[llvm][Support] Add and use errnoAsErrorCode (#84423)

LLVM is inconsistent about how it converts `errno` to `std::error_code`.
This can cause problems because values outside of `std::errc` compare
differently if one is system and one is generic on POSIX systems.

This is even more of a problem on Windows where use of the system
category is just wrong, as that is for Windows errors, which have a
completely different mapping than POSIX/generic errors. This patch fixes
one instance of this mistake in `JSONTransport.cpp`.

This patch adds `errnoAsErrorCode()` which makes it so people do not
need to think about this issue in the future. It also cleans up a lot of
usage of `errno` in LLVM and Clang.

17 files changed, 94 insertions, 93 deletions

diff --git a/clang-tools-extra/clangd/JSONTransport.cpp b/clang-tools-extra/clangd/JSONTransport.cpp
index 346c7df..3c0e198 100644
--- a/clang-tools-extra/clangd/JSONTransport.cpp
+++ b/clang-tools-extra/clangd/JSONTransport.cpp
@@ -107,8 +107,7 @@ public:
         return error(std::make_error_code(std::errc::operation_canceled),
                      "Got signal, shutting down");
       if (ferror(In))
-        return llvm::errorCodeToError(
-            std::error_code(errno, std::system_category()));
+        return llvm::errorCodeToError(llvm::errnoAsErrorCode());
       if (readRawMessage(JSON)) {
         ThreadCrashReporter ScopedReporter([&JSON]() {
           auto &OS = llvm::errs();
diff --git a/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp b/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
index beca958..2ffbc1a 100644
--- a/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
+++ b/clang/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
@@ -333,8 +333,7 @@ llvm::Expected<std::unique_ptr<DirectoryWatcher>> clang::DirectoryWatcher::creat
   const int InotifyFD = inotify_init1(IN_CLOEXEC);
   if (InotifyFD == -1)
     return llvm::make_error<llvm::StringError>(
-        std::string("inotify_init1() error: ") + strerror(errno),
-        llvm::inconvertibleErrorCode());
+        llvm::errnoAsErrorCode(), std::string(": inotify_init1()"));
 
   const int InotifyWD = inotify_add_watch(
       InotifyFD, Path.str().c_str(),
@@ -346,15 +345,13 @@ llvm::Expected<std::unique_ptr<DirectoryWatcher>> clang::DirectoryWatcher::creat
       );
   if (InotifyWD == -1)
     return llvm::make_error<llvm::StringError>(
-        std::string("inotify_add_watch() error: ") + strerror(errno),
-        llvm::inconvertibleErrorCode());
+        llvm::errnoAsErrorCode(), std::string(": inotify_add_watch()"));
 
   auto InotifyPollingStopper = SemaphorePipe::create();
 
   if (!InotifyPollingStopper)
     return llvm::make_error<llvm::StringError>(
-        std::string("SemaphorePipe::create() error: ") + strerror(errno),
-        llvm::inconvertibleErrorCode());
+        llvm::errnoAsErrorCode(), std::string(": SemaphorePipe::create()"));
 
   return std::make_unique<DirectoryWatcherLinux>(
       Path, Receiver, WaitForInitialSync, InotifyFD, InotifyWD,
diff --git a/llvm/include/llvm/Support/Error.h b/llvm/include/llvm/Support/Error.h
index bb4f38f..894b648 100644
--- a/llvm/include/llvm/Support/Error.h
+++ b/llvm/include/llvm/Support/Error.h
@@ -1180,6 +1180,20 @@ Error errorCodeToError(std::error_code EC);
 /// will trigger a call to abort().
 std::error_code errorToErrorCode(Error Err);
 
