[libc-commits] [libc] [libc] implement cached process/thread identity (PR #95965)
Schrodinger ZHU Yifan via libc-commits
libc-commits at lists.llvm.org
Wed Jun 19 12:33:20 PDT 2024
https://github.com/SchrodingerZhu updated https://github.com/llvm/llvm-project/pull/95965
>From 81d97d32a743164a5a27580f60d13c5847d1b1b0 Mon Sep 17 00:00:00 2001
From: Yifan Zhu <yifzhu at nvidia.com>
Date: Tue, 18 Jun 2024 11:13:09 -0700
Subject: [PATCH 1/4] [libc] implement cached process/thread identity
---
libc/config/linux/aarch64/entrypoints.txt | 1 +
libc/config/linux/riscv/entrypoints.txt | 1 +
libc/config/linux/x86_64/entrypoints.txt | 1 +
libc/docs/dev/undefined_behavior.rst | 21 ++++++++++++
libc/spec/posix.td | 15 +++-----
libc/src/__support/OSUtil/CMakeLists.txt | 9 +++++
.../src/__support/OSUtil/linux/CMakeLists.txt | 13 +++++++
libc/src/__support/OSUtil/linux/pid.cpp | 20 +++++++++++
libc/src/__support/OSUtil/pid.h | 32 +++++++++++++++++
libc/src/__support/threads/CMakeLists.txt | 19 +++++++++++
.../__support/threads/linux/CMakeLists.txt | 1 +
libc/src/__support/threads/linux/rwlock.h | 9 +++--
libc/src/__support/threads/linux/thread.cpp | 2 ++
libc/src/__support/threads/thread.h | 13 ++++++-
libc/src/__support/threads/tid.h | 34 +++++++++++++++++++
libc/src/unistd/CMakeLists.txt | 10 ++++++
libc/src/unistd/getpid.h | 4 +--
libc/src/unistd/gettid.cpp | 17 ++++++++++
libc/src/unistd/gettid.h | 21 ++++++++++++
libc/src/unistd/linux/CMakeLists.txt | 4 +--
libc/src/unistd/linux/fork.cpp | 28 +++++++++------
libc/src/unistd/linux/getpid.cpp | 10 ++----
libc/test/src/unistd/CMakeLists.txt | 10 ++++++
libc/test/src/unistd/gettid_test.cpp | 15 ++++++++
24 files changed, 272 insertions(+), 38 deletions(-)
create mode 100644 libc/src/__support/OSUtil/linux/pid.cpp
create mode 100644 libc/src/__support/OSUtil/pid.h
create mode 100644 libc/src/__support/threads/tid.h
create mode 100644 libc/src/unistd/gettid.cpp
create mode 100644 libc/src/unistd/gettid.h
create mode 100644 libc/test/src/unistd/gettid_test.cpp
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index dfed6acbdf257..a2643bda8277f 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -290,6 +290,7 @@ 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 e12d6b3957e51..ae0c64045da88 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -295,6 +295,7 @@ 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 cfe35167ca32e..0380d4a3734e8 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -308,6 +308,7 @@ 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/dev/undefined_behavior.rst b/libc/docs/dev/undefined_behavior.rst
index c97a539ca8da4..9f31aeff9ab97 100644
--- a/libc/docs/dev/undefined_behavior.rst
+++ b/libc/docs/dev/undefined_behavior.rst
@@ -89,3 +89,24 @@ The C23 standard states that if the value of the ``rnd`` argument of the
the value of a math rounding direction macro, the direction of rounding is
unspecified. LLVM's libc chooses to use the ``FP_INT_TONEAREST`` rounding
direction in this case.
+
+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.
