Reland Implement .eh_frame writer and disassembler.

src/x64/eh-frame-x64.h

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_X64_UNWINDING_INFO_X64_H_
+#define V8_X64_UNWINDING_INFO_X64_H_
+
+#include "src/macro-assembler.h"
+
+namespace v8 {
+namespace internal {
+
+static const Register& kInitialBaseRegister = rsp;

[rmcilroy, 2016/06/30 15:23:11]

Don't use const references. Just use the register code if you can't create a
static const Register.

[Stefano Sanfilippo, 2016/07/04 18:21:15]

I did away completely with this bit in the refactoring, removed.

+static const int kInitialBaseOffset = 8;
+static const int kDataAlignmentFactor = -8;

[rmcilroy, 2016/06/30 15:23:11]

Curious, why is this negative, seems pretty strange?

[Stefano Sanfilippo, 2016/07/04 18:21:15]

It's negative to reflect the fact that the stack grows downwards. That is, each
slot has an address -8 bytes "larger" than the previous.

+#ifdef ENABLE_DISASSEMBLER
+static const int kInitialStateOffsetInCIE = 19;

[rmcilroy, 2016/06/30 15:23:11]

This is always 19 on all platforms (the header is always be the same size), just
define directly in the disassemble directives function.

[Stefano Sanfilippo, 2016/07/04 18:21:15]

This bit became an arch-independent constant now that we have a WriteCIE()
method, so it has been removed. 

+#endif
+
+static const byte kCIE[] = {
+    0x18, 0x00, 0x00, 0x00,  // Size of the CIE
+    0x00, 0x00, 0x00, 0x00,  // CIE identifier, always 0
+    3,                       // CIE version 3
+    0x7a, 0x4c, 0x52, 0x00,  // Augmentation string zLR
+    1,                       // Code alignment factor
+    0x78,                    // Data alignment factor (-8 SLEB encoded)
+    16,                      // Return address register: rip (r16)
+    0x02,                    // Length of augmentation data
+    0xff,                    // No LSDA
+    0x1b,                    // FDE pointers encoding: kSData4 | kPcRel

[rmcilroy, 2016/06/30 15:23:11]

The CIE is almost identical for every platform (the only differences AFAIKS is
the size, alignment factor and return address register. Could you split up the
CIE into the header bit and the augmentation data. I also think you should write
these in the same way as you write the FDE, and only define the constants which
are different in this file (some of which, e.g., kDataAlignmentFactor, are
already here).

[Stefano Sanfilippo, 2016/07/04 18:21:15]

Done.

+    // Initial state
+    0x0c, 7, kInitialBaseOffset,  // base = rsp+8
+    0x90, 1,                      // rip saved at (base - 8)
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif