Add full support for initing registers.

- Fixes a few bugs in untested functionality.
- Add tests for the way the register handling code is used.
- Fix a few tests that were not reaping child processes.

Bug: 23762183

Test: Ran unit tests on host (32 bit and 64 bit).
Test: Ran unit tests on angler (32 bit and 64 bit).
Change-Id: I573d6617b4f1561f6e8494d7213c52086d112d97
diff --git a/libunwindstack/AsmGetRegsX86_64.S b/libunwindstack/AsmGetRegsX86_64.S
new file mode 100644
index 0000000..4cd3b6f
--- /dev/null
+++ b/libunwindstack/AsmGetRegsX86_64.S
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2016 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.
+ */
+
+  .text
+  .global AsmGetRegs
+  .balign 16
+  .type AsmGetRegs, @function
+AsmGetRegs:
+  .cfi_startproc
+  movq %rax, (%rdi)
+  movq %rdx, 8(%rdi)
+  movq %rcx, 16(%rdi)
+  movq %rbx, 24(%rdi)
+  movq %rsi, 32(%rdi)
+  movq %rdi, 40(%rdi)
+  movq %rbp, 48(%rdi)
+
+  /* RSP */
+  lea 8(%rsp), %rax
+  movq %rax, 56(%rdi)
+
+  movq %r8, 64(%rdi)
+  movq %r9, 72(%rdi)
+  movq %r10, 80(%rdi)
+  movq %r11, 88(%rdi)
+  movq %r12, 96(%rdi)
+  movq %r13, 104(%rdi)
+  movq %r14, 112(%rdi)
+  movq %r15, 120(%rdi)
+
+  /* RIP */
+  movq (%rsp), %rax
+  movq %rax, 128(%rdi)
+  ret
+
+  .cfi_endproc
+  .size AsmGetRegs, .-AsmGetRegs