[libc-commits] [libc] reland "[libc] implement cached process/thread identity (#98989)" (PR #99765)
via libc-commits
libc-commits at lists.llvm.org
Sat Jul 20 08:05:40 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libc
Author: Schrodinger ZHU Yifan (SchrodingerZhu)
<details>
<summary>Changes</summary>
Reverts llvm/llvm-project#<!-- -->99559
---
Patch is 28.20 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/99765.diff
30 Files Affected:
- (modified) libc/config/config.json (+10)
- (modified) libc/config/linux/aarch64/entrypoints.txt (+1)
- (modified) libc/config/linux/riscv/entrypoints.txt (+1)
- (modified) libc/config/linux/x86_64/entrypoints.txt (+1)
- (modified) libc/docs/configure.rst (+3)
- (modified) libc/docs/dev/undefined_behavior.rst (+23)
- (modified) libc/spec/posix.td (+5-10)
- (modified) libc/src/__support/OSUtil/CMakeLists.txt (+17)
- (modified) libc/src/__support/OSUtil/linux/CMakeLists.txt (+13)
- (added) libc/src/__support/OSUtil/linux/pid.cpp (+20)
- (added) libc/src/__support/OSUtil/pid.h (+41)
- (modified) libc/src/__support/threads/CMakeLists.txt (+27)
- (modified) libc/src/__support/threads/linux/CMakeLists.txt (+1)
- (modified) libc/src/__support/threads/linux/rwlock.h (+4-5)
- (modified) libc/src/__support/threads/linux/thread.cpp (+2)
- (modified) libc/src/__support/threads/thread.h (+26-1)
- (added) libc/src/__support/threads/tid.h (+34)
- (modified) libc/src/unistd/CMakeLists.txt (+10)
- (modified) libc/src/unistd/getpid.h (+2-2)
- (added) libc/src/unistd/gettid.cpp (+17)
- (added) libc/src/unistd/gettid.h (+21)
- (modified) libc/src/unistd/linux/CMakeLists.txt (+2-2)
- (modified) libc/src/unistd/linux/fork.cpp (+22-10)
- (modified) libc/src/unistd/linux/getpid.cpp (+2-9)
- (modified) libc/startup/linux/CMakeLists.txt (+1)
- (modified) libc/startup/linux/do_start.cpp (+5)
- (modified) libc/test/integration/src/unistd/CMakeLists.txt (+4)
- (modified) libc/test/integration/src/unistd/fork_test.cpp (+23-1)
- (modified) libc/test/src/unistd/CMakeLists.txt (+10)
- (added) libc/test/src/unistd/gettid_test.cpp (+15)
``````````diff
diff --git a/libc/config/config.json b/libc/config/config.json
index 94bfed894c173..0fc88e2b8dbd5 100644
--- a/libc/config/config.json
+++ b/libc/config/config.json
@@ -75,6 +75,16 @@
"LIBC_CONF_FREELIST_MALLOC_BUFFER_SIZE": {
"value": 1073741824,
"doc": "Default size for the constinit freelist buffer used for the freelist malloc implementation (default 1o 1GB)."
+ },
+ },
+ "unistd": {
+ "LIBC_CONF_ENABLE_TID_CACHE": {
+ "value": true,
+ "doc": "Enable caching mechanism for gettid to avoid syscall (only effective in fullbuild mode, default to true). Please refer to Undefined Behavior documentation for implications."
+ },
+ "LIBC_CONF_ENABLE_PID_CACHE": {
+ "value": true,
+ "doc": "Enable caching mechanism for getpid to avoid syscall (default to true). Please refer to Undefined Behavior documentation for implications."
