diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -503,6 +503,9 @@
   if (NOT CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     append("-Wa,-mbig-obj" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
   endif()
+elseif(SERENITYOS)
+  # SerenityOS sets a very low default stack size value, so increase it to 4MB manually.
+  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-z,stack-size=4194304")
 endif()
 
 option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
diff --git a/llvm/include/llvm/ADT/bit.h b/llvm/include/llvm/ADT/bit.h
--- a/llvm/include/llvm/ADT/bit.h
+++ b/llvm/include/llvm/ADT/bit.h
@@ -28,7 +28,8 @@
 #endif
 
 #if defined(__linux__) || defined(__GNU__) || defined(__HAIKU__) ||            \
-    defined(__Fuchsia__) || defined(__EMSCRIPTEN__) || defined(__OpenBSD__)
+    defined(__Fuchsia__) || defined(__EMSCRIPTEN__) || defined(__OpenBSD__) || \
+    defined(__serenity__)
 #include <endian.h>
 #elif defined(_AIX)
 #include <sys/machine.h>
diff --git a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
--- a/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/MemoryMapper.cpp
@@ -215,7 +215,8 @@
 
 void SharedMemoryMapper::reserve(size_t NumBytes,
                                  OnReservedFunction OnReserved) {
-#if (defined(LLVM_ON_UNIX) && !defined(__ANDROID__)) || defined(_WIN32)
+#if (defined(LLVM_ON_UNIX) && !(defined(__ANDROID__) || defined(__serenity__))) \
+    || defined(_WIN32)
 
   EPC.callSPSWrapperAsync<
       rt::SPSExecutorSharedMemoryMapperServiceReserveSignature>(
diff --git a/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp b/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
--- a/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.cpp
@@ -47,7 +47,8 @@
 
 Expected<std::pair<ExecutorAddr, std::string>>
 ExecutorSharedMemoryMapperService::reserve(uint64_t Size) {
-#if (defined(LLVM_ON_UNIX) && !defined(__ANDROID__)) || defined(_WIN32)
+#if (defined(LLVM_ON_UNIX) && !(defined(__ANDROID__) || defined(__serenity__))) \
+    || defined(_WIN32)
 
 #if defined(LLVM_ON_UNIX)
 
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -112,7 +112,7 @@
 #endif
 
 #if defined(__NetBSD__) || defined(__DragonFly__) || defined(__GNU__) ||       \
-    defined(__MVS__)
+    defined(__MVS__) || defined(__serenity__)
 #define STATVFS_F_FLAG(vfs) (vfs).f_flag
 #else
 #define STATVFS_F_FLAG(vfs) (vfs).f_flags
@@ -511,6 +511,9 @@
 #elif defined(__HAIKU__)
   // Haiku doesn't expose this information.
   return false;
+#elif defined(__serenity__)
+  // Serenity doesn't yet support remote filesystem mounts.
+  return false;
 #elif defined(__sun)
   // statvfs::f_basetype contains a null-terminated FSType name of the mounted
   // target
diff --git a/llvm/lib/Support/Unix/Program.inc b/llvm/lib/Support/Unix/Program.inc
--- a/llvm/lib/Support/Unix/Program.inc
+++ b/llvm/lib/Support/Unix/Program.inc
@@ -342,7 +342,7 @@
 
 #if defined(_AIX)
 static pid_t(wait4)(pid_t pid, int *status, int options, struct rusage *usage);
-#elif !defined(__Fuchsia__)
+#elif !defined(__Fuchsia__) && !defined(__serenity__)
 using ::wait4;
 #endif
 
@@ -383,6 +383,13 @@
 }
 #endif
 
+#ifdef __serenity__
+pid_t (llvm::sys::wait4)(pid_t pid, int *status, int options,
+                         struct rusage*) {
+  return ::waitpid(pid, status, options);
+}
+#endif
+
 ProcessInfo llvm::sys::Wait(const ProcessInfo &PI,
                             std::optional<unsigned> SecondsToWait,
                             std::string *ErrMsg,