libartbase/base/file_utils.cc - SHIFTPHONES/android_art - Gitiles

 /*
  * Copyright (C) 2011 The Android Open Source Project
  *
  * 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
  *
  *      http://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.
  */

 #include "file_utils.h"

 #include <inttypes.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #ifndef _WIN32
 #include <sys/wait.h>
 #endif
 #include <unistd.h>

 // We need dladdr.
 #if !defined(__APPLE__) && !defined(_WIN32)
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE
 #define DEFINED_GNU_SOURCE
 #endif
 #include <dlfcn.h>
 #include <libgen.h>
 #ifdef DEFINED_GNU_SOURCE
 #undef _GNU_SOURCE
 #undef DEFINED_GNU_SOURCE
 #endif
 #endif


 #include <memory>

 #include "android-base/stringprintf.h"
 #include "android-base/strings.h"

 #include "base/bit_utils.h"
 #include "base/globals.h"
 #include "base/os.h"
 #include "base/stl_util.h"
 #include "base/unix_file/fd_file.h"

 #if defined(__APPLE__)
 #include <crt_externs.h>
 #include <sys/syscall.h>
 #include "AvailabilityMacros.h"  // For MAC_OS_X_VERSION_MAX_ALLOWED
 #endif

 #if defined(__linux__)
 #include <linux/unistd.h>
 #endif

 namespace art {

 using android::base::StringPrintf;

 static constexpr const char* kClassesDex = "classes.dex";
 static constexpr const char* kApexDefaultPath = "/apex/";
 static constexpr const char* kAndroidRootEnvVar = "ANDROID_ROOT";
 static constexpr const char* kAndroidRootDefaultPath = "/system";
 static constexpr const char* kAndroidDataEnvVar = "ANDROID_DATA";
 static constexpr const char* kAndroidDataDefaultPath = "/data";
 static constexpr const char* kAndroidArtRootEnvVar = "ANDROID_ART_ROOT";
 static constexpr const char* kAndroidArtApexDefaultPath = "/apex/com.android.art";
 static constexpr const char* kAndroidConscryptRootEnvVar = "ANDROID_CONSCRYPT_ROOT";
 static constexpr const char* kAndroidConscryptApexDefaultPath = "/apex/com.android.conscrypt";

 // Get the "root" directory containing the "lib" directory where this instance
 // of the libartbase library (which contains `GetRootContainingLibartbase`) is
 // located:
 // - on host this "root" is normally the Android Root (e.g. something like
 //   "$ANDROID_BUILD_TOP/out/host/linux-x86/");
 // - on target this "root" is normally the ART Root ("/apex/com.android.art").
 // Return the empty string if that directory cannot be found or if this code is
 // run on Windows or macOS.
 static std::string GetRootContainingLibartbase() {
 #if !defined( _WIN32) && !defined(__APPLE__)
   // Check where libartbase is from, and derive from there.
   Dl_info info;
   if (dladdr(reinterpret_cast<const void*>(&GetRootContainingLibartbase), /* out */ &info) != 0) {
     // Make a duplicate of the fname so dirname can modify it.
     UniqueCPtr<char> fname(strdup(info.dli_fname));

     char* dir1 = dirname(fname.get());  // This is the lib directory.
     char* dir2 = dirname(dir1);         // This is the "root" directory.
     if (OS::DirectoryExists(dir2)) {
       std::string tmp = dir2;  // Make a copy here so that fname can be released.
       return tmp;
     }
   }
 #endif
   return "";
 }

 std::string GetAndroidRootSafe(std::string* error_msg) {
 #ifdef _WIN32
   UNUSED(kAndroidRootEnvVar, kAndroidRootDefaultPath, GetRootContainingLibartbase);
   *error_msg = "GetAndroidRootSafe unsupported for Windows.";
   return "";
 #else
   // Prefer ANDROID_ROOT if it's set.
   const char* android_root_from_env = getenv(kAndroidRootEnvVar);
   if (android_root_from_env != nullptr) {
     if (!OS::DirectoryExists(android_root_from_env)) {
       *error_msg =
           StringPrintf("Failed to find %s directory %s", kAndroidRootEnvVar, android_root_from_env);
       return "";
     }
     return android_root_from_env;
   }

   // On host, libartbase is currently installed in "$ANDROID_ROOT/lib"
   // (e.g. something like "$ANDROID_BUILD_TOP/out/host/linux-x86/lib". Use this
   // information to infer the location of the Android Root (on host only).
   //
   // Note that this could change in the future, if we decided to install ART
   // artifacts in a different location, e.g. within an "ART APEX" directory.
   if (!kIsTargetBuild) {
     std::string root_containing_libartbase = GetRootContainingLibartbase();
     if (!root_containing_libartbase.empty()) {
       return root_containing_libartbase;
     }
   }