}
},
"math": {
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index e2f6bd74bb694..8afd3fb67197e 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -297,6 +297,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.unistd.geteuid
libc.src.unistd.getpid
libc.src.unistd.getppid
+ libc.src.unistd.gettid
libc.src.unistd.getuid
libc.src.unistd.isatty
libc.src.unistd.link
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index 33dd8d06173b2..f61936b758bd9 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -296,6 +296,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.unistd.geteuid
libc.src.unistd.getpid
libc.src.unistd.getppid
+ libc.src.unistd.gettid
libc.src.unistd.getuid
libc.src.unistd.isatty
libc.src.unistd.link
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 7309e95644c74..f2029da83ee71 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -315,6 +315,7 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.unistd.geteuid
libc.src.unistd.getpid
libc.src.unistd.getppid
+ libc.src.unistd.gettid
libc.src.unistd.getuid
libc.src.unistd.isatty
libc.src.unistd.link
diff --git a/libc/docs/configure.rst b/libc/docs/configure.rst
index dfb35f6a6611a..5c55e4ab0f181 100644
--- a/libc/docs/configure.rst
+++ b/libc/docs/configure.rst
@@ -52,3 +52,6 @@ to learn about the defaults for your platform and target.
* **"string" options**
- ``LIBC_CONF_MEMSET_X86_USE_SOFTWARE_PREFETCHING``: Inserts prefetch for write instructions (PREFETCHW) for memset on x86 to recover performance when hardware prefetcher is disabled.
- ``LIBC_CONF_STRING_UNSAFE_WIDE_READ``: Read more than a byte at a time to perform byte-string operations like strlen.
+* **"unistd" options**
+ - ``LIBC_CONF_ENABLE_PID_CACHE``: Enable caching mechanism for getpid to avoid syscall (default to true). Please refer to Undefined Behavior documentation for implications.
+ - ``LIBC_CONF_ENABLE_TID_CACHE``: Enable caching mechanism for gettid to avoid syscall (only effective in fullbuild mode, default to true). Please refer to Undefined Behavior documentation for implications.
diff --git a/libc/docs/dev/undefined_behavior.rst b/libc/docs/dev/undefined_behavior.rst
index 3faae3134ce2a..b712780222aa3 100644
--- a/libc/docs/dev/undefined_behavior.rst
+++ b/libc/docs/dev/undefined_behavior.rst
@@ -93,3 +93,26 @@ direction in this case.
Non-const Constant Return Values
--------------------------------
Some libc functions, like ``dlerror()``, return ``char *`` instead of ``const char *`` and then tell the caller they promise not to to modify this value. Any modification of this value is undefined behavior.
+
+Cached ``getpid/gettid``
+------------------------
+Since version ``2.25``, glibc removes its cache mechanism for ``getpid/gettid``
+(See the history section in https://man7.org/linux/man-pages/man2/getpid.2.html).
+LLVM's libc still implements the cache as it is useful for fast deadlock detection.
+The cache mechanism is also implemented in MUSL and bionic. The tid/pid cache can
+be disabled by setting ``LIBC_CONF_ENABLE_TID_CACHE`` and ``LIBC_CONF_ENABLE_PID_CACHE``
+to ``false`` respectively.
+
+Unwrapped ``SYS_clone/SYS_fork/SYS_vfork``
+------------------------------------------
+It is highly discouraged to use unwrapped ``SYS_clone/SYS_fork/SYS_vfork``.
+First, calling such syscalls without provided libc wrappers ignores
+all the ``pthread_atfork`` entries as libc can no longer detect the ``fork``.
+Second, libc relies on the ``fork/clone`` wrappers to correctly maintain cache for
+process id and thread id, and other important process-specific states such as the list
+of robust mutexes. Third, even if the user is to call ``exec*`` functions immediately,
+there can still be other unexpected issues. For instance, there can be signal handlers
+inherited from parent process triggered inside the instruction window between ``fork``
+and ``exec*``. As libc failed to maintain its internal states correctly, even though the
+functions used inside the signal handlers are marked as ``async-signal-safe`` (such as
+``getpid``), they will still return wrong values or lead to other even worse situations.