+
+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 d14047548e104..c3996a213f60b 100644
--- a/libc/spec/posix.td
+++ b/libc/spec/posix.td
@@ -512,6 +512,11 @@ def POSIX : StandardSpec<"POSIX"> {
RetValSpec<PidT>,
[ArgSpec<VoidType>]
>,
+ FunctionSpec<
+ "gettid",
+ RetValSpec<PidT>,
+ [ArgSpec<VoidType>]
+ >,
FunctionSpec<
"getuid",
RetValSpec<UidT>,
@@ -567,16 +572,6 @@ 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..2db72f40c6f18 100644
--- a/libc/src/__support/OSUtil/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/CMakeLists.txt
@@ -15,3 +15,12 @@ add_object_library(
DEPENDS
${target_os_util}
)
+
+if(TARGET libc.src.__support.OSUtil.${LIBC_TARGET_OS}.pid)
+ add_object_library(
+ pid
+ ALIAS
+ DEPENDS
+ .${LIBC_TARGET_OS}.pid
+ )
+endif()
diff --git a/libc/src/__support/OSUtil/linux/CMakeLists.txt b/libc/src/__support/OSUtil/linux/CMakeLists.txt
index 78b117fd19439..ddc51aadd0d02 100644
--- a/libc/src/__support/OSUtil/linux/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/linux/CMakeLists.txt
@@ -22,3 +22,16 @@ add_object_library(
libc.hdr.types.struct_flock64
libc.hdr.types.struct_f_owner_ex
)
+
+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..47ef00565cbe9
--- /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 {
+
+pid_t ProcessIdentity::cache = -1;
+pid_t ProcessIdentity::get_uncached() {
+ return syscall_impl<pid_t>(SYS_getpid);
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/__support/OSUtil/pid.h b/libc/src/__support/OSUtil/pid.h
new file mode 100644
index 0000000000000..5fda6726308e1
--- /dev/null
+++ b/libc/src/__support/OSUtil/pid.h
@@ -0,0 +1,32 @@
+//===------------ 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"
+namespace LIBC_NAMESPACE {
+
+class ProcessIdentity {
+ static pid_t cache;
+ static pid_t get_uncached();
+
+public:
+ LIBC_INLINE static void invalidate_cache() { cache = -1; }
+ LIBC_INLINE static void refresh_cache() { cache = get_uncached(); }
+ LIBC_INLINE static pid_t get() {
+ if (LIBC_UNLIKELY(cache < 0))
+ return get_uncached();
+ return cache;
+ }
+};
+
+} // namespace LIBC_NAMESPACE
+
+#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 9ea0b59befe7a..ef8769ff9498e 100644
--- a/libc/src/__support/threads/CMakeLists.txt
+++ b/libc/src/__support/threads/CMakeLists.txt
@@ -45,6 +45,7 @@ add_header_library(
libc.src.__support.CPP.optional
libc.src.__support.CPP.string_view
libc.src.__support.CPP.stringstream
+ libc.hdr.types.pid_t
)
if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.thread)
@@ -80,3 +81,21 @@ 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
+ ${tid_dep}
+)
diff --git a/libc/src/__support/threads/linux/CMakeLists.txt b/libc/src/__support/threads/linux/CMakeLists.txt
index 95e509b7a825d..832617afb6068 100644
--- a/libc/src/__support/threads/linux/CMakeLists.txt
+++ b/libc/src/__support/threads/linux/CMakeLists.txt
@@ -55,6 +55,7 @@ add_header_library(
libc.src.__support.common
libc.src.__support.OSUtil.osutil
libc.src.__support.CPP.limits
+ libc.src.__support.threads.tid
COMPILE_OPTIONS
-DLIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT=${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 201fe92c37fc0..1faeeec1bb025 100644
--- a/libc/src/__support/threads/linux/rwlock.h
+++ b/libc/src/__support/threads/linux/rwlock.h
@@ -22,6 +22,7 @@
#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
@@ -335,8 +336,6 @@ 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) {
@@ -358,7 +357,7 @@ 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
@@ -393,7 +392,7 @@ 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
@@ -519,7 +518,7 @@ 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 1d986ff38cfff..493f2df7f8301 100644
--- a/libc/src/__support/threads/linux/thread.cpp
+++ b/libc/src/__support/threads/linux/thread.cpp
