1 files changed, 74 insertions, 0 deletions
diff --git a/libc/src/threads/linux/thrd_create.cpp b/libc/src/threads/linux/thrd_create.cpp
new file mode 100644
index 000000000000..650c38cab924
--- /dev/null
+++ b/libc/src/threads/linux/thrd_create.cpp
@@ -0,0 +1,74 @@
+//===---------- Linux implementation of the thrd_create function ----------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "config/linux/syscall.h" // For syscall function.
+#include "include/errno.h"        // For E* error values.
+#include "include/sys/mman.h"     // For PROT_* and MAP_* definitions.
+#include "include/sys/syscall.h"  // For syscall numbers.
+#include "include/threads.h"      // For thrd_* type definitions.
+#include "src/__support/common.h"
+#include "src/errno/llvmlibc_errno.h"
+#include "src/sys/mman/mmap.h"
+#include "src/sys/mman/munmap.h"
+#include "src/threads/linux/thread_utils.h"
+
+#include <linux/futex.h> // For futex operations.
+#include <linux/sched.h> // For CLONE_* flags.
+#include <stdint.h>
+
+namespace __llvm_libc {
+
+static void start_thread(thrd_t *thread, thrd_start_t func, void *arg) {
+  __llvm_libc::syscall(SYS_exit, thread->__retval = func(arg));
+}
+
+int LLVM_LIBC_ENTRYPOINT(thrd_create)(thrd_t *thread, thrd_start_t func,
+                                      void *arg) {
+  unsigned clone_flags =
+      CLONE_VM        // Share the memory space with the parent.
+      | CLONE_FS      // Share the file system with the parent.
+      | CLONE_FILES   // Share the files with the parent.
+      | CLONE_SIGHAND // Share the signal handlers with the parent.
+      | CLONE_THREAD  // Same thread group as the parent.
+      | CLONE_SYSVSEM // Share a single list of System V semaphore adjustment
+                      // values
+      | CLONE_PARENT_SETTID   // Set child thread ID in |ptid| of the parent.
+      | CLONE_CHILD_CLEARTID; // Let the kernel clear the tid address and futex
+                              // wake the joining thread.
+  // TODO: Add the CLONE_SETTLS flag and setup the TLS area correctly when
+  // making the clone syscall.
+
+  void *stack = __llvm_libc::mmap(nullptr, ThreadParams::DefaultStackSize,
+                                  PROT_READ | PROT_WRITE,
+                                  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  if (stack == MAP_FAILED)
+    return llvmlibc_errno == ENOMEM ? thrd_nomem : thrd_error;
+
+  thread->__stack = stack;
+  thread->__stack_size = ThreadParams::DefaultStackSize;
+  thread->__retval = -1;
+  FutexData *clear_tid_address =
+      reinterpret_cast<FutexData *>(thread->__clear_tid);
+  *clear_tid_address = ThreadParams::ClearTIDValue;
+
+  long clone_result = __llvm_libc::syscall(
+      SYS_clone, clone_flags,
+      reinterpret_cast<uintptr_t>(stack) + ThreadParams::DefaultStackSize - 1,
+      &thread->__tid, clear_tid_address, 0);
+
+  if (clone_result == 0) {
+    start_thread(thread, func, arg);
+  } else if (clone_result < 0) {
+    int error_val = -clone_result;
+    return error_val == ENOMEM ? thrd_nomem : thrd_error;
+  }
+
+  return thrd_success;
+}
+
+} // namespace __llvm_libc