   // Try the default path.
   if (!OS::DirectoryExists(kAndroidRootDefaultPath)) {
     *error_msg =
         StringPrintf("Failed to find default Android Root directory %s", kAndroidRootDefaultPath);
     return "";
   }
   return kAndroidRootDefaultPath;
 #endif
 }

 std::string GetAndroidRoot() {
   std::string error_msg;
   std::string ret = GetAndroidRootSafe(&error_msg);
   if (ret.empty()) {
     LOG(FATAL) << error_msg;
     UNREACHABLE();
   }
   return ret;
 }


 static const char* GetAndroidDirSafe(const char* env_var,
                                      const char* default_dir,
                                      bool must_exist,
                                      std::string* error_msg) {
   const char* android_dir = getenv(env_var);
   if (android_dir == nullptr) {
     if (!must_exist || OS::DirectoryExists(default_dir)) {
       android_dir = default_dir;
     } else {
       *error_msg = StringPrintf("%s not set and %s does not exist", env_var, default_dir);
       return nullptr;
     }
   }
   if (must_exist && !OS::DirectoryExists(android_dir)) {
     *error_msg = StringPrintf("Failed to find directory %s", android_dir);
     return nullptr;
   }
   return android_dir;
 }

 static const char* GetAndroidDir(const char* env_var, const char* default_dir) {
   std::string error_msg;
   const char* dir = GetAndroidDirSafe(env_var, default_dir, /* must_exist= */ true, &error_msg);
   if (dir != nullptr) {
     return dir;
   } else {
     LOG(FATAL) << error_msg;
     UNREACHABLE();
   }
 }

 static std::string GetArtRootSafe(bool must_exist, /*out*/ std::string* error_msg) {
 #ifdef _WIN32
   UNUSED(kAndroidArtRootEnvVar, kAndroidArtApexDefaultPath, GetRootContainingLibartbase);
   UNUSED(must_exist);
   *error_msg = "GetArtRootSafe unsupported for Windows.";
   return "";
 #else
   // Prefer ANDROID_ART_ROOT if it's set.
   const char* android_art_root_from_env = getenv(kAndroidArtRootEnvVar);
   if (android_art_root_from_env != nullptr) {
     if (must_exist && !OS::DirectoryExists(android_art_root_from_env)) {
       *error_msg = StringPrintf("Failed to find %s directory %s",
                                 kAndroidArtRootEnvVar,
                                 android_art_root_from_env);
       return "";
     }
     return android_art_root_from_env;
   }

   // On target, libartbase is normally installed in
   // "$ANDROID_ART_ROOT/lib(64)" (e.g. something like
   // "/apex/com.android.art/lib(64)". Use this information to infer the
   // location of the ART Root (on target only).
   if (kIsTargetBuild) {
     // *However*, a copy of libartbase may still be installed outside the
     // ART Root on some occasions, as ART target gtests install their binaries
     // and their dependencies under the Android Root, i.e. "/system" (see
     // b/129534335). For that reason, we cannot reliably use
     // `GetRootContainingLibartbase` to find the ART Root. (Note that this is
     // not really a problem in practice, as Android Q devices define
     // ANDROID_ART_ROOT in their default environment, and will instead use
     // the logic above anyway.)
     //
     // TODO(b/129534335): Re-enable this logic when the only instance of
     // libartbase on target is the one from the ART APEX.
     if ((false)) {
       std::string root_containing_libartbase = GetRootContainingLibartbase();
       if (!root_containing_libartbase.empty()) {
         return root_containing_libartbase;
       }
     }
   }

   // Try the default path.
   if (must_exist && !OS::DirectoryExists(kAndroidArtApexDefaultPath)) {
     *error_msg = StringPrintf("Failed to find default ART root directory %s",
                               kAndroidArtApexDefaultPath);
     return "";
   }
   return kAndroidArtApexDefaultPath;
 #endif
 }

 std::string GetArtRootSafe(std::string* error_msg) {
   return GetArtRootSafe(/* must_exist= */ true, error_msg);
 }

 std::string GetArtRoot() {
   std::string error_msg;
   std::string ret = GetArtRootSafe(&error_msg);
   if (ret.empty()) {
     LOG(FATAL) << error_msg;
     UNREACHABLE();
   }
   return ret;
 }

 std::string GetArtBinDir() {
   // Environment variable `ANDROID_ART_ROOT` is defined as
   // `$ANDROID_HOST_OUT/com.android.art` on host. However, host ART binaries are
   // still installed in `$ANDROID_HOST_OUT/bin` (i.e. outside the ART Root). The
   // situation is cleaner on target, where `ANDROID_ART_ROOT` is
   // `$ANDROID_ROOT/apex/com.android.art` and ART binaries are installed in
   // `$ANDROID_ROOT/apex/com.android.art/bin`.
   std::string android_art_root = kIsTargetBuild ? GetArtRoot() : GetAndroidRoot();
   return android_art_root + "/bin";
 }