+/// Helper to get errno as an std::error_code.
+///
+/// errno should always be represented using the generic category as that's what
+/// both libc++ and libstdc++ do. On POSIX systems you can also represent them
+/// using the system category, however this makes them compare differently for
+/// values outside of those used by `std::errc` if one is generic and the other
+/// is system.
+///
+/// See the libc++ and libstdc++ implementations of `default_error_condition` on
+/// the system category for more details on what the difference is.
+inline std::error_code errnoAsErrorCode() {
+  return std::error_code(errno, std::generic_category());
+}
+
 /// Convert an ErrorOr<T> to an Expected<T>.
 template <typename T> Expected<T> errorOrToExpected(ErrorOr<T> &&EO) {
   if (auto EC = EO.getError())
diff --git a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
index 9cfe547..2c87b34 100644
--- a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
@@ -241,8 +241,7 @@ void SharedMemoryMapper::reserve(size_t NumBytes,
 
         int SharedMemoryFile = shm_open(SharedMemoryName.c_str(), O_RDWR, 0700);
         if (SharedMemoryFile < 0) {
-          return OnReserved(errorCodeToError(
-              std::error_code(errno, std::generic_category())));
+          return OnReserved(errorCodeToError(errnoAsErrorCode()));
         }
 
         // this prevents other processes from accessing it by name
@@ -251,8 +250,7 @@ void SharedMemoryMapper::reserve(size_t NumBytes,
         LocalAddr = mmap(nullptr, NumBytes, PROT_READ | PROT_WRITE, MAP_SHARED,
                          SharedMemoryFile, 0);
         if (LocalAddr == MAP_FAILED) {
-          return OnReserved(errorCodeToError(
-              std::error_code(errno, std::generic_category())));
+          return OnReserved(errorCodeToError(errnoAsErrorCode()));
         }
 
         close(SharedMemoryFile);
@@ -376,8 +374,7 @@ void SharedMemoryMapper::release(ArrayRef<ExecutorAddr> Bases,
 #if defined(LLVM_ON_UNIX)
 
       if (munmap(Reservations[Base].LocalAddr, Reservations[Base].Size) != 0)
-        Err = joinErrors(std::move(Err), errorCodeToError(std::error_code(
-                                             errno, std::generic_category())));
+        Err = joinErrors(std::move(Err), errorCodeToError(errnoAsErrorCode()));
 
 #elif defined(_WIN32)
 
diff --git a/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp b/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
index e8b0e24..6614bee 100644
--- a/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
@@ -62,15 +62,15 @@ ExecutorSharedMemoryMapperService::reserve(uint64_t Size) {
   int SharedMemoryFile =
       shm_open(SharedMemoryName.c_str(), O_RDWR | O_CREAT | O_EXCL, 0700);
   if (SharedMemoryFile < 0)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
 
   // by default size is 0
   if (ftruncate(SharedMemoryFile, Size) < 0)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
 
   void *Addr = mmap(nullptr, Size, PROT_NONE, MAP_SHARED, SharedMemoryFile, 0);
   if (Addr == MAP_FAILED)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
 
   close(SharedMemoryFile);
 
@@ -140,7 +140,7 @@ Expected<ExecutorAddr> ExecutorSharedMemoryMapperService::initialize(
       NativeProt |= PROT_EXEC;
 
     if (mprotect(Segment.Addr.toPtr<void *>(), Segment.Size, NativeProt))
-      return errorCodeToError(std::error_code(errno, std::generic_category()));
+      return errorCodeToError(errnoAsErrorCode());
 
 #elif defined(_WIN32)
 
@@ -240,8 +240,7 @@ Error ExecutorSharedMemoryMapperService::release(
 #if defined(LLVM_ON_UNIX)
 
     if (munmap(Base.toPtr<void *>(), Size) != 0)
-      Err = joinErrors(std::move(Err), errorCodeToError(std::error_code(
-                                           errno, std::generic_category())));
+      Err = joinErrors(std::move(Err), errorCodeToError(errnoAsErrorCode()));
 
