Implement dynamic TLS accesses and allocation
Initialize a thread's DTV to an empty zeroed DTV. Allocate the DTV and
any ELF module's TLS segment on-demand in __tls_get_addr. Use a generation
counter, incremented in the linker, to signal when threads should
update/reallocate their DTV objects.
A generation count of 0 always indicates the constant zero DTV.
Once a DTV is allocated, it isn't freed until the thread exits, because
a signal handler could interrupt the fast path of __tls_get_addr between
accessing the DTV slot and reading a field of the DTV. Bionic keeps a
linked list of DTV objects so it can free them at thread-exit.
Dynamic TLS memory is allocated using a BionicAllocator instance in
libc_shared_globals. For async-signal safety, access to the
linker/libc-shared state is protected by first blocking signals, then by
acquiring the reader-writer lock, TlsModules::rwlock. A write lock is
needed to allocate or free memory.
In pthread_exit, unconditionally block signals before freeing dynamic
TLS memory or freeing the shadow call stack.
ndk_cruft.cpp: Avoid including pthread_internal.h inside an extern "C".
(The header now includes a C++ template that doesn't compile inside
extern "C".)
Bug: http://b/78026329
Bug: http://b/123094171
Test: bionic unit tests
Change-Id: I3c9b12921c9e68b33dcc1d1dd276bff364eff5d7
diff --git a/libc/bionic/pthread_exit.cpp b/libc/bionic/pthread_exit.cpp
index 84ea2e6..3b873b3 100644
--- a/libc/bionic/pthread_exit.cpp
+++ b/libc/bionic/pthread_exit.cpp
@@ -98,15 +98,22 @@
thread->alternate_signal_stack = nullptr;
}
+ ThreadJoinState old_state = THREAD_NOT_JOINED;
+ while (old_state == THREAD_NOT_JOINED &&
+ !atomic_compare_exchange_weak(&thread->join_state, &old_state, THREAD_EXITED_NOT_JOINED)) {
+ }
+
+ // We don't want to take a signal after unmapping the stack, the shadow call
+ // stack, or dynamic TLS memory.
+ ScopedSignalBlocker ssb;
+
#ifdef __aarch64__
// Free the shadow call stack and guard pages.
munmap(thread->shadow_call_stack_guard_region, SCS_GUARD_REGION_SIZE);
#endif
- ThreadJoinState old_state = THREAD_NOT_JOINED;
- while (old_state == THREAD_NOT_JOINED &&
- !atomic_compare_exchange_weak(&thread->join_state, &old_state, THREAD_EXITED_NOT_JOINED)) {
- }
+ // Free the ELF TLS DTV and all dynamically-allocated ELF TLS memory.
+ __free_dynamic_tls(__get_bionic_tcb());
if (old_state == THREAD_DETACHED) {
// The thread is detached, no one will use pthread_internal_t after pthread_exit.
@@ -121,10 +128,6 @@
if (thread->mmap_size != 0) {
// We need to free mapped space for detached threads when they exit.
// That's not something we can do in C.
-
- // We don't want to take a signal after we've unmapped the stack.
- // That's one last thing we can do before dropping to assembler.
- ScopedSignalBlocker ssb;
__hwasan_thread_exit();
_exit_with_stack_teardown(thread->mmap_base, thread->mmap_size);
}