[wasm] Initial signal handler

src/trap-handler/trap-handler.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_TRAP_HANDLER_H_
 #define V8_TRAP_HANDLER_H_
 
+#include <signal.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "src/base/build_config.h"
+#include "src/globals.h"
+
+#if V8_OS_LINUX
+#include <ucontext.h>
+#endif
+
 namespace v8 {
 namespace internal {
 namespace trap_handler {
 
+// TODO(eholk): Support trap handlers on other platforms.
+#if V8_TARGET_ARCH_X64 && V8_OS_LINUX
+#define V8_TRAP_HANDLER_SUPPORTED 1
+const bool kTrapHandlerSupported = true;

[titzer, 2017/02/20 09:50:08]

why not just move this down to:

const bool kTrapHandlerSupported = V8_TRAP_HANDLER_SUPPORTED?

Or better yet, just always use the #define instead of the constant?

[Eric Holk, 2017/02/23 02:16:57]

Originally I thought there was some good reason for the constant, but I don't
think there is. I've removed it now.

Done.

+#else
+#define V8_TRAP_HANDLER_SUPPORTED 0
+const bool kTrapHandlerSupported = false;
+#endif
+
 struct ProtectedInstructionData {
   // The offset of this instruction from the start of its code object.
   intptr_t instr_offset;
 
   // The offset of the landing pad from the start of its code object.
   //
   // TODO(eholk): Using a single landing pad and store parameters here.
   intptr_t landing_offset;
 };
 
+/// Adjusts the base code pointer.
+void UpdateCodePointer(int index, void* base);

[titzer, 2017/02/20 09:50:08]

We could use a more specific name here, because it's not clear what code pointer
this refers to.

[Eric Holk, 2017/02/23 02:16:57]

How about UpdateHandlerDataCodePointer?

Done.

+
+/// Adds the handler data to the place where the signal handler will find it.
+///
+/// This returns a number that can be used to identify the handler data to
+/// UpdateCodePointer and ReleaseHandlerData, or -1 on failure.
+int RegisterHandlerData(void* base, size_t size,
+                        size_t num_protected_instructions,
+                        ProtectedInstructionData* protected_instructions);
+
+/// Removes the data from the master list and frees any memory, if necessary.
+void ReleaseHandlerData(int index);
+
+void SetThreadInWasm();
+void ClearThreadInWasm();
+
+bool IsThreadInWasm();
+
+V8_EXPORT_PRIVATE bool ShouldEnableTrapHandler();

[titzer, 2017/02/20 09:50:08]

Uses of this method read kinda funny. Maybe

UseTrapHandler?
TrapHandlerEnabled?

[Eric Holk, 2017/02/23 02:16:57]

I went with UseTrapHandler.

Done.

+bool RegisterDefaultSignalHandler();
+
+#if V8_OS_LINUX
+bool TryHandleSignal(int signum, siginfo_t* info, ucontext_t* context);
+#endif  // V8_OS_LINUX
+
 }  // namespace trap_handler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TRAP_HANDLER_H_