 #elif defined(_WIN32)
     (void)Size;
diff --git a/llvm/lib/Object/ArchiveWriter.cpp b/llvm/lib/Object/ArchiveWriter.cpp
index 96e4ec1..be51093 100644
--- a/llvm/lib/Object/ArchiveWriter.cpp
+++ b/llvm/lib/Object/ArchiveWriter.cpp
@@ -926,7 +926,7 @@ Expected<std::string> computeArchiveRelativePath(StringRef From, StringRef To) {
   ErrorOr<SmallString<128>> PathToOrErr = canonicalizePath(To);
   ErrorOr<SmallString<128>> DirFromOrErr = canonicalizePath(From);
   if (!PathToOrErr || !DirFromOrErr)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
 
   const SmallString<128> &PathTo = *PathToOrErr;
   const SmallString<128> &DirFrom = sys::path::parent_path(*DirFromOrErr);
diff --git a/llvm/lib/Support/AutoConvert.cpp b/llvm/lib/Support/AutoConvert.cpp
index 8170e55..74842e9 100644
--- a/llvm/lib/Support/AutoConvert.cpp
+++ b/llvm/lib/Support/AutoConvert.cpp
@@ -82,21 +82,21 @@ int enableAutoConversion(int FD) {
 
 std::error_code llvm::disableAutoConversion(int FD) {
   if (::disableAutoConversion(FD) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
 
 std::error_code llvm::enableAutoConversion(int FD) {
   if (::enableAutoConversion(FD) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
 
 std::error_code llvm::restoreStdHandleAutoConversion(int FD) {
   if (::restoreStdHandleAutoConversion(FD) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
@@ -111,7 +111,7 @@ std::error_code llvm::setFileTag(int FD, int CCSID, bool Text) {
   Tag.ft_rsvflags = 0;
 
   if (fcntl(FD, F_SETTAG, &Tag) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
diff --git a/llvm/lib/Support/LockFileManager.cpp b/llvm/lib/Support/LockFileManager.cpp
index facdc5a..083f8d7 100644
--- a/llvm/lib/Support/LockFileManager.cpp
+++ b/llvm/lib/Support/LockFileManager.cpp
@@ -87,7 +87,7 @@ static std::error_code getHostID(SmallVectorImpl<char> &HostID) {
   struct timespec wait = {1, 0}; // 1 second.
   uuid_t uuid;
   if (gethostuuid(uuid, &wait) != 0)
-    return std::error_code(errno, std::system_category());
+    return errnoAsErrorCode();
 
   uuid_string_t UUIDStr;
   uuid_unparse(uuid, UUIDStr);
diff --git a/llvm/lib/Support/Path.cpp b/llvm/lib/Support/Path.cpp
index acee228..4db9bc8 100644
--- a/llvm/lib/Support/Path.cpp
+++ b/llvm/lib/Support/Path.cpp
@@ -23,7 +23,6 @@
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include <cctype>
-#include <cerrno>
 
 #if !defined(_MSC_VER) && !defined(__MINGW32__)
 #include <unistd.h>
@@ -1010,7 +1009,7 @@ static std::error_code copy_file_internal(int ReadFD, int WriteFD) {
   delete[] Buf;
 
   if (BytesRead < 0 || BytesWritten < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
@@ -1060,7 +1059,7 @@ ErrorOr<MD5::MD5Result> md5_contents(int FD) {
   }
 
   if (BytesRead < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   MD5::MD5Result Result;
   Hash.final(Result);
   return Result;
@@ -1228,7 +1227,7 @@ TempFile::~TempFile() { assert(Done); }
 Error TempFile::discard() {
   Done = true;
   if (FD != -1 && close(FD) == -1) {
-    std::error_code EC = std::error_code(errno, std::generic_category());
+    std::error_code EC = errnoAsErrorCode();
     return errorCodeToError(EC);
   }
   FD = -1;
@@ -1297,10 +1296,8 @@ Error TempFile::keep(const Twine &Name) {
   if (!RenameEC)
     TmpName = "";
 
-  if (close(FD) == -1) {
-    std::error_code EC(errno, std::generic_category());
-    return errorCodeToError(EC);
-  }
+  if (close(FD) == -1)
+    return errorCodeToError(errnoAsErrorCode());
   FD = -1;
 
   return errorCodeToError(RenameEC);
@@ -1319,10 +1316,8 @@ Error TempFile::keep() {
 
   TmpName = "";
 
