From 0d6b8fb0f6ec92aeadaeb54e3cceeff4c6482749 Mon Sep 17 00:00:00 2001
From: Carlo Bramini <carlo_bramini@users.sourceforge.net>
Date: Wed, 11 Feb 2026 21:07:04 +0100
Subject: [PATCH] Add support for CYGWIN

---
 absl/base/attributes.h               | 2 +-
 absl/base/internal/low_level_alloc.h | 4 ++--
 absl/base/internal/sysinfo.cc        | 2 +-
 absl/base/internal/sysinfo.h         | 3 +++
 absl/base/policy_checks.h            | 4 ----
 5 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index cced1709327..5789d9fb159 100644
--- a/absl/base/attributes.h
+++ b/absl/base/attributes.h
@@ -143,7 +143,7 @@
     (!defined(_WIN32) ||                                          \
      (defined(__clang__) && __clang_major__ >= 9 &&               \
       !defined(ABSL_BUILD_DLL) && !defined(ABSL_CONSUME_DLL))) && \
-    !defined(__MINGW32__)
+    !defined(__MINGW32__) && !defined(__CYGWIN__)
 #undef ABSL_ATTRIBUTE_WEAK
 #define ABSL_ATTRIBUTE_WEAK __attribute__((weak))
 #define ABSL_HAVE_ATTRIBUTE_WEAK 1
diff --git a/absl/base/internal/low_level_alloc.h b/absl/base/internal/low_level_alloc.h
index 23218dd5a6f..0da7b42fdfa 100644
--- a/absl/base/internal/low_level_alloc.h
+++ b/absl/base/internal/low_level_alloc.h
@@ -36,7 +36,7 @@
 // LowLevelAlloc.
 #ifdef ABSL_LOW_LEVEL_ALLOC_MISSING
 #error ABSL_LOW_LEVEL_ALLOC_MISSING cannot be directly set
-#elif !defined(ABSL_HAVE_MMAP) && !defined(_WIN32)
+#elif !defined(ABSL_HAVE_MMAP) && !defined(_WIN32) && !defined(__CYGWIN__)
 #define ABSL_LOW_LEVEL_ALLOC_MISSING 1
 #endif
 
@@ -47,7 +47,7 @@
 #ifdef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
 #error ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING cannot be directly set
 #elif defined(_WIN32) || defined(__asmjs__) || defined(__wasm__) || \
-    defined(__hexagon__)
+    defined(__hexagon__) || defined(__CYGWIN__)
 #define ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING 1
 #endif
 
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index a62dd31c22e..d2848b3dce2 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -472,7 +472,7 @@ pid_t GetTID() {
 pid_t GetTID() {
   // `pthread_t` need not be arithmetic per POSIX; platforms where it isn't
   // should be handled above.
-  return static_cast<pid_t>(pthread_self());
+  return reinterpret_cast<pid_t>(pthread_self());
 }
 
 #endif
diff --git a/absl/base/internal/sysinfo.h b/absl/base/internal/sysinfo.h
index 119cf1f0e85..fb1de3bf253 100644
--- a/absl/base/internal/sysinfo.h
+++ b/absl/base/internal/sysinfo.h
@@ -57,6 +57,9 @@ int NumCPUs();
 // return types of GetProcessId() and GetThreadId() are both DWORD, an unsigned
 // 32-bit type.
 using pid_t = uint32_t;
+#elif defined(__CYGWIN__)
+// On CYGWIN, this works on both i686 (deprecated) and x64 targets.
+using pid_t = uintptr_t;
 #endif
 pid_t GetTID();
 
diff --git a/absl/base/policy_checks.h b/absl/base/policy_checks.h
index f84944cfe22..6a74841dda0 100644
--- a/absl/base/policy_checks.h
+++ b/absl/base/policy_checks.h
@@ -38,10 +38,6 @@
 // Operating System Check
 // -----------------------------------------------------------------------------
 
-#if defined(__CYGWIN__)
-#error "Cygwin is not supported."
-#endif
-
 // -----------------------------------------------------------------------------
 // Toolchain Check
 // -----------------------------------------------------------------------------