 std::string GetAndroidDataSafe(std::string* error_msg) {
   const char* android_dir = GetAndroidDirSafe(kAndroidDataEnvVar,
                                               kAndroidDataDefaultPath,
                                               /* must_exist= */ true,
                                               error_msg);
   return (android_dir != nullptr) ? android_dir : "";
 }

 std::string GetAndroidData() {
   return GetAndroidDir(kAndroidDataEnvVar, kAndroidDataDefaultPath);
 }

 std::string GetDefaultBootImageLocation(const std::string& android_root) {
   // Boot image consists of two parts:
   //  - the primary boot image in the ART apex (contains the Core Libraries)
   //  - the boot image extension on the system partition (contains framework libraries)
   return StringPrintf("%s/javalib/boot.art:%s/framework/boot-framework.art",
                       kAndroidArtApexDefaultPath,
                       android_root.c_str());
 }

 std::string GetDefaultBootImageLocation(std::string* error_msg) {
   std::string android_root = GetAndroidRootSafe(error_msg);
   if (android_root.empty()) {
     return "";
   }
   return GetDefaultBootImageLocation(android_root);
 }

 void GetDalvikCache(const char* subdir, const bool create_if_absent, std::string* dalvik_cache,
                     bool* have_android_data, bool* dalvik_cache_exists, bool* is_global_cache) {
 #ifdef _WIN32
   UNUSED(subdir);
   UNUSED(create_if_absent);
   UNUSED(dalvik_cache);
   UNUSED(have_android_data);
   UNUSED(dalvik_cache_exists);
   UNUSED(is_global_cache);
   LOG(FATAL) << "GetDalvikCache unsupported on Windows.";
 #else
   CHECK(subdir != nullptr);
   std::string unused_error_msg;
   std::string android_data = GetAndroidDataSafe(&unused_error_msg);
   if (android_data.empty()) {
     *have_android_data = false;
     *dalvik_cache_exists = false;
     *is_global_cache = false;
     return;
   } else {
     *have_android_data = true;
   }
   const std::string dalvik_cache_root = android_data + "/dalvik-cache";
   *dalvik_cache = dalvik_cache_root + '/' + subdir;
   *dalvik_cache_exists = OS::DirectoryExists(dalvik_cache->c_str());
   *is_global_cache = (android_data == kAndroidDataDefaultPath);
   if (create_if_absent && !*dalvik_cache_exists && !*is_global_cache) {
     // Don't create the system's /data/dalvik-cache/... because it needs special permissions.
     *dalvik_cache_exists = ((mkdir(dalvik_cache_root.c_str(), 0700) == 0 || errno == EEXIST) &&
                             (mkdir(dalvik_cache->c_str(), 0700) == 0 || errno == EEXIST));
   }
 #endif
 }

 std::string GetDalvikCache(const char* subdir) {
   CHECK(subdir != nullptr);
   std::string android_data = GetAndroidData();
   const std::string dalvik_cache_root = android_data + "/dalvik-cache";
   const std::string dalvik_cache = dalvik_cache_root + '/' + subdir;
   if (!OS::DirectoryExists(dalvik_cache.c_str())) {
     // TODO: Check callers. Traditional behavior is to not abort.
     return "";
   }
   return dalvik_cache;
 }

 bool GetDalvikCacheFilename(const char* location, const char* cache_location,
                             std::string* filename, std::string* error_msg) {
   if (location[0] != '/') {
     *error_msg = StringPrintf("Expected path in location to be absolute: %s", location);
     return false;
   }
   std::string cache_file(&location[1]);  // skip leading slash
   if (!android::base::EndsWith(location, ".dex") &&
       !android::base::EndsWith(location, ".art") &&
       !android::base::EndsWith(location, ".oat")) {
     cache_file += "/";
     cache_file += kClassesDex;
   }
   std::replace(cache_file.begin(), cache_file.end(), '/', '@');
   *filename = StringPrintf("%s/%s", cache_location, cache_file.c_str());
   return true;
 }

 std::string GetVdexFilename(const std::string& oat_location) {
   return ReplaceFileExtension(oat_location, "vdex");
 }

 static void InsertIsaDirectory(const InstructionSet isa, std::string* filename) {
   // in = /foo/bar/baz
   // out = /foo/bar/<isa>/baz
   size_t pos = filename->rfind('/');
   CHECK_NE(pos, std::string::npos) << *filename << " " << isa;
   filename->insert(pos, "/", 1);
   filename->insert(pos + 1, GetInstructionSetString(isa));
 }

