[XRay] Implement `llvm-xray extract`, start of the llvm-xray tool

Usage:

  llvm-xray extract <object file> [-o <filename or '-'>]

The tool gets the XRay instrumentation map from an object file and turns
it into YAML.  We first support ELF64 sleds on x86_64 binaries, with
provision for supporting other supported platforms and formats later.

This is the first of a many-part change to fully implement the
`llvm-xray` tool.

We also define a subcommand registration and dispatch mechanism to be
used by other further subcommand implementations for llvm-xray.

Diffusion Revision: https://reviews.llvm.org/D21987

llvm-svn: 285165

1 files changed, 41 insertions, 0 deletions

diff --git a/llvm/tools/llvm-xray/xray-registry.h b/llvm/tools/llvm-xray/xray-registry.h
new file mode 100644
index 00000000000..6eab016273f
--- /dev/null
+++ b/llvm/tools/llvm-xray/xray-registry.h
@@ -0,0 +1,41 @@
+//===- xray-registry.h - Define registry mechanism for commands. ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Implement a simple subcommand registry.
+//
+//===----------------------------------------------------------------------===//
+#ifndef TOOLS_LLVM_XRAY_XRAY_REGISTRY_H
+#define TOOLS_LLVM_XRAY_XRAY_REGISTRY_H
+
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Error.h"
+
+namespace llvm {
+namespace xray {
+
+// Use |CommandRegistration| as a global initialiser that registers a function
+// and associates it with |SC|. This requires that a command has not been
+// registered to a given |SC|.
+//
+// Usage:
+//
+//   // At namespace scope.
+//   static CommandRegistration Unused(&MySubCommand, [] { ... });
+//
+struct CommandRegistration {
+  CommandRegistration(cl::SubCommand *SC, std::function<Error()> Command);
+};
+
+// Requires that |SC| is not null and has an associated function to it.
+std::function<Error()> dispatch(cl::SubCommand *SC);
+
+} // namespace xray
+} // namespace llvm
+
+#endif // TOOLS_LLVM_XRAY_XRAY_REGISTRY_H