diff --git a/libc/spec/posix.td b/libc/spec/posix.td
index 1878b1ee2ae41..48f743dff4e6f 100644
--- a/libc/spec/posix.td
+++ b/libc/spec/posix.td
@@ -546,6 +546,11 @@ def POSIX : StandardSpec<"POSIX"> {
RetValSpec<PidT>,
[ArgSpec<VoidType>]
>,
+ FunctionSpec<
+ "gettid",
+ RetValSpec<PidT>,
+ [ArgSpec<VoidType>]
+ >,
FunctionSpec<
"getuid",
RetValSpec<UidT>,
@@ -601,16 +606,6 @@ def POSIX : StandardSpec<"POSIX"> {
RetValSpec<IntType>,
[ArgSpec<ConstCharPtr>]
>,
- FunctionSpec<
- "getpid",
- RetValSpec<IntType>,
- [ArgSpec<VoidType>]
- >,
- FunctionSpec<
- "getppid",
- RetValSpec<IntType>,
- [ArgSpec<VoidType>]
- >,
FunctionSpec<
"link",
RetValSpec<IntType>,
diff --git a/libc/src/__support/OSUtil/CMakeLists.txt b/libc/src/__support/OSUtil/CMakeLists.txt
index 94d1042ccbb4a..517f888178718 100644
--- a/libc/src/__support/OSUtil/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/CMakeLists.txt
@@ -15,3 +15,20 @@ add_object_library(
DEPENDS
${target_os_util}
)
+
+if (LIBC_CONF_ENABLE_PID_CACHE)
+ set(libc_copt_enable_pid_cache 1)
+else()
+ set(libc_copt_enable_pid_cache 0)
+endif()
+
+if(TARGET libc.src.__support.OSUtil.${LIBC_TARGET_OS}.pid)
+ add_object_library(
+ pid
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.pid
+ COMPILE_OPTIONS
+ -DLIBC_COPT_ENABLE_PID_CACHE=${libc_copt_enable_pid_cache}
+ )
+endif()
diff --git a/libc/src/__support/OSUtil/linux/CMakeLists.txt b/libc/src/__support/OSUtil/linux/CMakeLists.txt
index 089cad454d534..95a83d77d0257 100644
--- a/libc/src/__support/OSUtil/linux/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/linux/CMakeLists.txt
@@ -23,3 +23,16 @@ add_object_library(
libc.hdr.types.struct_f_owner_ex
libc.hdr.types.off_t
)
+
+add_object_library(
+ pid
+ SRCS
+ pid.cpp
+ HDRS
+ ../pid.h
+ DEPENDS
+ libc.src.__support.OSUtil.osutil
+ libc.src.__support.common
+ libc.hdr.types.pid_t
+ libc.include.sys_syscall
+)
diff --git a/libc/src/__support/OSUtil/linux/pid.cpp b/libc/src/__support/OSUtil/linux/pid.cpp
new file mode 100644
index 0000000000000..a8499af596229
--- /dev/null
+++ b/libc/src/__support/OSUtil/linux/pid.cpp
@@ -0,0 +1,20 @@
+//===------------ pid_t utilities implementation ----------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/OSUtil/pid.h"
+#include "src/__support/OSUtil/syscall.h"
+#include <sys/syscall.h>
+
+namespace LIBC_NAMESPACE_DECL {
+
+pid_t ProcessIdentity::cache = -1;
+pid_t ProcessIdentity::get_uncached() {
+ return syscall_impl<pid_t>(SYS_getpid);
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/__support/OSUtil/pid.h b/libc/src/__support/OSUtil/pid.h
new file mode 100644
index 0000000000000..d723abe728569
--- /dev/null
+++ b/libc/src/__support/OSUtil/pid.h
@@ -0,0 +1,41 @@
+//===------------ pid_t utilities -------------------------------*- 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___SUPPORT_OSUTIL_PID_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_PID_H
+#include "hdr/types/pid_t.h"
+#include "src/__support/macros/attributes.h"
+#include "src/__support/macros/optimization.h"
+
+#ifndef LIBC_COPT_ENABLE_PID_CACHE
+#define LIBC_COPT_ENABLE_PID_CACHE 1
+#endif
+
+namespace LIBC_NAMESPACE_DECL {