@@ -517,4 +517,6 @@ 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
diff --git a/libc/src/__support/threads/thread.h b/libc/src/__support/threads/thread.h
index acfe33879f878..e53ff9995f678 100644
--- a/libc/src/__support/threads/thread.h
+++ b/libc/src/__support/threads/thread.h
@@ -9,6 +9,7 @@
#ifndef LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
#define LLVM_LIBC_SRC___SUPPORT_THREADS_THREAD_H
+#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"
@@ -99,7 +100,7 @@ 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;
@@ -224,6 +225,16 @@ 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() { this->attrib->tid = get_uncached_tid(); }
+ LIBC_INLINE void invalidate_tid() { this->attrib->tid = -1; }
+ LIBC_INLINE pid_t get_tid() {
+ if (LIBC_UNLIKELY(this->attrib->tid < 0))
+ return get_uncached_tid();
+ return this->attrib->tid;
+ }
};
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..622f91543af7e
--- /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 {
+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
+
+#endif // LLVM_LIBC_SRC___SUPPORT_THREADS_TID_H
diff --git a/libc/src/unistd/CMakeLists.txt b/libc/src/unistd/CMakeLists.txt
index 77db76518350c..959595478bb7f 100644
--- a/libc/src/unistd/CMakeLists.txt
+++ b/libc/src/unistd/CMakeLists.txt
@@ -318,3 +318,13 @@ 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 5890dbf63681a..d7f589da81913 100644
--- a/libc/src/unistd/getpid.h
+++ b/libc/src/unistd/getpid.h
@@ -9,11 +9,11 @@
#ifndef LLVM_LIBC_SRC_UNISTD_GETPID_H
#define LLVM_LIBC_SRC_UNISTD_GETPID_H
-#include <unistd.h>
+#include "hdr/types/pid_t.h"
namespace LIBC_NAMESPACE {
-pid_t getpid();
+pid_t getpid(void);
} // namespace LIBC_NAMESPACE
diff --git a/libc/src/unistd/gettid.cpp b/libc/src/unistd/gettid.cpp
new file mode 100644
index 0000000000000..040a1323dcad1
--- /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 {
+
+LLVM_LIBC_FUNCTION(pid_t, gettid, (void)) { return gettid_inline(); }
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/unistd/gettid.h b/libc/src/unistd/gettid.h
new file mode 100644
index 0000000000000..01691b74895f7
--- /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 {
+
+pid_t gettid(void);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_UNISTD_GETTID_H
diff --git a/libc/src/unistd/linux/CMakeLists.txt b/libc/src/unistd/linux/CMakeLists.txt
index 7d831f9c29c74..4648870c708de 100644
--- a/libc/src/unistd/linux/CMakeLists.txt
+++ b/libc/src/unistd/linux/CMakeLists.txt
@@ -101,6 +101,7 @@ add_entrypoint_object(
libc.include.sys_syscall
libc.src.__support.threads.fork_callbacks
libc.src.__support.OSUtil.osutil
+ libc.src.__support.OSUtil.pid
libc.src.__support.threads.thread
libc.src.errno.errno
)
@@ -190,8 +191,7 @@ add_entrypoint_object(
../getpid.h
DEPENDS
libc.include.unistd
- libc.include.sys_syscall
- libc.src.__support.OSUtil.osutil
+ libc.src.__support.OSUtil.pid
)
add_entrypoint_object(
diff --git a/libc/src/unistd/linux/fork.cpp b/libc/src/unistd/linux/fork.cpp
index 6fa2b990b19a9..98721e2f5e1d8 100644
--- a/libc/src/unistd/linux/fork.cpp
+++ b/libc/src/unistd/linux/fork.cpp
@@ -8,12 +8,13 @@
#include "src/unistd/fork.h"
+#include "src/__support/OSUtil/pid.h"
#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
#include "src/__support/common.h"
#include "src/__support/threads/fork_callbacks.h"
#include "src/__support/threads/thread.h" // For thread self object
-
#include "src/errno/libc_errno.h"
+
#include <signal.h> // For SIGCHLD
#include <sys/syscall.h> // For syscall numbers.
@@ -24,6 +25,13 @@ namespace LIBC_NAMESPACE {
LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
invoke_prepare_callbacks();
+
+ // Invalidate tid/pid cache before fork to avoid post fork signal handler from
+ // getting wrong values. gettid() is not async-signal-safe, but let's provide
+ // our best efforts here.
