chromium/third_party/abseil-cpp/absl/random/internal/randen_detect.cc

// 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(__UCLIBC__) && defined(__GLIBC__) && \
    (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 16))
#define ABSL_HAVE_GETAUXVAL
#endif

#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__) && defined(ABSL_HAVE_GETAUXVAL)
#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)
#elif ABSL_HAVE_BUILTIN(__cpuid)
// MSVC-equivalent __cpuid intrinsic declaration for clang-like compilers
// for non-Windows build environments.
extern void __cpuid(int[4], int);
#else
// MSVC-equivalent __cpuid intrinsic function.
static void __cpuid(int cpu_info[4], int info_type) { … }
#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 {
ABSL_NAMESPACE_BEGIN
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(__clang__)
#pragma clang diagnostic pop
#endif

}  // namespace random_internal
ABSL_NAMESPACE_END
}  // namespace absl