-  if (close(FD) == -1) {
-    std::error_code EC(errno, std::generic_category());
-    return errorCodeToError(EC);
-  }
+  if (close(FD) == -1)
+    return errorCodeToError(errnoAsErrorCode());
   FD = -1;
 
   return Error::success();
diff --git a/llvm/lib/Support/RandomNumberGenerator.cpp b/llvm/lib/Support/RandomNumberGenerator.cpp
index aea0132..12fe109 100644
--- a/llvm/lib/Support/RandomNumberGenerator.cpp
+++ b/llvm/lib/Support/RandomNumberGenerator.cpp
@@ -18,6 +18,7 @@
 
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/raw_ostream.h"
 #ifdef _WIN32
 #include "llvm/Support/Windows/WindowsSupport.h"
@@ -81,14 +82,14 @@ std::error_code llvm::getRandomBytes(void *Buffer, size_t Size) {
     std::error_code Ret;
     ssize_t BytesRead = read(Fd, Buffer, Size);
     if (BytesRead == -1)
-      Ret = std::error_code(errno, std::system_category());
+      Ret = errnoAsErrorCode();
     else if (BytesRead != static_cast<ssize_t>(Size))
       Ret = std::error_code(EIO, std::system_category());
     if (close(Fd) == -1)
-      Ret = std::error_code(errno, std::system_category());
+      Ret = errnoAsErrorCode();
 
     return Ret;
   }
-  return std::error_code(errno, std::system_category());
+  return errnoAsErrorCode();
 #endif
 }
diff --git a/llvm/lib/Support/Unix/Memory.inc b/llvm/lib/Support/Unix/Memory.inc
index 69bd116..bac208a 100644
--- a/llvm/lib/Support/Unix/Memory.inc
+++ b/llvm/lib/Support/Unix/Memory.inc
@@ -86,7 +86,7 @@ MemoryBlock Memory::allocateMappedMemory(size_t NumBytes,
 #else
   fd = open("/dev/zero", O_RDWR);
   if (fd == -1) {
-    EC = std::error_code(errno, std::generic_category());
+    EC = errnoAsErrorCode();
     return MemoryBlock();
   }
 #endif
@@ -122,7 +122,7 @@ MemoryBlock Memory::allocateMappedMemory(size_t NumBytes,
       return allocateMappedMemory(NumBytes, nullptr, PFlags, EC);
     }
 
-    EC = std::error_code(errno, std::generic_category());
+    EC = errnoAsErrorCode();
 #if !defined(MAP_ANON)
     close(fd);
 #endif
@@ -153,7 +153,7 @@ std::error_code Memory::releaseMappedMemory(MemoryBlock &M) {
     return std::error_code();
 
   if (0 != ::munmap(M.Address, M.AllocatedSize))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   M.Address = nullptr;
   M.AllocatedSize = 0;
@@ -186,7 +186,7 @@ std::error_code Memory::protectMappedMemory(const MemoryBlock &M,
   if (InvalidateCache && !(Protect & PROT_READ)) {
     int Result = ::mprotect((void *)Start, End - Start, Protect | PROT_READ);
     if (Result != 0)
-      return std::error_code(errno, std::generic_category());
+      return errnoAsErrorCode();
 
     Memory::InvalidateInstructionCache(M.Address, M.AllocatedSize);
     InvalidateCache = false;
@@ -196,7 +196,7 @@ std::error_code Memory::protectMappedMemory(const MemoryBlock &M,
   int Result = ::mprotect((void *)Start, End - Start, Protect);
 
   if (Result != 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   if (InvalidateCache)
     Memory::InvalidateInstructionCache(M.Address, M.AllocatedSize);
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
index 9f89d63..968e2c4 100644
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -357,7 +357,7 @@ uint32_t file_status::getLinkCount() const { return fs_st_nlinks; }
 ErrorOr<space_info> disk_space(const Twine &Path) {
   struct STATVFS Vfs;
   if (::STATVFS(const_cast<char *>(Path.str().c_str()), &Vfs))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   auto FrSize = STATVFS_F_FRSIZE(Vfs);
   space_info SpaceInfo;
   SpaceInfo.capacity = static_cast<uint64_t>(Vfs.f_blocks) * FrSize;
@@ -386,7 +386,7 @@ std::error_code current_path(SmallVectorImpl<char> &result) {
       // See if there was a real error.
       if (errno != ENOMEM) {
         result.clear();
-        return std::error_code(errno, std::generic_category());
+        return errnoAsErrorCode();
       }
       // Otherwise there just wasn't enough space.
       result.resize_for_overwrite(result.capacity() * 2);
@@ -403,7 +403,7 @@ std::error_code set_current_path(const Twine &path) {
   StringRef p = path.toNullTerminatedStringRef(path_storage);
 