+ self.invalidate_tid();
+ ProcessIdentity::invalidate_cache();
+
#ifdef SYS_fork
pid_t ret = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_fork);
#elif defined(SYS_clone)
@@ -31,15 +39,6 @@ LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
#else
#error "fork and clone syscalls not available."
#endif
- if (ret == 0) {
- // Return value is 0 in the child process.
- // The child is created with a single thread whose self object will be a
- // copy of parent process' thread which called fork. So, we have to fix up
- // the child process' self object with the new process' tid.
- self.attrib->tid = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_gettid);
- invoke_child_callbacks();
- return 0;
- }
if (ret < 0) {
// Error case, a child process was not created.
@@ -47,6 +46,15 @@ LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
return -1;
}
+ // Refresh tid/pid cache after fork
+ self.refresh_tid();
+ ProcessIdentity::refresh_cache();
+
+ if (ret == 0) {
+ invoke_child_callbacks();
+ return 0;
+ }
+
invoke_parent_callbacks();
return ret;
}
diff --git a/libc/src/unistd/linux/getpid.cpp b/libc/src/unistd/linux/getpid.cpp
index 85730738ca2ef..7446f2208d596 100644
--- a/libc/src/unistd/linux/getpid.cpp
+++ b/libc/src/unistd/linux/getpid.cpp
@@ -7,16 +7,10 @@
//===----------------------------------------------------------------------===//
#include "src/unistd/getpid.h"
-
-#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/OSUtil/pid.h"
#include "src/__support/common.h"
-
-#include <sys/syscall.h> // For syscall numbers.
-
namespace LIBC_NAMESPACE {
-LLVM_LIBC_FUNCTION(pid_t, getpid, ()) {
- return LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_getpid);
-}
+LLVM_LIBC_FUNCTION(pid_t, getpid, (void)) { return ProcessIdentity::get(); }
} // namespace LIBC_NAMESPACE
diff --git a/libc/test/src/unistd/CMakeLists.txt b/libc/test/src/unistd/CMakeLists.txt
index de3e8d9ccbb62..a526fa992eec1 100644
--- a/libc/test/src/unistd/CMakeLists.txt
+++ b/libc/test/src/unistd/CMakeLists.txt
@@ -376,6 +376,16 @@ add_libc_unittest(
libc.src.unistd.getpid
)
+add_libc_unittest(
+ gettid_test
+ SUITE
+ libc_unistd_unittests
+ SRCS
+ gettid_test.cpp
+ DEPENDS
+ libc.src.unistd.gettid
+)
+
add_libc_unittest(
getppid_test
SUITE
diff --git a/libc/test/src/unistd/gettid_test.cpp b/libc/test/src/unistd/gettid_test.cpp
new file mode 100644
index 0000000000000..c2330f4002279
--- /dev/null
+++ b/libc/test/src/unistd/gettid_test.cpp
@@ -0,0 +1,15 @@
+//===-- Unittests for gettid ----------------------------------------------===//
+//
+// 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 "test/UnitTest/Test.h"
+
+TEST(LlvmLibcGetTidTest, SmokeTest) {
+ // gettid always succeeds. So, we just call it as a smoke test.
