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

1 files changed, 2 insertions, 0 deletions

diff --git a/libc/private/bionic_globals.h b/libc/private/bionic_globals.h
index 4d40476a5..21a2a249b 100644
--- a/libc/private/bionic_globals.h
+++ b/libc/private/bionic_globals.h
@@ -33,6 +33,7 @@
 #include <link.h>
 #include <pthread.h>
 
+#include "private/bionic_allocator.h"
 #include "private/bionic_elf_tls.h"
 #include "private/bionic_fdsan.h"
 #include "private/bionic_malloc_dispatch.h"
@@ -70,6 +71,7 @@ struct libc_shared_globals {
 
   StaticTlsLayout static_tls_layout;
   TlsModules tls_modules;
+  BionicAllocator tls_allocator;
 
   // Values passed from the linker to libc.so.
   const char* init_progname = nullptr;