   if (::chdir(p.begin()) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
@@ -415,7 +415,7 @@ std::error_code create_directory(const Twine &path, bool IgnoreExisting,
 
   if (::mkdir(p.begin(), Perms) == -1) {
     if (errno != EEXIST || !IgnoreExisting)
-      return std::error_code(errno, std::generic_category());
+      return errnoAsErrorCode();
   }
 
   return std::error_code();
@@ -431,7 +431,7 @@ std::error_code create_link(const Twine &to, const Twine &from) {
   StringRef t = to.toNullTerminatedStringRef(to_storage);
 
   if (::symlink(t.begin(), f.begin()) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
@@ -444,7 +444,7 @@ std::error_code create_hard_link(const Twine &to, const Twine &from) {
   StringRef t = to.toNullTerminatedStringRef(to_storage);
 
   if (::link(t.begin(), f.begin()) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
@@ -456,7 +456,7 @@ std::error_code remove(const Twine &path, bool IgnoreNonExisting) {
   struct stat buf;
   if (lstat(p.begin(), &buf) != 0) {
     if (errno != ENOENT || !IgnoreNonExisting)
-      return std::error_code(errno, std::generic_category());
+      return errnoAsErrorCode();
     return std::error_code();
   }
 
@@ -470,7 +470,7 @@ std::error_code remove(const Twine &path, bool IgnoreNonExisting) {
 
   if (::remove(p.begin()) == -1) {
     if (errno != ENOENT || !IgnoreNonExisting)
-      return std::error_code(errno, std::generic_category());
+      return errnoAsErrorCode();
   }
 
   return std::error_code();
@@ -563,7 +563,7 @@ static bool is_local_impl(struct STATVFS &Vfs) {
 std::error_code is_local(const Twine &Path, bool &Result) {
   struct STATVFS Vfs;
   if (::STATVFS(const_cast<char *>(Path.str().c_str()), &Vfs))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   Result = is_local_impl(Vfs);
   return std::error_code();
@@ -572,7 +572,7 @@ std::error_code is_local(const Twine &Path, bool &Result) {
 std::error_code is_local(int FD, bool &Result) {
   struct STATVFS Vfs;
   if (::FSTATVFS(FD, &Vfs))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   Result = is_local_impl(Vfs);
   return std::error_code();
@@ -586,7 +586,7 @@ std::error_code rename(const Twine &from, const Twine &to) {
   StringRef t = to.toNullTerminatedStringRef(to_storage);
 
   if (::rename(f.begin(), t.begin()) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
@@ -595,7 +595,7 @@ std::error_code resize_file(int FD, uint64_t Size) {
   // Use ftruncate as a fallback. It may or may not allocate space. At least on
   // OS X with HFS+ it does.
   if (::ftruncate(FD, Size) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   return std::error_code();
 }
@@ -617,7 +617,7 @@ std::error_code access(const Twine &Path, AccessMode Mode) {
   StringRef P = Path.toNullTerminatedStringRef(PathStorage);
 
   if (::access(P.begin(), convertAccessMode(Mode)) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   if (Mode == AccessMode::Execute) {
     // Don't say that directories are executable.
@@ -726,7 +726,7 @@ static file_type typeForMode(mode_t Mode) {
 static std::error_code fillStatus(int StatRet, const struct stat &Status,
                                   file_status &Result) {
   if (StatRet != 0) {
-    std::error_code EC(errno, std::generic_category());
+    std::error_code EC = errnoAsErrorCode();
     if (EC == errc::no_such_file_or_directory)
       Result = file_status(file_type::file_not_found);
     else
@@ -782,13 +782,13 @@ std::error_code setPermissions(const Twine &Path, perms Permissions) {
   StringRef P = Path.toNullTerminatedStringRef(PathStorage);
 