 std::string GetSystemImageFilename(const char* location, const InstructionSet isa) {
   // location = /system/framework/boot.art
   // filename = /system/framework/<isa>/boot.art
   std::string filename(location);
   InsertIsaDirectory(isa, &filename);
   return filename;
 }

 std::string ReplaceFileExtension(const std::string& filename, const std::string& new_extension) {
   const size_t last_ext = filename.find_last_of("./");
   if (last_ext == std::string::npos || filename[last_ext] != '.') {
     return filename + "." + new_extension;
   } else {
     return filename.substr(0, last_ext + 1) + new_extension;
   }
 }

 bool LocationIsOnArtModule(const char* full_path) {
   std::string unused_error_msg;
   std::string module_path = GetArtRootSafe(/* must_exist= */ kIsTargetBuild, &unused_error_msg);
   if (module_path.empty()) {
     return false;
   }
   return android::base::StartsWith(full_path, module_path);
 }

 static bool StartsWithSlash(const char* str) {
   DCHECK(str != nullptr);
   return str[0] == '/';
 }

 static bool EndsWithSlash(const char* str) {
   DCHECK(str != nullptr);
   size_t len = strlen(str);
   return len > 0 && str[len - 1] == '/';
 }

 // Returns true if `full_path` is located in folder either provided with `env_var`
 // or in `default_path` otherwise. The caller may optionally provide a `subdir`
 // which will be appended to the tested prefix.
 // All of `default_path`, `subdir` and the value of environment variable `env_var`
 // are expected to begin with a slash and not end with one. If this ever changes,
 // the path-building logic should be updated.
 static bool IsLocationOnModule(const char* full_path,
                                const char* env_var,
                                const char* default_path,
                                const char* subdir = nullptr) {
   std::string unused_error_msg;
   const char* module_path = GetAndroidDirSafe(env_var,
                                               default_path,
                                               /* must_exist= */ kIsTargetBuild,
                                               &unused_error_msg);
   if (module_path == nullptr) {
     return false;
   }

   // Build the path which we will check is a prefix of `full_path`. The prefix must
   // end with a slash, so that "/foo/bar" does not match "/foo/barz".
   DCHECK(StartsWithSlash(module_path)) << module_path;
   std::string path_prefix(module_path);
   if (!EndsWithSlash(path_prefix.c_str())) {
     path_prefix.append("/");
   }
   if (subdir != nullptr) {
     // If `subdir` is provided, we assume it is provided without a starting slash
     // but ending with one, e.g. "sub/dir/". `path_prefix` ends with a slash at
     // this point, so we simply append `subdir`.
     DCHECK(!StartsWithSlash(subdir) && EndsWithSlash(subdir)) << subdir;
     path_prefix.append(subdir);
   }

   return android::base::StartsWith(full_path, path_prefix);
 }

 bool LocationIsOnSystemFramework(const char* full_path) {
   return IsLocationOnModule(full_path,
                             kAndroidRootEnvVar,
                             kAndroidRootDefaultPath,
                             /* subdir= */ "framework/");
 }

 bool LocationIsOnConscryptModule(const char* full_path) {
   return IsLocationOnModule(
       full_path, kAndroidConscryptRootEnvVar, kAndroidConscryptApexDefaultPath);
 }

 bool LocationIsOnApex(const char* full_path) {
   return android::base::StartsWith(full_path, kApexDefaultPath);
 }

 bool LocationIsOnSystem(const char* path) {
 #ifdef _WIN32
   UNUSED(path);
   LOG(FATAL) << "LocationIsOnSystem is unsupported on Windows.";
   return false;
 #else
   UniqueCPtr<const char[]> full_path(realpath(path, nullptr));
   return full_path != nullptr &&
       android::base::StartsWith(full_path.get(), GetAndroidRoot().c_str());
 #endif
 }

 bool ArtModuleRootDistinctFromAndroidRoot() {
   std::string error_msg;
   const char* android_root = GetAndroidDirSafe(kAndroidRootEnvVar,
                                                kAndroidRootDefaultPath,
                                                /* must_exist= */ kIsTargetBuild,
                                                &error_msg);
   const char* art_root = GetAndroidDirSafe(kAndroidArtRootEnvVar,
                                            kAndroidArtApexDefaultPath,
                                            /* must_exist= */ kIsTargetBuild,
                                            &error_msg);
   return (android_root != nullptr)
       && (art_root != nullptr)
       && (std::string_view(android_root) != std::string_view(art_root));
 }

 int DupCloexec(int fd) {
 #if defined(__linux__)
   return fcntl(fd, F_DUPFD_CLOEXEC, 0);
 #else
   return dup(fd);
 #endif
 }

