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34 #include "pthread_internal.h"
36 extern "C" pid_t __bionic_clone(uint32_t flags, void* child_stack, int* parent_tid, void* tls, int* child_tid, int (*fn)(void*), void* arg);
37 extern "C" __noreturn void __exit(int status);
39 // Called from the __bionic_clone assembler to call the thread function then exit.
40 extern "C" __LIBC_HIDDEN__ void __start_thread(int (*fn)(void*), void* arg) {
41 pthread_internal_t* self = __get_thread();
42 if (self && self->tid == -1) {
43 self->tid = syscall(__NR_gettid);
46 int status = (*fn)(arg);
50 int clone(int (*fn)(void*), void* child_stack, int flags, void* arg, ...) {
51 int* parent_tid = NULL;
53 int* child_tid = NULL;
55 if (fn != nullptr && child_stack == nullptr) {
60 // Extract any optional parameters required by the flags.
63 if ((flags & (CLONE_PARENT_SETTID|CLONE_SETTLS|CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
64 parent_tid = va_arg(args, int*);
66 if ((flags & (CLONE_SETTLS|CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
67 new_tls = va_arg(args, void*);
69 if ((flags & (CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID)) != 0) {
70 child_tid = va_arg(args, int*);
74 // Align 'child_stack' to 16 bytes.
75 uintptr_t child_stack_addr = reinterpret_cast<uintptr_t>(child_stack);
76 child_stack_addr &= ~0xf;
77 child_stack = reinterpret_cast<void*>(child_stack_addr);
79 // Remember the parent pid and invalidate the cached value while we clone.
80 pthread_internal_t* self = __get_thread();
81 pid_t parent_pid = self->invalidate_cached_pid();
83 // Remmber the caller's tid so that it can be restored in the parent after clone.
84 pid_t caller_tid = self->tid;
85 // Invalidate the tid before the syscall. The value is lazily cached in gettid(),
86 // and it will be updated by fork() and pthread_create(). We don't do this if
87 // we are sharing address space with the child.
88 if (!(flags & (CLONE_VM|CLONE_VFORK))) {
92 // Actually do the clone.
95 clone_result = __bionic_clone(flags, child_stack, parent_tid, new_tls, child_tid, fn, arg);
97 #if defined(__x86_64__) // sys_clone's last two arguments are flipped on x86-64.
98 clone_result = syscall(__NR_clone, flags, child_stack, parent_tid, child_tid, new_tls);
100 clone_result = syscall(__NR_clone, flags, child_stack, parent_tid, new_tls, child_tid);
104 if (clone_result != 0) {
105 // We're the parent, so put our known pid and tid back in place.
106 // We leave the child without a cached pid and tid, but:
107 // 1. pthread_create gives its children their own pthread_internal_t with the correct pid and tid.
108 // 2. fork uses CLONE_CHILD_SETTID to get the new pid/tid.
109 // 3. The tid is lazily fetched in gettid().
110 // If any other cases become important, we could use a double trampoline like __pthread_start.
111 self->set_cached_pid(parent_pid);
112 self->tid = caller_tid;
113 } else if (self->tid == -1) {
114 self->tid = syscall(__NR_gettid);
115 self->set_cached_pid(self->tid);