   if (::chmod(P.begin(), Permissions))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
 std::error_code setPermissions(int FD, perms Permissions) {
   if (::fchmod(FD, Permissions))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
@@ -799,7 +799,7 @@ std::error_code setLastAccessAndModificationTime(int FD, TimePoint<> AccessTime,
   Times[0] = sys::toTimeSpec(AccessTime);
   Times[1] = sys::toTimeSpec(ModificationTime);
   if (::futimens(FD, Times))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 #elif defined(HAVE_FUTIMES)
   timeval Times[2];
@@ -809,7 +809,7 @@ std::error_code setLastAccessAndModificationTime(int FD, TimePoint<> AccessTime,
       sys::toTimeVal(std::chrono::time_point_cast<std::chrono::microseconds>(
           ModificationTime));
   if (::futimes(FD, Times))
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 #elif defined(__MVS__)
   attrib_t Attr;
@@ -819,7 +819,7 @@ std::error_code setLastAccessAndModificationTime(int FD, TimePoint<> AccessTime,
   Attr.att_mtimechg = 1;
   Attr.att_mtime = sys::toTimeT(ModificationTime);
   if (::__fchattr(FD, &Attr, sizeof(Attr)) != 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 #else
 #warning Missing futimes() and futimens()
@@ -858,7 +858,7 @@ std::error_code mapped_file_region::init(int FD, uint64_t Offset,
 
   Mapping = ::mmap(nullptr, Size, prot, flags, FD, Offset);
   if (Mapping == MAP_FAILED)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
@@ -897,7 +897,7 @@ std::error_code detail::directory_iterator_construct(detail::DirIterState &it,
   SmallString<128> path_null(path);
   DIR *directory = ::opendir(path_null.c_str());
   if (!directory)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
   it.IterationHandle = reinterpret_cast<intptr_t>(directory);
   // Add something for replace_filename to replace.
@@ -932,7 +932,7 @@ std::error_code detail::directory_iterator_increment(detail::DirIterState &It) {
   errno = 0;
   dirent *CurDir = ::readdir(reinterpret_cast<DIR *>(It.IterationHandle));
   if (CurDir == nullptr && errno != 0) {
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   } else if (CurDir != nullptr) {
     StringRef Name(CurDir->d_name);
     if ((Name.size() == 1 && Name[0] == '.') ||
@@ -1023,7 +1023,7 @@ std::error_code openFile(const Twine &Name, int &ResultFD,
   // when open is overloaded, such as in Bionic.
   auto Open = [&]() { return ::open(P.begin(), OpenFlags, Mode); };
   if ((ResultFD = sys::RetryAfterSignal(-1, Open)) < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 #ifndef O_CLOEXEC
   if (!(Flags & OF_ChildInherit)) {
     int r = fcntl(ResultFD, F_SETFD, FD_CLOEXEC);
@@ -1087,10 +1087,10 @@ std::error_code openFile(const Twine &Name, int &ResultFD,
    * open().
    */
   if ((Flags & OF_Append) && lseek(ResultFD, 0, SEEK_END) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   struct stat Stat;
   if (fstat(ResultFD, &Stat) == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   if (S_ISREG(Stat.st_mode)) {
     bool DoSetTag = (Access & FA_Write) && (Disp != CD_OpenExisting) &&
                     !Stat.st_tag.ft_txtflag && !Stat.st_tag.ft_ccsid &&
@@ -1190,7 +1190,7 @@ Expected<size_t> readNativeFile(file_t FD, MutableArrayRef<char> Buf) {
 #endif
   ssize_t NumRead = sys::RetryAfterSignal(-1, ::read, FD, Buf.data(), Size);
   if (ssize_t(NumRead) == -1)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
   return NumRead;
 }
 
