Revert "[libc] implement cached process/thread identity" (#99559)

Reverts #98989

Author: SchrodingerZhu

libc/config/config.json

@@ -75,16 +75,6 @@
     "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": {

libc/config/linux/aarch64/entrypoints.txt

@@ -297,7 +297,6 @@ 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

libc/config/linux/riscv/entrypoints.txt

@@ -296,7 +296,6 @@ 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

libc/config/linux/x86_64/entrypoints.txt

@@ -315,7 +315,6 @@ 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

libc/docs/configure.rst

@@ -52,6 +52,3 @@ 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.

libc/docs/dev/undefined_behavior.rst

@@ -93,26 +93,3 @@ 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.

libc/spec/posix.td

@@ -546,11 +546,6 @@ def POSIX : StandardSpec<"POSIX"> {
           RetValSpec<PidT>,
           [ArgSpec<VoidType>]
         >,
-        FunctionSpec<
-          "gettid",
-          RetValSpec<PidT>,
-          [ArgSpec<VoidType>]
-        >,
         FunctionSpec<
           "getuid",
           RetValSpec<UidT>,
@@ -606,6 +601,16 @@ def POSIX : StandardSpec<"POSIX"> {
           RetValSpec<IntType>,
           [ArgSpec<ConstCharPtr>]
         >,
+        FunctionSpec<
+          "getpid",
+          RetValSpec<IntType>,
+          [ArgSpec<VoidType>]
+        >,
+        FunctionSpec<
+          "getppid",
+          RetValSpec<IntType>,
+          [ArgSpec<VoidType>]
+        >,
         FunctionSpec<
           "link",
           RetValSpec<IntType>,

libc/src/__support/OSUtil/CMakeLists.txt

@@ -15,20 +15,3 @@ 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()

libc/src/__support/OSUtil/linux/CMakeLists.txt

@@ -23,16 +23,3 @@ 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
-)