5 files changed, 40 insertions, 0 deletions
diff --git a/libc/include/CMakeLists.txt b/libc/include/CMakeLists.txt
index a8aac4cfbd31..e8db6b72df70 100644
--- a/libc/include/CMakeLists.txt
+++ b/libc/include/CMakeLists.txt
@@ -188,6 +188,8 @@ add_gen_header(
     .llvm-libc-types.pthread_key_t
     .llvm-libc-types.pthread_mutex_t
     .llvm-libc-types.pthread_mutexattr_t
+    .llvm-libc-types.pthread_once_t
+    .llvm-libc-types.__pthread_once_func_t
     .llvm-libc-types.pthread_t
 )
 
diff --git a/libc/include/llvm-libc-types/CMakeLists.txt b/libc/include/llvm-libc-types/CMakeLists.txt
index 5fde05a3665a..5f0a5796042c 100644
--- a/libc/include/llvm-libc-types/CMakeLists.txt
+++ b/libc/include/llvm-libc-types/CMakeLists.txt
@@ -4,6 +4,7 @@ add_header(__bsearchcompare_t HDR __bsearchcompare_t.h)
 add_header(__call_once_func_t HDR __call_once_func_t.h)
 add_header(__futex_word HDR __futex_word.h)
 add_header(__mutex_type HDR __mutex_type.h DEPENDS .__futex_word)
+add_header(__pthread_once_func_t HDR __pthread_once_func_t.h)
 add_header(__pthread_start_t HDR __pthread_start_t.h)
 add_header(__pthread_tss_dtor_t HDR __pthread_tss_dtor_t.h)
 add_header(__qsortcompare_t HDR __qsortcompare_t.h)
@@ -38,6 +39,7 @@ add_header(pthread_key_t HDR pthread_key_t.h)
 add_header(pthread_mutex_t HDR pthread_mutex_t.h DEPENDS .__futex_word .__mutex_type)
 add_header(pthread_t HDR pthread_t.h DEPENDS .__thread_type)
 add_header(pthread_mutexattr_t HDR pthread_mutexattr_t.h)
+add_header(pthread_once_t HDR pthread_once_t.h DEPENDS .__futex_word)
 add_header(rlim_t HDR rlim_t.h)
 add_header(struct_rlimit HDR struct_rlimit.h DEPENDS .rlim_t)
 add_header(ssize_t HDR ssize_t.h)
diff --git a/libc/include/llvm-libc-types/__pthread_once_func_t.h b/libc/include/llvm-libc-types/__pthread_once_func_t.h
new file mode 100644
index 000000000000..5ace5cb7f151
--- /dev/null
+++ b/libc/include/llvm-libc-types/__pthread_once_func_t.h
@@ -0,0 +1,14 @@
+//===-- Definition of __pthread_once_func_t type --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __LLVM_LIBC_TYPES_PTHREAD_ONCE_FUNC_T_H__
+#define __LLVM_LIBC_TYPES_PTHREAD_ONCE_FUNC_T_H__
+
+typedef void (*__pthread_once_func_t)(void);
+
+#endif // __LLVM_LIBC_TYPES_PTHREAD_ONCE_FUNC_T_H__
diff --git a/libc/include/llvm-libc-types/pthread_once_t.h b/libc/include/llvm-libc-types/pthread_once_t.h
new file mode 100644
index 000000000000..be5c139d0c0e
--- /dev/null
+++ b/libc/include/llvm-libc-types/pthread_once_t.h
@@ -0,0 +1,20 @@
+//===-- Definition of pthread_once_t type ---------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef __LLVM_LIBC_TYPES_PTHREAD_ONCE_T_H__
+#define __LLVM_LIBC_TYPES_PTHREAD_ONCE_T_H__
+
+#include <llvm-libc-types/__futex_word.h>
+
+#ifdef __unix__
+typedef __futex_word pthread_once_t;
+#else
+#error "Once flag type not defined for the target platform."
+#endif
+
+#endif // __LLVM_LIBC_TYPES_PTHREAD_ONCE_T_H__
diff --git a/libc/include/pthread.h.def b/libc/include/pthread.h.def
index 60f257e7078d..18352c053938 100644
--- a/libc/include/pthread.h.def
+++ b/libc/include/pthread.h.def
@@ -13,6 +13,8 @@
 
 #define PTHREAD_STACK_MIN (1 << 14) // 16KB
 
+#define PTHREAD_ONCE_INIT {0}
+
 enum {
   PTHREAD_CREATE_JOINABLE = 0x0,
   PTHREAD_CREATE_DETACHED = 0x1,