+
+class ProcessIdentity {
+ static LIBC_INLINE_VAR thread_local bool fork_inflight = true;
+ static pid_t cache;
+ static pid_t get_uncached();
+
+public:
+ LIBC_INLINE static void start_fork() { fork_inflight = true; }
+ LIBC_INLINE static void end_fork() { fork_inflight = false; }
+ LIBC_INLINE static void refresh_cache() { cache = get_uncached(); }
+ LIBC_INLINE static pid_t get() {
+#if LIBC_COPT_ENABLE_PID_CACHE
+ if (LIBC_LIKELY(!fork_inflight))
+ return cache;
+#endif
+ return get_uncached();
+ }
+};
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_PID_H
diff --git a/libc/src/__support/threads/CMakeLists.txt b/libc/src/__support/threads/CMakeLists.txt
index d2e46b8e2574e..f1a2f162acfc2 100644
--- a/libc/src/__support/threads/CMakeLists.txt
+++ b/libc/src/__support/threads/CMakeLists.txt
@@ -44,6 +44,12 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.mutex)
)
endif()
+if (LIBC_CONF_ENABLE_TID_CACHE)
+ set(libc_copt_enable_tid_cache 1)
+else()
+ set(libc_copt_enable_tid_cache 0)
+endif()
+
add_header_library(
thread_common
HDRS
@@ -54,6 +60,9 @@ add_header_library(
libc.src.__support.CPP.optional
libc.src.__support.CPP.string_view
libc.src.__support.CPP.stringstream
+ libc.hdr.types.pid_t
+ COMPILE_OPTIONS
+ -DLIBC_COPT_ENABLE_TID_CACHE=${libc_copt_enable_tid_cache}
)
if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.thread)
@@ -89,3 +98,21 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.CndVar)
.${LIBC_TARGET_OS}.CndVar
)
endif()
+
+set(tid_dep)
+if (LLVM_LIBC_FULL_BUILD)
+ list(APPEND tid_dep libc.src.__support.thread)
+else()
+ list(APPEND tid_dep libc.src.__support.OSUtil.osutil)
+ list(APPEND tid_dep libc.include.sys_syscall)
+endif()
+
+add_header_library(
+ tid
+ HDRS
+ tid.h
+ DEPENDS
+ libc.src.__support.common
+ libc.hdr.types.pid_t
+ ${tid_dep}
+)
diff --git a/libc/src/__support/threads/linux/CMakeLists.txt b/libc/src/__support/threads/linux/CMakeLists.txt
index 8b7971584e77e..d86441dd67cd7 100644
--- a/libc/src/__support/threads/linux/CMakeLists.txt
+++ b/libc/src/__support/threads/linux/CMakeLists.txt
@@ -55,6 +55,7 @@ add_header_library(
libc.src.__support.common
libc.src.__support.OSUtil.osutil
libc.src.__support.CPP.limits
+ libc.src.__support.threads.tid
COMPILE_OPTIONS
-DLIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT=${LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT}
${monotonicity_flags}
diff --git a/libc/src/__support/threads/linux/rwlock.h b/libc/src/__support/threads/linux/rwlock.h
index d2fb0ce1a3c08..cae8aa6410686 100644
--- a/libc/src/__support/threads/linux/rwlock.h
+++ b/libc/src/__support/threads/linux/rwlock.h
@@ -23,6 +23,7 @@
#include "src/__support/threads/linux/futex_word.h"
#include "src/__support/threads/linux/raw_mutex.h"
#include "src/__support/threads/sleep.h"
+#include "src/__support/threads/tid.h"
#ifndef LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT
#define LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT 100
@@ -336,8 +337,6 @@ class RwLock {
LIBC_INLINE Role get_preference() const {
return static_cast<Role>(preference);
}
- // TODO: use cached thread id once implemented.
