[libc] Add linux implementations of thrd_create and thrd_join functions.

Reviewers: abrachet, phosek

Differential Revision: https://reviews.llvm.org/D75380

7 files changed, 219 insertions, 0 deletions

diff --git a/libc/src/threads/CMakeLists.txt b/libc/src/threads/CMakeLists.txt
new file mode 100644
index 000000000000..b4bbe81c92ff
--- /dev/null
+++ b/libc/src/threads/CMakeLists.txt
@@ -0,0 +1,3 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()
diff --git a/libc/src/threads/linux/CMakeLists.txt b/libc/src/threads/linux/CMakeLists.txt
new file mode 100644
index 000000000000..809a365a834d
--- /dev/null
+++ b/libc/src/threads/linux/CMakeLists.txt
@@ -0,0 +1,37 @@
+add_header_library(
+  threads_utils
+  HDRS
+    thread_utils.h
+)
+
+add_entrypoint_object(
+  thrd_create
+  SRCS
+    thrd_create.cpp
+  HDRS
+    ../thrd_create.h
+  DEPENDS
+    errno_h
+    linux_syscall_h
+    mmap
+    support_common_h
+    sys_syscall_h
+    threads_h
+    threads_utils
+    __errno_location
+)
+
+add_entrypoint_object(
+  thrd_join
+  SRCS
+    thrd_join.cpp
+  HDRS
+    ../thrd_join.h
+  DEPENDS
+    linux_syscall_h
+    munmap
+    support_common_h
+    sys_syscall_h
+    threads_h
+    threads_utils
+)
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
diff --git a/libc/src/threads/linux/thrd_join.cpp b/libc/src/threads/linux/thrd_join.cpp
new file mode 100644
index 000000000000..7237354f89e9
--- /dev/null
+++ b/libc/src/threads/linux/thrd_join.cpp
@@ -0,0 +1,44 @@
+//===----------- Linux implementation of the thrd_join 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/sys/syscall.h"  // For syscall numbers.
+#include "include/threads.h"      // For thrd_* type definitions.
+#include "src/__support/common.h"
+#include "src/sys/mman/munmap.h"
+#include "src/threads/linux/thread_utils.h"
+
+#include <linux/futex.h> // For futex operations.
+#include <stdatomic.h>   // For atomic_load.
+
+namespace __llvm_libc {
+
+int LLVM_LIBC_ENTRYPOINT(thrd_join)(thrd_t *thread, int *retval) {
+  FutexData *clear_tid_address =
+      reinterpret_cast<FutexData *>(thread->__clear_tid);
+
+  while (atomic_load(clear_tid_address) != 0) {
+    // We cannot do a FUTEX_WAIT_PRIVATE here as the kernel does a
+    // FUTEX_WAKE and not a FUTEX_WAKE_PRIVATE.
+    __llvm_libc::syscall(SYS_futex, clear_tid_address, FUTEX_WAIT,
+                         ThreadParams::ClearTIDValue, nullptr);
+
+    // The kernel should set the value at the clear tid address to zero.
+    // If not, it is a spurious wake and we should continue to wait on
+    // the futex.
+  }
+
+  *retval = thread->__retval;
+
+  if (__llvm_libc::munmap(thread->__stack, thread->__stack_size) == -1)
+    return thrd_error;
+
+  return thrd_success;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/threads/linux/thread_utils.h b/libc/src/threads/linux/thread_utils.h
new file mode 100644
index 000000000000..b6f41b47d81e
--- /dev/null
+++ b/libc/src/threads/linux/thread_utils.h
@@ -0,0 +1,21 @@
+//===--- Linux specific definitions to support mutex operations --*- C++ -*===//
+//
+// 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_SRC_THREADS_LINUX_THREAD_UTILS_H
+#define LLVM_LIBC_SRC_THREADS_LINUX_THREAD_UTILS_H
+
+#include <stdint.h>
+
+using FutexData = _Atomic uint32_t;
+
+struct ThreadParams {
+  static constexpr uintptr_t DefaultStackSize = 1 << 15; // 32 KB
+  static constexpr uint32_t ClearTIDValue = 0xABCD1234;
+};
+
+#endif // LLVM_LIBC_SRC_THREADS_LINUX_THREAD_UTILS_H
diff --git a/libc/src/threads/thrd_create.h b/libc/src/threads/thrd_create.h
new file mode 100644
index 000000000000..311929020905
--- /dev/null
+++ b/libc/src/threads/thrd_create.h
@@ -0,0 +1,20 @@
+//===------- Implementation header for thrd_create function ------ *-C++-* ===//
+//
+// 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_SRC_THREADS_LINUX_THRD_CREATE_H
+#define LLVM_LIBC_SRC_THREADS_LINUX_THRD_CREATE_H
+
+#include "include/threads.h"
+
+namespace __llvm_libc {
+
+int thrd_create(thrd_t *thread, thrd_start_t func, void *arg);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_THREADS_LINUX_THRD_CREATE_H
diff --git a/libc/src/threads/thrd_join.h b/libc/src/threads/thrd_join.h
new file mode 100644
index 000000000000..495b049d5f06
--- /dev/null
+++ b/libc/src/threads/thrd_join.h
@@ -0,0 +1,20 @@
+//===-------- Implementation header for thrd_join function ------- *-C++-* ===//
+//
+// 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_SRC_THREADS_LINUX_THRD_JOIN_H
+#define LLVM_LIBC_SRC_THREADS_LINUX_THRD_JOIN_H
+
+#include "include/threads.h"
+
+namespace __llvm_libc {
+
+int thrd_join(thrd_t *thread, int *retval);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_THREADS_LINUX_THRD_JOIN_H