 }  // namespace art
	/*
	* Copyright (C) 2011 The Android Open Source Project
	*
	* 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
	*
	* http://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.
	*/

	#include "file_utils.h"

	#include <inttypes.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#ifndef _WIN32
	#include <sys/wait.h>
	#endif
	#include <unistd.h>

	// We need dladdr.
	#if !defined(__APPLE__) && !defined(_WIN32)
	#ifndef _GNU_SOURCE
	#define _GNU_SOURCE
	#define DEFINED_GNU_SOURCE
	#endif
	#include <dlfcn.h>
	#include <libgen.h>
	#ifdef DEFINED_GNU_SOURCE
	#undef _GNU_SOURCE
	#undef DEFINED_GNU_SOURCE
	#endif
	#endif


	#include <memory>

	#include "android-base/stringprintf.h"
	#include "android-base/strings.h"

	#include "base/bit_utils.h"
	#include "base/globals.h"
	#include "base/os.h"
	#include "base/stl_util.h"
	#include "base/unix_file/fd_file.h"

	#if defined(__APPLE__)
	#include <crt_externs.h>
	#include <sys/syscall.h>
	#include "AvailabilityMacros.h" // For MAC_OS_X_VERSION_MAX_ALLOWED
	#endif

	#if defined(__linux__)
	#include <linux/unistd.h>
	#endif

	namespace art {

	using android::base::StringPrintf;

	static constexpr const char* kClassesDex = "classes.dex";
	static constexpr const char* kApexDefaultPath = "/apex/";
	static constexpr const char* kAndroidRootEnvVar = "ANDROID_ROOT";
	static constexpr const char* kAndroidRootDefaultPath = "/system";
	static constexpr const char* kAndroidDataEnvVar = "ANDROID_DATA";
	static constexpr const char* kAndroidDataDefaultPath = "/data";
	static constexpr const char* kAndroidArtRootEnvVar = "ANDROID_ART_ROOT";
	static constexpr const char* kAndroidArtApexDefaultPath = "/apex/com.android.art";
	static constexpr const char* kAndroidConscryptRootEnvVar = "ANDROID_CONSCRYPT_ROOT";
	static constexpr const char* kAndroidConscryptApexDefaultPath = "/apex/com.android.conscrypt";

	// Get the "root" directory containing the "lib" directory where this instance
	// of the libartbase library (which contains `GetRootContainingLibartbase`) is
	// located:
	// - on host this "root" is normally the Android Root (e.g. something like
	// "$ANDROID_BUILD_TOP/out/host/linux-x86/");
	// - on target this "root" is normally the ART Root ("/apex/com.android.art").
	// Return the empty string if that directory cannot be found or if this code is
	// run on Windows or macOS.
	static std::string GetRootContainingLibartbase() {
	#if !defined( _WIN32) && !defined(__APPLE__)
	// Check where libartbase is from, and derive from there.
	Dl_info info;
	if (dladdr(reinterpret_cast<const void>(&GetRootContainingLibartbase), / out */ &info) != 0) {
	// Make a duplicate of the fname so dirname can modify it.
	UniqueCPtr<char> fname(strdup(info.dli_fname));

	char* dir1 = dirname(fname.get()); // This is the lib directory.
	char* dir2 = dirname(dir1); // This is the "root" directory.
	if (OS::DirectoryExists(dir2)) {
	std::string tmp = dir2; // Make a copy here so that fname can be released.
	return tmp;
	}
	}
	#endif
	return "";
	}

	std::string GetAndroidRootSafe(std::string* error_msg) {
	#ifdef _WIN32
	UNUSED(kAndroidRootEnvVar, kAndroidRootDefaultPath, GetRootContainingLibartbase);
	*error_msg = "GetAndroidRootSafe unsupported for Windows.";
	return "";
	#else
	// Prefer ANDROID_ROOT if it's set.
	const char* android_root_from_env = getenv(kAndroidRootEnvVar);
	if (android_root_from_env != nullptr) {
	if (!OS::DirectoryExists(android_root_from_env)) {
	*error_msg =
	StringPrintf("Failed to find %s directory %s", kAndroidRootEnvVar, android_root_from_env);
	return "";
	}
	return android_root_from_env;
	}

	// On host, libartbase is currently installed in "$ANDROID_ROOT/lib"
	// (e.g. something like "$ANDROID_BUILD_TOP/out/host/linux-x86/lib". Use this
	// information to infer the location of the Android Root (on host only).
	//
	// Note that this could change in the future, if we decided to install ART
	// artifacts in a different location, e.g. within an "ART APEX" directory.
	if (!kIsTargetBuild) {
	std::string root_containing_libartbase = GetRootContainingLibartbase();
	if (!root_containing_libartbase.empty()) {
	return root_containing_libartbase;
	}
	}

