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/linker/linker_tls.cpp b/linker/linker_tls.cpp
index 0d1796b..a3aa9bf 100644
--- a/linker/linker_tls.cpp
+++ b/linker/linker_tls.cpp
@@ -31,6 +31,7 @@
#include <vector>
#include "private/ScopedRWLock.h"
+#include "private/ScopedSignalBlocker.h"
#include "private/bionic_defs.h"
#include "private/bionic_elf_tls.h"
#include "private/bionic_globals.h"
@@ -41,9 +42,6 @@
static bool g_static_tls_finished;
static std::vector<TlsModule> g_tls_modules;
-static inline size_t module_id_to_idx(size_t id) { return id - 1; }
-static inline size_t module_idx_to_id(size_t idx) { return idx + 1; }
-
static size_t get_unused_module_index() {
for (size_t i = 0; i < g_tls_modules.size(); ++i) {
if (g_tls_modules[i].soinfo_ptr == nullptr) {
@@ -57,37 +55,47 @@
}
static void register_tls_module(soinfo* si, size_t static_offset) {
+ TlsModules& libc_modules = __libc_shared_globals()->tls_modules;
+
// The global TLS module table points at the std::vector of modules declared
// in this file, so acquire a write lock before modifying the std::vector.
- ScopedWriteLock locker(&__libc_shared_globals()->tls_modules.rwlock);
+ ScopedSignalBlocker ssb;
+ ScopedWriteLock locker(&libc_modules.rwlock);
size_t module_idx = get_unused_module_index();
soinfo_tls* si_tls = si->get_tls();
- si_tls->module_id = module_idx_to_id(module_idx);
+ si_tls->module_id = __tls_module_idx_to_id(module_idx);
+
+ const size_t new_generation = ++libc_modules.generation;
+ __libc_tls_generation_copy = new_generation;
+ if (libc_modules.generation_libc_so != nullptr) {
+ *libc_modules.generation_libc_so = new_generation;
+ }
g_tls_modules[module_idx] = {
.segment = si_tls->segment,
.static_offset = static_offset,
- .first_generation = ++__libc_shared_globals()->tls_modules.generation,
+ .first_generation = new_generation,
.soinfo_ptr = si,
};
}
static void unregister_tls_module(soinfo* si) {
+ ScopedSignalBlocker ssb;
ScopedWriteLock locker(&__libc_shared_globals()->tls_modules.rwlock);
soinfo_tls* si_tls = si->get_tls();
- TlsModule& mod = g_tls_modules[module_id_to_idx(si_tls->module_id)];
+ TlsModule& mod = g_tls_modules[__tls_module_id_to_idx(si_tls->module_id)];
CHECK(mod.static_offset == SIZE_MAX);
CHECK(mod.soinfo_ptr == si);
mod = {};
- si_tls->module_id = kUninitializedModuleId;
+ si_tls->module_id = kTlsUninitializedModuleId;
}
// The reference is valid until a TLS module is registered or unregistered.
const TlsModule& get_tls_module(size_t module_id) {
- size_t module_idx = module_id_to_idx(module_id);
+ size_t module_idx = __tls_module_id_to_idx(module_id);
CHECK(module_idx < g_tls_modules.size());
return g_tls_modules[module_idx];
}
@@ -123,7 +131,7 @@
void register_soinfo_tls(soinfo* si) {
soinfo_tls* si_tls = si->get_tls();
- if (si_tls == nullptr || si_tls->module_id != kUninitializedModuleId) {
+ if (si_tls == nullptr || si_tls->module_id != kTlsUninitializedModuleId) {
return;
}
size_t static_offset = SIZE_MAX;
@@ -136,7 +144,7 @@
void unregister_soinfo_tls(soinfo* si) {
soinfo_tls* si_tls = si->get_tls();
- if (si_tls == nullptr || si_tls->module_id == kUninitializedModuleId) {
+ if (si_tls == nullptr || si_tls->module_id == kTlsUninitializedModuleId) {
return;
}
return unregister_tls_module(si);