- LIBC_INLINE static pid_t gettid() { return syscall_impl<pid_t>(SYS_gettid); }
template <Role role> LIBC_INLINE LockResult try_lock(RwState &old) {
if constexpr (role == Role::Reader) {
@@ -359,7 +358,7 @@ class RwLock {
if (LIBC_LIKELY(old.compare_exchange_weak_with(
state, old.set_writer_bit(), cpp::MemoryOrder::ACQUIRE,
cpp::MemoryOrder::RELAXED))) {
- writer_tid.store(gettid(), cpp::MemoryOrder::RELAXED);
+ writer_tid.store(gettid_inline(), cpp::MemoryOrder::RELAXED);
return LockResult::Success;
}
// Notice that old is updated by the compare_exchange_weak_with
@@ -394,7 +393,7 @@ class RwLock {
unsigned spin_count = LIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT) {
// Phase 1: deadlock detection.
// A deadlock happens if this is a RAW/WAW lock in the same thread.
- if (writer_tid.load(cpp::MemoryOrder::RELAXED) == gettid())
+ if (writer_tid.load(cpp::MemoryOrder::RELAXED) == gettid_inline())
return LockResult::Deadlock;
#if LIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY
@@ -520,7 +519,7 @@ class RwLock {
if (old.has_active_writer()) {
// The lock is held by a writer.
// Check if we are the owner of the lock.
- if (writer_tid.load(cpp::MemoryOrder::RELAXED) != gettid())
+ if (writer_tid.load(cpp::MemoryOrder::RELAXED) != gettid_inline())
return LockResult::PermissionDenied;
// clear writer tid.
writer_tid.store(0, cpp::MemoryOrder::RELAXED);
diff --git a/libc/src/__support/threads/linux/thread.cpp b/libc/src/__support/threads/linux/thread.cpp
index 36b4a88eba9b4..c8ad086f3d1cb 100644
--- a/libc/src/__support/threads/linux/thread.cpp
+++ b/libc/src/__support/threads/linux/thread.cpp
@@ -518,4 +518,6 @@ void thread_exit(ThreadReturnValue retval, ThreadStyle style) {
__builtin_unreachable();
}
+pid_t Thread::get_uncached_tid() { return syscall_impl<pid_t>(SYS_gettid); }
+
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/__support/threads/thread.h b/libc/src/__support/threads/thread.h
index ce23a880e048a..1805b6fd6182a 100644
--- a/libc/src/__support/threads/thread.h
+++ b/libc/src/__support/threads/thread.h
@@ -9,6 +9,11 @@
#ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
#define LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
+#ifndef LIBC_COPT_ENABLE_TID_CACHE
+#define LIBC_COPT_ENABLE_TID_CACHE 1
+#endif
+
+#include "hdr/types/pid_t.h"
#include "src/__support/CPP/atomic.h"
#include "src/__support/CPP/optional.h"
#include "src/__support/CPP/string_view.h"
@@ -103,7 +108,7 @@ struct alignas(STACK_ALIGNMENT) ThreadAttributes {
uintptr_t tls; // Address to the thread TLS memory
uintptr_t tls_size; // The size of area pointed to by |tls|.
unsigned char owned_stack; // Indicates if the thread owns this stack memory
- int tid;
+ pid_t tid;
ThreadStyle style;
ThreadReturnValue retval;
ThreadAtExitCallbackMgr *atexit_callback_mgr;
@@ -228,6 +233,26 @@ struct Thread {
// Return the name of the thread in |name|. Return the error number of error.
int get_name(cpp::StringStream &name) const;
+
+ static pid_t get_uncached_tid();
+
+ LIBC_INLINE void refresh_tid(pid_t cached = -1) {
+ if (cached >= 0)
+ this->attrib->tid = cached;
+ else
+ this->attrib->tid = get_uncached_tid();
+ }
+ LIBC_INLINE void invalidate_tid() { this->attrib->tid = -1; }
+
+ LIBC_INLINE pid_t get_tid() {
+#if LIBC_COPT_ENABLE_TID_CACHE
+ if (LIBC_UNLIKELY(this->attrib->tid < 0))
+ return get_uncached_tid();
+ return this->attrib->tid;
+#else
+ return get_uncached_tid();
+#endif
+ }
};
extern LIBC_THREAD_LOCAL Thread self;
diff --git a/libc/src/__support/threads/tid.h b/libc/src/__support/threads/tid.h
new file mode 100644
index 0000000000000..a575cff508a0f
--- /dev/null
+++ b/libc/src/__support/threads/tid.h
@@ -0,0 +1,34 @@
+//===--- Tid wrapper --------------------------------------------*- 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___SUPPORT_THREADS_TID_H
+#define LLVM_LIBC_SRC___SUPPORT_THREADS_TID_H
+
+// This header is for internal usage which automatically dispatches full build
+// and overlay build behaviors.