	// Try the default path.
	if (!OS::DirectoryExists(kAndroidRootDefaultPath)) {
	*error_msg =
	StringPrintf("Failed to find default Android Root directory %s", kAndroidRootDefaultPath);
	return "";
	}
	return kAndroidRootDefaultPath;
	#endif
	}

	std::string GetAndroidRoot() {
	std::string error_msg;
	std::string ret = GetAndroidRootSafe(&error_msg);
	if (ret.empty()) {
	LOG(FATAL) << error_msg;
	UNREACHABLE();
	}
	return ret;
	}


	static const char* GetAndroidDirSafe(const char* env_var,
	const char* default_dir,
	bool must_exist,
	std::string* error_msg) {
	const char* android_dir = getenv(env_var);
	if (android_dir == nullptr) {
	if (!must_exist \|\| OS::DirectoryExists(default_dir)) {
	android_dir = default_dir;
	} else {
	*error_msg = StringPrintf("%s not set and %s does not exist", env_var, default_dir);
	return nullptr;
	}
	}
	if (must_exist && !OS::DirectoryExists(android_dir)) {
	*error_msg = StringPrintf("Failed to find directory %s", android_dir);
	return nullptr;
	}
	return android_dir;
	}

	static const char* GetAndroidDir(const char* env_var, const char* default_dir) {
	std::string error_msg;
	const char* dir = GetAndroidDirSafe(env_var, default_dir, /* must_exist= */ true, &error_msg);
	if (dir != nullptr) {
	return dir;
	} else {
	LOG(FATAL) << error_msg;
	UNREACHABLE();
	}
	}

	static std::string GetArtRootSafe(bool must_exist, /out/ std::string* error_msg) {
	#ifdef _WIN32
	UNUSED(kAndroidArtRootEnvVar, kAndroidArtApexDefaultPath, GetRootContainingLibartbase);
	UNUSED(must_exist);
	*error_msg = "GetArtRootSafe unsupported for Windows.";
	return "";
	#else
	// Prefer ANDROID_ART_ROOT if it's set.
	const char* android_art_root_from_env = getenv(kAndroidArtRootEnvVar);
	if (android_art_root_from_env != nullptr) {
	if (must_exist && !OS::DirectoryExists(android_art_root_from_env)) {
	*error_msg = StringPrintf("Failed to find %s directory %s",
	kAndroidArtRootEnvVar,
	android_art_root_from_env);
	return "";
	}
	return android_art_root_from_env;
	}

	// On target, libartbase is normally installed in
	// "$ANDROID_ART_ROOT/lib(64)" (e.g. something like
	// "/apex/com.android.art/lib(64)". Use this information to infer the
	// location of the ART Root (on target only).
	if (kIsTargetBuild) {
	// However, a copy of libartbase may still be installed outside the
	// ART Root on some occasions, as ART target gtests install their binaries
	// and their dependencies under the Android Root, i.e. "/system" (see
	// b/129534335). For that reason, we cannot reliably use
	// `GetRootContainingLibartbase` to find the ART Root. (Note that this is
	// not really a problem in practice, as Android Q devices define
	// ANDROID_ART_ROOT in their default environment, and will instead use
	// the logic above anyway.)
	//
	// TODO(b/129534335): Re-enable this logic when the only instance of
	// libartbase on target is the one from the ART APEX.
	if ((false)) {
	std::string root_containing_libartbase = GetRootContainingLibartbase();
	if (!root_containing_libartbase.empty()) {
	return root_containing_libartbase;
	}
	}
	}

	// Try the default path.
	if (must_exist && !OS::DirectoryExists(kAndroidArtApexDefaultPath)) {
	*error_msg = StringPrintf("Failed to find default ART root directory %s",
	kAndroidArtApexDefaultPath);
	return "";
	}
	return kAndroidArtApexDefaultPath;
	#endif
	}

	std::string GetArtRootSafe(std::string* error_msg) {
	return GetArtRootSafe(/* must_exist= */ true, error_msg);
	}

	std::string GetArtRoot() {
	std::string error_msg;
	std::string ret = GetArtRootSafe(&error_msg);
	if (ret.empty()) {
	LOG(FATAL) << error_msg;
	UNREACHABLE();
	}
	return ret;
	}

	std::string GetArtBinDir() {
	// Environment variable `ANDROID_ART_ROOT` is defined as
	// `$ANDROID_HOST_OUT/com.android.art` on host. However, host ART binaries are
	// still installed in `$ANDROID_HOST_OUT/bin` (i.e. outside the ART Root). The
	// situation is cleaner on target, where `ANDROID_ART_ROOT` is
	// `$ANDROID_ROOT/apex/com.android.art` and ART binaries are installed in
	// `$ANDROID_ROOT/apex/com.android.art/bin`.
	std::string android_art_root = kIsTargetBuild ? GetArtRoot() : GetAndroidRoot();
	return android_art_root + "/bin";
	}

