[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 <ucontext.h>
+
+#include "src/base/build_config.h"
+
 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;
+#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);
+
+/// 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();
+
+bool EnableTrapHandler();

[Mark Mentovai, 2017/02/09 17:39:41]

It sounds like this should be called ShouldEnableTrapHandler() or
IsTrapHandlerSupported(). EnableTrapHandler() sounds like it does the enabling,
but that’s not what this does.

[Eric Holk, 2017/02/15 02:02:45]

Agreed. I'll go with ShouldEnableTrapHandler.

Done.

+bool RegisterDefaultSignalHandler();

[Mark Mentovai, 2017/02/09 17:39:41]

I find it a little weird that this function and the next one are declared here
instead of having a signal-handler.h, when they’re defined in signal-handler.cc.
Was there a particular rationale for that?

[Eric Holk, 2017/02/15 02:02:45]

The original idea was that trap-handler.h provided the external interface that
V8 would use to communicate with the trap handling facilities, trap-handler.cc
provided the implementation of these, and signal-handler.cc was for the
Linux-specific signal handling code. As this CL has evolved, this naming doesn't
make as much sense anymore.

Here's the new naming:

* trap-handler.h - Trap handler interface for V8.
* trap-handler-internal.h - Declarations that are shared between the various
files in src/trap-handler/
* handler-outside.cc - Trap handler code that does not run in the signal
handler, such as data structure maintenance. This is code that's called by the
rest of V8.
* handler-inside.cc - Trap handler code that runs from within the signal
handler.
* handler-shared.cc - Code that is used by both handler-inside.cc and
handler-outside.cc. Because it includes code that is called from the signal
handler, it needs to be subject to the same dependency rules as
handler-inside.cc.

In general, I've tried to use the phrase "trap handling" to refer to the overall
OS/hardware-based bounds check feature, and "signal handling" to refer to the
aspects of trap handling that are specific to Linux signals.

+
+#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_