Defend against -fstack-protector in libc startup.
Exactly which functions get a stack protector is up to the compiler, so
let's separate the code that sets up the environment stack protection
requires and explicitly build it with -fno-stack-protector.
Bug: http://b/26276517
Change-Id: I8719e23ead1f1e81715c32c1335da868f68369b5
diff --git a/libc/bionic/__libc_init_main_thread.cpp b/libc/bionic/__libc_init_main_thread.cpp
new file mode 100644
index 0000000..e1445cb
--- /dev/null
+++ b/libc/bionic/__libc_init_main_thread.cpp
@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) 2008 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.
+ */
+
+#include "libc_init_common.h"
+
+#include "private/bionic_auxv.h"
+#include "private/bionic_globals.h"
+#include "private/KernelArgumentBlock.h"
+#include "pthread_internal.h"
+
+extern "C" int __set_tls(void* ptr);
+extern "C" int __set_tid_address(int* tid_address);
+
+// Setup for the main thread. For dynamic executables, this is called by the
+// linker _before_ libc is mapped in memory. This means that all writes to
+// globals from this function will apply to linker-private copies and will not
+// be visible from libc later on.
+//
+// Note: this function creates a pthread_internal_t for the initial thread and
+// stores the pointer in TLS, but does not add it to pthread's thread list. This
+// has to be done later from libc itself (see __libc_init_common).
+//
+// This is in a file by itself because it needs to be built with
+// -fno-stack-protector because it's responsible for setting up the main
+// thread's TLS (which stack protector relies on).
+
+void __libc_init_main_thread(KernelArgumentBlock& args) {
+ __libc_auxv = args.auxv;
+
+ static pthread_internal_t main_thread;
+
+ // The -fstack-protector implementation uses TLS, so make sure that's
+ // set up before we call any function that might get a stack check inserted.
+ __set_tls(main_thread.tls);
+
+ // Tell the kernel to clear our tid field when we exit, so we're like any other pthread.
+ // As a side-effect, this tells us our pid (which is the same as the main thread's tid).
+ main_thread.tid = __set_tid_address(&main_thread.tid);
+ main_thread.set_cached_pid(main_thread.tid);
+
+ // We don't want to free the main thread's stack even when the main thread exits
+ // because things like environment variables with global scope live on it.
+ // We also can't free the pthread_internal_t itself, since that lives on the main
+ // thread's stack rather than on the heap.
+ // The main thread has no mmap allocated space for stack or pthread_internal_t.
+ main_thread.mmap_size = 0;
+ pthread_attr_init(&main_thread.attr);
+ main_thread.attr.guard_size = 0; // The main thread has no guard page.
+ main_thread.attr.stack_size = 0; // User code should never see this; we'll compute it when asked.
+ // TODO: the main thread's sched_policy and sched_priority need to be queried.
+
+ __init_thread(&main_thread);
+ __init_tls(&main_thread);
+
+ // Store a pointer to the kernel argument block in a TLS slot to be
+ // picked up by the libc constructor.
+ main_thread.tls[TLS_SLOT_BIONIC_PREINIT] = &args;
+
+ __init_alternate_signal_stack(&main_thread);
+}