--- origsrc/libc/src/__support/OSUtil/windows/io.cpp	2025-04-02 08:44:12.000000000 +0900
+++ src/libc/src/__support/OSUtil/windows/io.cpp	2025-04-21 02:00:29.237914500 +0900
@@ -19,7 +19,7 @@ namespace LIBC_NAMESPACE_DECL {
 
 void write_to_stderr(cpp::string_view msg) {
   ::HANDLE stream = ::GetStdHandle(STD_ERROR_HANDLE);
-  ::WriteFile(stream, msg.data(), msg.size(), nullptr, nullptr);
+  ::WriteFile(stream, msg.data(), (DWORD)msg.size(), nullptr, nullptr);
 }
 
 } // namespace LIBC_NAMESPACE_DECL
--- origsrc/libc/src/__support/time/windows/clock_gettime.cpp	2025-04-02 08:44:12.000000000 +0900
+++ src/libc/src/__support/time/windows/clock_gettime.cpp	2025-04-21 02:11:23.878395300 +0900
@@ -18,6 +18,9 @@
 
 #define WIN32_LEAN_AND_MEAN
 #define NOMINMAX
+#ifdef __CYGWIN__
+#include <errno.h>
+#endif
 #include <Windows.h>
 
 namespace LIBC_NAMESPACE_DECL {
--- origsrc/libc/src/__support/time/windows/performance_counter.h	2025-04-02 08:44:12.000000000 +0900
+++ src/libc/src/__support/time/windows/performance_counter.h	2025-04-21 02:11:08.829971800 +0900
@@ -11,6 +11,9 @@
 
 #define WIN32_LEAN_AND_MEAN
 #define NOMINMAX
+#ifdef __CYGWIN__
+#undef fract
+#endif
 #include <Windows.h>
 
 namespace LIBC_NAMESPACE_DECL {
--- origsrc/libc/src/time/windows/clock_getres.cpp	2025-04-02 08:44:12.000000000 +0900
+++ src/libc/src/time/windows/clock_getres.cpp	2025-04-21 02:16:00.167851700 +0900
@@ -23,8 +23,17 @@
 #define NOMINMAX
 #include <Windows.h>
 
+#ifdef __CYGWIN__
+extern "C"
+BOOL GetSystemTimeAdjustmentPrecise(
+  PDWORD64 lpTimeAdjustment,
+  PDWORD64 lpTimeIncrement,
+  PBOOL    lpTimeAdjustmentDisabled
+);
+#else
 // add in dependencies for GetSystemTimeAdjustmentPrecise
 #pragma comment(lib, "mincore.lib")
+#endif
 
 namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(int, clock_getres, (clockid_t id, struct timespec *res)) {
--- origsrc/libc/src/unistd/windows/getentropy.cpp	2025-04-02 08:44:12.000000000 +0900
+++ src/libc/src/unistd/windows/getentropy.cpp	2025-04-21 02:25:49.933088500 +0900
@@ -15,15 +15,25 @@
 #include <Windows.h>
 #include <bcrypt.h>
 #include <ntstatus.h>
+#ifndef __CYGWIN__
 #pragma comment(lib, "bcrypt.lib")
+#endif
 
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(int, getentropy, (void *buffer, size_t length)) {
+#ifdef __CYGWIN__
+  do {
+#else
   __try {
+#endif
     // check the length limit
     if (length > 256)
+#ifdef __CYGWIN__
+      break;
+#else
       __leave;
+#endif
 
     NTSTATUS result = ::BCryptGenRandom(nullptr, static_cast<PUCHAR>(buffer),
                                         static_cast<ULONG>(length),
@@ -32,9 +42,13 @@ LLVM_LIBC_FUNCTION(int, getentropy, (voi
     if (result == STATUS_SUCCESS)
       return 0;
 
+#ifdef __CYGWIN__
+  } while (false);
+#else
   } __except (EXCEPTION_EXECUTE_HANDLER) {
     // no need to handle exceptions specially
   }
+#endif
 
   libc_errno = EIO;
   return -1;