+ ASSERT_GT(LIBC_NAMESPACE::gettid(), 0);
+}
>From 084ad55f547b52b58debad971580842bf8979232 Mon Sep 17 00:00:00 2001
From: Yifan Zhu <yifzhu at nvidia.com>
Date: Tue, 18 Jun 2024 11:31:55 -0700
Subject: [PATCH 2/4] initialize pid cache in startup
---
libc/startup/linux/CMakeLists.txt | 1 +
libc/startup/linux/do_start.cpp | 2 ++
2 files changed, 3 insertions(+)
diff --git a/libc/startup/linux/CMakeLists.txt b/libc/startup/linux/CMakeLists.txt
index 68f68ff45aa9e..f42fa3baeb290 100644
--- a/libc/startup/linux/CMakeLists.txt
+++ b/libc/startup/linux/CMakeLists.txt
@@ -96,6 +96,7 @@ add_object_library(
libc.include.sys_syscall
libc.src.__support.threads.thread
libc.src.__support.OSUtil.osutil
+ libc.src.__support.OSUtil.pid
libc.src.stdlib.exit
libc.src.stdlib.atexit
libc.src.unistd.environ
diff --git a/libc/startup/linux/do_start.cpp b/libc/startup/linux/do_start.cpp
index 55fd575f7ad0b..bc24a054726c3 100644
--- a/libc/startup/linux/do_start.cpp
+++ b/libc/startup/linux/do_start.cpp
@@ -6,6 +6,7 @@
//
//===----------------------------------------------------------------------===//
#include "startup/linux/do_start.h"
+#include "src/__support/OSUtil/pid.h"
#include "src/__support/OSUtil/syscall.h"
#include "src/__support/threads/thread.h"
#include "src/stdlib/atexit.h"
@@ -63,6 +64,7 @@ static ThreadAttributes main_thread_attrib;
auto tid = syscall_impl<long>(SYS_gettid);
if (tid <= 0)
syscall_impl<long>(SYS_exit, 1);
+ ProcessIdentity::refresh_cache();
main_thread_attrib.tid = static_cast<int>(tid);
// After the argv array, is a 8-byte long NULL value before the array of env
>From 0edf09f3bd9b2ce71c22a1ad7d3e95eee3e9249b Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <i at zhuyi.fan>
Date: Wed, 19 Jun 2024 12:04:21 -0700
Subject: [PATCH 3/4] add TLS-based fork-inflight guard
---
libc/src/__support/OSUtil/linux/pid.cpp | 1 +
libc/src/__support/OSUtil/pid.h | 6 ++++--
libc/src/unistd/linux/fork.cpp | 9 +++++++--
3 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/libc/src/__support/OSUtil/linux/pid.cpp b/libc/src/__support/OSUtil/linux/pid.cpp
index 47ef00565cbe9..632e250e40f0a 100644
--- a/libc/src/__support/OSUtil/linux/pid.cpp
+++ b/libc/src/__support/OSUtil/linux/pid.cpp
@@ -13,6 +13,7 @@
namespace LIBC_NAMESPACE {
pid_t ProcessIdentity::cache = -1;
+thread_local bool ProcessIdentity::fork_inflight = false;
pid_t ProcessIdentity::get_uncached() {
return syscall_impl<pid_t>(SYS_getpid);
}
diff --git a/libc/src/__support/OSUtil/pid.h b/libc/src/__support/OSUtil/pid.h
index 5fda6726308e1..6349f06125d30 100644
--- a/libc/src/__support/OSUtil/pid.h
+++ b/libc/src/__support/OSUtil/pid.h
@@ -14,14 +14,16 @@
namespace LIBC_NAMESPACE {
class ProcessIdentity {
+ static thread_local bool fork_inflight;
static pid_t cache;
static pid_t get_uncached();
public:
- LIBC_INLINE static void invalidate_cache() { cache = -1; }
+ 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_UNLIKELY(cache < 0))
+ if (LIBC_UNLIKELY(fork_inflight))
return get_uncached();
return cache;
}
diff --git a/libc/src/unistd/linux/fork.cpp b/libc/src/unistd/linux/fork.cpp
index 98721e2f5e1d8..f7fb5a9a42cd9 100644
--- a/libc/src/unistd/linux/fork.cpp
+++ b/libc/src/unistd/linux/fork.cpp
@@ -30,7 +30,7 @@ LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
// getting wrong values. gettid() is not async-signal-safe, but let's provide
// our best efforts here.
