Implement a new mechanism to let Scudo access the TLS slot
An upcoming change to Scudo will change how we use the TLS slot
in tsd_shared.h, which will be a little easier to deal with if
we can remove the code path that calls pthread_getspecific and
pthread_setspecific. The only known user of this code path is Fuchsia.
We can't eliminate this code path by making Fuchsia use ELF TLS
because although Fuchsia supports ELF TLS, it is not supported within
libc itself. To address this, Roland McGrath on the Fuchsia team has
proposed that Scudo will optionally call a platform-provided function
to access a TLS slot reserved for Scudo. Android also has a reserved
TLS slot, but the code that accesses the TLS slot lives in Scudo.
We can eliminate some complexity and duplicated code by having Android
implement the same mechanism that was proposed for Fuchsia, which is
what this change does. A separate change to Scudo will make use of it.
Bug: 163630045
Change-Id: I4678105c9c47a23feb5a5e80a314416de4556d9c
diff --git a/libc/platform/scudo_platform_tls_slot.h b/libc/platform/scudo_platform_tls_slot.h
new file mode 100644
index 0000000..9d017c0
--- /dev/null
+++ b/libc/platform/scudo_platform_tls_slot.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "bionic/tls.h"
+
+inline uintptr_t *getPlatformAllocatorTlsSlot() {
+ return reinterpret_cast<uintptr_t*>(&__get_tls()[TLS_SLOT_SANITIZER]);
+}