	std::string GetAndroidDataSafe(std::string* error_msg) {
	const char* android_dir = GetAndroidDirSafe(kAndroidDataEnvVar,
	kAndroidDataDefaultPath,
	/* must_exist= */ true,
	error_msg);
	return (android_dir != nullptr) ? android_dir : "";
	}

	std::string GetAndroidData() {
	return GetAndroidDir(kAndroidDataEnvVar, kAndroidDataDefaultPath);
	}

	std::string GetDefaultBootImageLocation(const std::string& android_root) {
	// Boot image consists of two parts:
	// - the primary boot image in the ART apex (contains the Core Libraries)
	// - the boot image extension on the system partition (contains framework libraries)
	return StringPrintf("%s/javalib/boot.art:%s/framework/boot-framework.art",
	kAndroidArtApexDefaultPath,
	android_root.c_str());
	}

	std::string GetDefaultBootImageLocation(std::string* error_msg) {
	std::string android_root = GetAndroidRootSafe(error_msg);
	if (android_root.empty()) {
	return "";
	}
	return GetDefaultBootImageLocation(android_root);
	}

	void GetDalvikCache(const char* subdir, const bool create_if_absent, std::string* dalvik_cache,
	bool* have_android_data, bool* dalvik_cache_exists, bool* is_global_cache) {
	#ifdef _WIN32
	UNUSED(subdir);
	UNUSED(create_if_absent);
	UNUSED(dalvik_cache);
	UNUSED(have_android_data);
	UNUSED(dalvik_cache_exists);
	UNUSED(is_global_cache);
	LOG(FATAL) << "GetDalvikCache unsupported on Windows.";
	#else
	CHECK(subdir != nullptr);
	std::string unused_error_msg;
	std::string android_data = GetAndroidDataSafe(&unused_error_msg);
	if (android_data.empty()) {
	*have_android_data = false;
	*dalvik_cache_exists = false;
	*is_global_cache = false;
	return;
	} else {
	*have_android_data = true;
	}
	const std::string dalvik_cache_root = android_data + "/dalvik-cache";
	*dalvik_cache = dalvik_cache_root + '/' + subdir;
	*dalvik_cache_exists = OS::DirectoryExists(dalvik_cache->c_str());
	*is_global_cache = (android_data == kAndroidDataDefaultPath);
	if (create_if_absent && !dalvik_cache_exists && !is_global_cache) {
	// Don't create the system's /data/dalvik-cache/... because it needs special permissions.
	*dalvik_cache_exists = ((mkdir(dalvik_cache_root.c_str(), 0700) == 0 \|\| errno == EEXIST) &&
	(mkdir(dalvik_cache->c_str(), 0700) == 0 \|\| errno == EEXIST));
	}
	#endif
	}

	std::string GetDalvikCache(const char* subdir) {
	CHECK(subdir != nullptr);
	std::string android_data = GetAndroidData();
	const std::string dalvik_cache_root = android_data + "/dalvik-cache";
	const std::string dalvik_cache = dalvik_cache_root + '/' + subdir;
	if (!OS::DirectoryExists(dalvik_cache.c_str())) {
	// TODO: Check callers. Traditional behavior is to not abort.
	return "";
	}
	return dalvik_cache;
	}

	bool GetDalvikCacheFilename(const char* location, const char* cache_location,
	std::string* filename, std::string* error_msg) {
	if (location[0] != '/') {
	*error_msg = StringPrintf("Expected path in location to be absolute: %s", location);
	return false;
	}
	std::string cache_file(&location[1]); // skip leading slash
	if (!android::base::EndsWith(location, ".dex") &&
	!android::base::EndsWith(location, ".art") &&
	!android::base::EndsWith(location, ".oat")) {
	cache_file += "/";
	cache_file += kClassesDex;
	}
	std::replace(cache_file.begin(), cache_file.end(), '/', '@');
	*filename = StringPrintf("%s/%s", cache_location, cache_file.c_str());
	return true;
	}

	std::string GetVdexFilename(const std::string& oat_location) {
	return ReplaceFileExtension(oat_location, "vdex");
	}

	static void InsertIsaDirectory(const InstructionSet isa, std::string* filename) {
	// in = /foo/bar/baz
	// out = /foo/bar/<isa>/baz
	size_t pos = filename->rfind('/');
	CHECK_NE(pos, std::string::npos) << *filename << " " << isa;
	filename->insert(pos, "/", 1);
	filename->insert(pos + 1, GetInstructionSetString(isa));
	}