self.invalidate_tid();
- ProcessIdentity::invalidate_cache();
+ ProcessIdentity::start_fork();
#ifdef SYS_fork
pid_t ret = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_fork);
@@ -46,15 +46,20 @@ LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
return -1;
}
+ // Common
// Refresh tid/pid cache after fork
self.refresh_tid();
- ProcessIdentity::refresh_cache();
+ // Child process
if (ret == 0) {
+ ProcessIdentity::refresh_cache();
+ ProcessIdentity::end_fork();
invoke_child_callbacks();
return 0;
}
+ // Parent process
+ ProcessIdentity::end_fork();
invoke_parent_callbacks();
return ret;
}
>From 030fe3acc7715ca2097d750b35b08a9d9b628dfb Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <i at zhuyi.fan>
Date: Wed, 19 Jun 2024 12:33:03 -0700
Subject: [PATCH 4/4] add options and docs
---
libc/config/config.json | 12 +++++++++++-
libc/docs/configure.rst | 3 +++
libc/docs/dev/undefined_behavior.rst | 4 +++-
libc/src/__support/OSUtil/CMakeLists.txt | 8 ++++++++
libc/src/__support/OSUtil/pid.h | 9 +++++++++
libc/src/__support/threads/CMakeLists.txt | 8 ++++++++
libc/src/__support/threads/thread.h | 9 +++++++++
7 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/libc/config/config.json b/libc/config/config.json
index 8d6a84e732597..c7b570ac719d0 100644
--- a/libc/config/config.json
+++ b/libc/config/config.json
@@ -54,5 +54,15 @@
"value": 100,
"doc": "Default number of spins before blocking if a rwlock is in contention (default to 100)."
}
+ },
+ "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."
+ }
}
-}
+}
\ No newline at end of file
diff --git a/libc/docs/configure.rst b/libc/docs/configure.rst
index bdae6c54052f2..ef74161aae92e 100644
--- a/libc/docs/configure.rst
+++ b/libc/docs/configure.rst
@@ -41,3 +41,6 @@ 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 fulldefault 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 9f31aeff9ab97..9894441be0307 100644
--- a/libc/docs/dev/undefined_behavior.rst
+++ b/libc/docs/dev/undefined_behavior.rst
@@ -95,7 +95,9 @@ 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 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``
------------------------------------------
diff --git a/libc/src/__support/OSUtil/CMakeLists.txt b/libc/src/__support/OSUtil/CMakeLists.txt
index 2db72f40c6f18..517f888178718 100644
--- a/libc/src/__support/OSUtil/CMakeLists.txt
+++ b/libc/src/__support/OSUtil/CMakeLists.txt
@@ -16,11 +16,19 @@ add_object_library(
${target_os_util}
)
+if (LIBC_CONF_ENABLE_PID_CACHE)
+ set(libc_copt_enable_pid_cache 1)
+else()
+ set(libc_copt_enable_pid_cache 0)
+endif()
+
if(TARGET libc.src.__support.OSUtil.${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/pid.h b/libc/src/__support/OSUtil/pid.h
index 6349f06125d30..4183c82df3655 100644
--- a/libc/src/__support/OSUtil/pid.h
+++ b/libc/src/__support/OSUtil/pid.h
@@ -11,6 +11,11 @@
#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 {
class ProcessIdentity {
@@ -23,9 +28,13 @@ class ProcessIdentity {
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_UNLIKELY(fork_inflight))
return get_uncached();
return cache;
+#else
+ return get_uncached();
+#endif
}
};
diff --git a/libc/src/__support/threads/CMakeLists.txt b/libc/src/__support/threads/CMakeLists.txt
index ef8769ff9498e..55ea474388072 100644
--- a/libc/src/__support/threads/CMakeLists.txt
+++ b/libc/src/__support/threads/CMakeLists.txt
@@ -35,6 +35,12 @@ if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.mutex)
)
endif()
+if (LIBC_CONF_ENABLE_TID_CACHE)
+ set(libc_copt_enable_tid_cache 1)
+else()
+ set(libc_copt_enable_tid_cache 0)
+endif()
+
add_header_library(
thread_common
HDRS
@@ -46,6 +52,8 @@ add_header_library(
libc.src.__support.CPP.string_view
libc.src.__support.CPP.stringstream
libc.hdr.types.pid_t
+ COMPILE_OPTIONS
+ -DLIBC_COPT_ENABLE_TID_CACHE=${libc_copt_enable_tid_cache}
)
if(TARGET libc.src.__support.threads.${LIBC_TARGET_OS}.thread)
diff --git a/libc/src/__support/threads/thread.h b/libc/src/__support/threads/thread.h
index e53ff9995f678..5f4d9a2224c36 100644
--- a/libc/src/__support/threads/thread.h
+++ b/libc/src/__support/threads/thread.h
@@ -9,6 +9,10 @@
#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"
@@ -230,10 +234,15 @@ struct Thread {
LIBC_INLINE void refresh_tid() { 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
}
};
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