@@ -1206,11 +1206,11 @@ Expected<size_t> readNativeFileSlice(file_t FD, MutableArrayRef<char> Buf,
       sys::RetryAfterSignal(-1, ::pread, FD, Buf.data(), Size, Offset);
 #else
   if (lseek(FD, Offset, SEEK_SET) == -1)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
   ssize_t NumRead = sys::RetryAfterSignal(-1, ::read, FD, Buf.data(), Size);
 #endif
   if (NumRead == -1)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
   return NumRead;
 }
 
@@ -1243,8 +1243,7 @@ std::error_code lockFile(int FD) {
   Lock.l_len = 0;
   if (::fcntl(FD, F_SETLKW, &Lock) != -1)
     return std::error_code();
-  int Error = errno;
-  return std::error_code(Error, std::generic_category());
+  return errnoAsErrorCode();
 }
 
 std::error_code unlockFile(int FD) {
@@ -1255,7 +1254,7 @@ std::error_code unlockFile(int FD) {
   Lock.l_len = 0;
   if (::fcntl(FD, F_SETLK, &Lock) != -1)
     return std::error_code();
-  return std::error_code(errno, std::generic_category());
+  return errnoAsErrorCode();
 }
 
 std::error_code closeFile(file_t &F) {
@@ -1321,7 +1320,7 @@ std::error_code real_path(const Twine &path, SmallVectorImpl<char> &dest,
   StringRef P = path.toNullTerminatedStringRef(Storage);
   char Buffer[PATH_MAX];
   if (::realpath(P.begin(), Buffer) == nullptr)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   dest.append(Buffer, Buffer + strlen(Buffer));
   return std::error_code();
 }
@@ -1330,7 +1329,7 @@ std::error_code changeFileOwnership(int FD, uint32_t Owner, uint32_t Group) {
   auto FChown = [&]() { return ::fchown(FD, Owner, Group); };
   // Retry if fchown call fails due to interruption.
   if ((sys::RetryAfterSignal(-1, FChown)) < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
@@ -1513,7 +1512,7 @@ std::error_code copy_file(const Twine &From, const Twine &To) {
 #endif
   if (!copyfile(FromS.c_str(), ToS.c_str(), /*State=*/NULL, COPYFILE_DATA))
     return std::error_code();
-  return std::error_code(errno, std::generic_category());
+  return errnoAsErrorCode();
 }
 #endif // __APPLE__
 
diff --git a/llvm/lib/Support/Unix/Process.inc b/llvm/lib/Support/Unix/Process.inc
index ecba37d..ae90924 100644
--- a/llvm/lib/Support/Unix/Process.inc
+++ b/llvm/lib/Support/Unix/Process.inc
@@ -86,7 +86,7 @@ Expected<unsigned> Process::getPageSize() {
 #error Cannot get the page size on this machine
 #endif
   if (page_size == -1)
-    return errorCodeToError(std::error_code(errno, std::generic_category()));
+    return errorCodeToError(errnoAsErrorCode());
 
   return static_cast<unsigned>(page_size);
 }
@@ -235,7 +235,7 @@ std::error_code Process::FixupStandardFileDescriptors() {
       assert(errno && "expected errno to be set if fstat failed!");
       // fstat should return EBADF if the file descriptor is closed.
       if (errno != EBADF)
-        return std::error_code(errno, std::generic_category());
+        return errnoAsErrorCode();
     }
     // if fstat succeeds, move on to the next FD.
     if (!errno)
@@ -247,13 +247,13 @@ std::error_code Process::FixupStandardFileDescriptors() {
       // RetryAfterSignal when open is overloaded, such as in Bionic.
       auto Open = [&]() { return ::open("/dev/null", O_RDWR); };
       if ((NullFD = RetryAfterSignal(-1, Open)) < 0)
-        return std::error_code(errno, std::generic_category());
+        return errnoAsErrorCode();
     }
 