	std::string GetSystemImageFilename(const char* location, const InstructionSet isa) {
	// location = /system/framework/boot.art
	// filename = /system/framework/<isa>/boot.art
	std::string filename(location);
	InsertIsaDirectory(isa, &filename);
	return filename;
	}

	std::string ReplaceFileExtension(const std::string& filename, const std::string& new_extension) {
	const size_t last_ext = filename.find_last_of("./");
	if (last_ext == std::string::npos \|\| filename[last_ext] != '.') {
	return filename + "." + new_extension;
	} else {
	return filename.substr(0, last_ext + 1) + new_extension;
	}
	}

	bool LocationIsOnArtModule(const char* full_path) {
	std::string unused_error_msg;
	std::string module_path = GetArtRootSafe(/* must_exist= */ kIsTargetBuild, &unused_error_msg);
	if (module_path.empty()) {
	return false;
	}
	return android::base::StartsWith(full_path, module_path);
	}

	static bool StartsWithSlash(const char* str) {
	DCHECK(str != nullptr);
	return str[0] == '/';
	}

	static bool EndsWithSlash(const char* str) {
	DCHECK(str != nullptr);
	size_t len = strlen(str);
	return len > 0 && str[len - 1] == '/';
	}

	// Returns true if `full_path` is located in folder either provided with `env_var`
	// or in `default_path` otherwise. The caller may optionally provide a `subdir`
	// which will be appended to the tested prefix.
	// All of `default_path`, `subdir` and the value of environment variable `env_var`
	// are expected to begin with a slash and not end with one. If this ever changes,
	// the path-building logic should be updated.
	static bool IsLocationOnModule(const char* full_path,
	const char* env_var,
	const char* default_path,
	const char* subdir = nullptr) {
	std::string unused_error_msg;
	const char* module_path = GetAndroidDirSafe(env_var,
	default_path,
	/* must_exist= */ kIsTargetBuild,
	&unused_error_msg);
	if (module_path == nullptr) {
	return false;
	}

	// Build the path which we will check is a prefix of `full_path`. The prefix must
	// end with a slash, so that "/foo/bar" does not match "/foo/barz".
	DCHECK(StartsWithSlash(module_path)) << module_path;
	std::string path_prefix(module_path);
	if (!EndsWithSlash(path_prefix.c_str())) {
	path_prefix.append("/");
	}
	if (subdir != nullptr) {
	// If `subdir` is provided, we assume it is provided without a starting slash
	// but ending with one, e.g. "sub/dir/". `path_prefix` ends with a slash at
	// this point, so we simply append `subdir`.
	DCHECK(!StartsWithSlash(subdir) && EndsWithSlash(subdir)) << subdir;
	path_prefix.append(subdir);
	}

	return android::base::StartsWith(full_path, path_prefix);
	}

	bool LocationIsOnSystemFramework(const char* full_path) {
	return IsLocationOnModule(full_path,
	kAndroidRootEnvVar,
	kAndroidRootDefaultPath,
	/* subdir= */ "framework/");
	}

	bool LocationIsOnConscryptModule(const char* full_path) {
	return IsLocationOnModule(
	full_path, kAndroidConscryptRootEnvVar, kAndroidConscryptApexDefaultPath);
	}

	bool LocationIsOnApex(const char* full_path) {
	return android::base::StartsWith(full_path, kApexDefaultPath);
	}

	bool LocationIsOnSystem(const char* path) {
	#ifdef _WIN32
	UNUSED(path);
	LOG(FATAL) << "LocationIsOnSystem is unsupported on Windows.";
	return false;
	#else
	UniqueCPtr<const char[]> full_path(realpath(path, nullptr));
	return full_path != nullptr &&
	android::base::StartsWith(full_path.get(), GetAndroidRoot().c_str());
	#endif
	}

	bool ArtModuleRootDistinctFromAndroidRoot() {
	std::string error_msg;
	const char* android_root = GetAndroidDirSafe(kAndroidRootEnvVar,
	kAndroidRootDefaultPath,
	/* must_exist= */ kIsTargetBuild,
	&error_msg);
	const char* art_root = GetAndroidDirSafe(kAndroidArtRootEnvVar,
	kAndroidArtApexDefaultPath,
	/* must_exist= */ kIsTargetBuild,
	&error_msg);
	return (android_root != nullptr)
	&& (art_root != nullptr)
	&& (std::string_view(android_root) != std::string_view(art_root));
	}

	int DupCloexec(int fd) {
	#if defined(__linux__)
	return fcntl(fd, F_DUPFD_CLOEXEC, 0);
	#else
	return dup(fd);
	#endif
	}

	} // namespace art