+ // 3. By default, assume that the compiler default.
+ return ABSL_HAVE_ACCELERATED_AES ? true : false;
+
+#endif
+ // NOTE: There are some other techniques that may be worth trying:
+ //
+ // * Use an environment variable: ABSL_RANDOM_USE_HWAES
+ //
+ // * Rely on compiler-generated target-based dispatch.
+ // Using x86/gcc it might look something like this:
+ //
+ // int __attribute__((target("aes"))) HasAes() { return 1; }
+ // int __attribute__((target("default"))) HasAes() { return 0; }
+ //
+ // This does not work on all architecture/compiler combinations.
+ //
+ // * On Linux consider reading /proc/cpuinfo and/or /proc/self/auxv.
+ // These files have lines which are easy to parse; for ARM/AARCH64 it is quite
+ // easy to find the Features: line and extract aes / neon. Likewise for
+ // PPC.
+ //
+ // * Fork a process and test for SIGILL:
+ //
+ // * Many architectures have instructions to read the ISA. Unfortunately
+ // most of those require that the code is running in ring 0 /
+ // protected-mode.
+ //
+ // There are several examples. e.g. Valgrind detects PPC ISA 2.07:
+ // https://github.com/lu-zero/valgrind/blob/master/none/tests/ppc64/test_isa_2_07_part1.c
+ //
+ // MRS <Xt>, ID_AA64ISAR0_EL1 ; Read ID_AA64ISAR0_EL1 into Xt
+ //
+ // uint64_t val;
+ // __asm __volatile("mrs %0, id_aa64isar0_el1" :"=&r" (val));
+ //
+ // * Use a CPUID-style heuristic database.
+ //
+ // * On Apple (__APPLE__), AES is available on Arm v8.
+ // https://stackoverflow.com/questions/45637888/how-to-determine-armv8-features-at-runtime-on-ios
+}
+
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+
+} // namespace random_internal
+} // namespace absl