     if (NullFD == StandardFD)
       FDC.keepOpen();
     else if (dup2(NullFD, StandardFD) < 0)
-      return std::error_code(errno, std::generic_category());
+      return errnoAsErrorCode();
   }
   return std::error_code();
 }
@@ -262,7 +262,7 @@ std::error_code Process::SafelyCloseFileDescriptor(int FD) {
   // Create a signal set filled with *all* signals.
   sigset_t FullSet, SavedSet;
   if (sigfillset(&FullSet) < 0 || sigfillset(&SavedSet) < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 
     // Atomically swap our current signal mask with a full mask.
 #if LLVM_ENABLE_THREADS
@@ -270,7 +270,7 @@ std::error_code Process::SafelyCloseFileDescriptor(int FD) {
     return std::error_code(EC, std::generic_category());
 #else
   if (sigprocmask(SIG_SETMASK, &FullSet, &SavedSet) < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
 #endif
   // Attempt to close the file descriptor.
   // We need to save the error, if one occurs, because our subsequent call to
diff --git a/llvm/lib/Support/Windows/Process.inc b/llvm/lib/Support/Windows/Process.inc
index 6b4b723..34d294b 100644
--- a/llvm/lib/Support/Windows/Process.inc
+++ b/llvm/lib/Support/Windows/Process.inc
@@ -276,7 +276,7 @@ std::error_code Process::FixupStandardFileDescriptors() {
 
 std::error_code Process::SafelyCloseFileDescriptor(int FD) {
   if (::close(FD) < 0)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
diff --git a/llvm/lib/Support/Windows/Program.inc b/llvm/lib/Support/Windows/Program.inc
index d98d55f..799af55 100644
--- a/llvm/lib/Support/Windows/Program.inc
+++ b/llvm/lib/Support/Windows/Program.inc
@@ -506,14 +506,14 @@ std::error_code llvm::sys::ChangeStdoutMode(sys::fs::OpenFlags Flags) {
 std::error_code sys::ChangeStdinToBinary() {
   int result = _setmode(_fileno(stdin), _O_BINARY);
   if (result == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
 std::error_code sys::ChangeStdoutToBinary() {
   int result = _setmode(_fileno(stdout), _O_BINARY);
   if (result == -1)
-    return std::error_code(errno, std::generic_category());
+    return errnoAsErrorCode();
   return std::error_code();
 }
 
diff --git a/llvm/lib/Support/raw_ostream.cpp b/llvm/lib/Support/raw_ostream.cpp
index c7064d2..8cb7b5a 100644
--- a/llvm/lib/Support/raw_ostream.cpp
+++ b/llvm/lib/Support/raw_ostream.cpp
@@ -794,7 +794,7 @@ void raw_fd_ostream::write_impl(const char *Ptr, size_t Size) {
       }
 #endif
       // Otherwise it's a non-recoverable error. Note it and quit.
-      error_detected(std::error_code(errno, std::generic_category()));
+      error_detected(errnoAsErrorCode());
       break;
     }
 
@@ -824,7 +824,7 @@ uint64_t raw_fd_ostream::seek(uint64_t off) {
   pos = ::lseek(FD, off, SEEK_SET);
 #endif
   if (pos == (uint64_t)-1)
-    error_detected(std::error_code(errno, std::generic_category()));
+    error_detected(errnoAsErrorCode());
   return pos;
 }
 
@@ -946,7 +946,7 @@ ssize_t raw_fd_stream::read(char *Ptr, size_t Size) {
   if (Ret >= 0)
     inc_pos(Ret);
   else
-    error_detected(std::error_code(errno, std::generic_category()));
+    error_detected(errnoAsErrorCode());
   return Ret;
 }
 
diff --git a/llvm/lib/Support/raw_socket_stream.cpp b/llvm/lib/Support/raw_socket_stream.cpp
index a65865bc..afb0ed1 100644
--- a/llvm/lib/Support/raw_socket_stream.cpp
+++ b/llvm/lib/Support/raw_socket_stream.cpp
@@ -52,7 +52,7 @@ static std::error_code getLastSocketErrorCode() {
 #ifdef _WIN32
   return std::error_code(::WSAGetLastError(), std::system_category());
 #else
-  return std::error_code(errno, std::system_category());
+  return errnoAsErrorCode();
 #endif
 }