+
+#include "hdr/types/pid_t.h"
+#include "src/__support/common.h"
+#ifdef LIBC_FULL_BUILD
+#include "src/__support/threads/thread.h"
+#else
+#include "src/__support/OSUtil/syscall.h"
+#include <sys/syscall.h>
+#endif // LIBC_FULL_BUILD
+
+namespace LIBC_NAMESPACE_DECL {
+LIBC_INLINE pid_t gettid_inline() {
+#ifdef LIBC_FULL_BUILD
+ return self.get_tid();
+#else
+ return syscall_impl<pid_t>(SYS_gettid);
+#endif
+}
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_THREADS_TID_H
diff --git a/libc/src/unistd/CMakeLists.txt b/libc/src/unistd/CMakeLists.txt
index ddafcd7c92f21..ec767128588f6 100644
--- a/libc/src/unistd/CMakeLists.txt
+++ b/libc/src/unistd/CMakeLists.txt
@@ -333,3 +333,13 @@ add_entrypoint_external(
add_entrypoint_external(
opterr
)
+
+add_entrypoint_object(
+ gettid
+ SRCS
+ gettid.cpp
+ HDRS
+ gettid.h
+ DEPENDS
+ libc.src.__support.threads.tid
+)
diff --git a/libc/src/unistd/getpid.h b/libc/src/unistd/getpid.h
index c3c55b0c06b10..5812df0dfecd6 100644
--- a/libc/src/unistd/getpid.h
+++ b/libc/src/unistd/getpid.h
@@ -9,12 +9,12 @@
#ifndef LLVM_LIBC_SRC_UNISTD_GETPID_H
#define LLVM_LIBC_SRC_UNISTD_GETPID_H
+#include "hdr/types/pid_t.h"
#include "src/__support/macros/config.h"
-#include <unistd.h>
namespace LIBC_NAMESPACE_DECL {
-pid_t getpid();
+pid_t getpid(void);
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/unistd/gettid.cpp b/libc/src/unistd/gettid.cpp
new file mode 100644
index 0000000000000..6d8ed65fb753d
--- /dev/null
+++ b/libc/src/unistd/gettid.cpp
@@ -0,0 +1,17 @@
+//===-- Implementation file for gettid --------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/unistd/gettid.h"
+#include "src/__support/common.h"
+#include "src/__support/threads/tid.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(pid_t, gettid, (void)) { return gettid_inline(); }
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/unistd/gettid.h b/libc/src/unistd/gettid.h
new file mode 100644
index 0000000000000..42283191be49b
--- /dev/null
+++ b/libc/src/unistd/gettid.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for gettid ------------------------*- 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_UNISTD_GETTID_H
+#define LLVM_LIBC_SRC_UNISTD_GETTID_H
+
+#include "hdr/types/pid_t.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+pid_t gettid(void);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_UNISTD_GETTID_H
diff --git a/libc/src/unistd/linux/CMakeLists.txt b/libc/src/unistd/linux/CMakeLists.txt
index 7e733d7f002c3..651ea60d07a30 100644
--- a/libc/src/unistd/linux/CMakeLists.txt
+++ b/libc/src/unistd/linux/CMakeLists.txt
@@ -101,6 +101,7 @@ add_entrypoint_object(
libc.inc...
[truncated]
``````````
</details>
https://github.com/llvm/llvm-project/pull/99765
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