sandbox: move Codegen into bpf_dsl directory

sandbox/linux/seccomp-bpf/codegen.h

-// Copyright (c) 2012 The Chromium 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 SANDBOX_LINUX_SECCOMP_BPF_CODEGEN_H__
-#define SANDBOX_LINUX_SECCOMP_BPF_CODEGEN_H__
-
-#include <stddef.h>
-#include <stdint.h>
-
-#include <map>
-#include <vector>
-
-#include "base/macros.h"
-#include "base/tuple.h"
-#include "sandbox/sandbox_export.h"
-
-struct sock_filter;
-
-namespace sandbox {
-
-// The code generator implements a basic assembler that can convert a
-// graph of BPF instructions into a well-formed array of BPF
-// instructions. Most notably, it ensures that jumps are always
-// forward and don't exceed the limit of 255 instructions imposed by
-// the instruction set.
-//
-// Callers would typically create a new CodeGen object and then use it
-// to build a DAG of instruction nodes. They'll eventually call
-// Compile() to convert this DAG to a Program.
-//
-//   CodeGen gen;
-//   CodeGen::Node allow, branch, dag;
-//
-//   allow =
-//     gen.MakeInstruction(BPF_RET+BPF_K,
-//                         ErrorCode(ErrorCode::ERR_ALLOWED).err()));
-//   branch =
-//     gen.MakeInstruction(BPF_JMP+BPF_EQ+BPF_K, __NR_getpid,
-//                         Trap(GetPidHandler, NULL), allow);
-//   dag =
-//     gen.MakeInstruction(BPF_LD+BPF_W+BPF_ABS,
-//                         offsetof(struct arch_seccomp_data, nr), branch);
-//
-//   // Simplified code follows; in practice, it is important to avoid calling
-//   // any C++ destructors after starting the sandbox.
-//   CodeGen::Program program;
-//   gen.Compile(dag, program);
-//   const struct sock_fprog prog = {
-//     static_cast<unsigned short>(program->size()), &program[0] };
-//   prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog);
-//
-class SANDBOX_EXPORT CodeGen {
- public:
-  // A vector of BPF instructions that need to be installed as a filter
-  // program in the kernel.
-  typedef std::vector<struct sock_filter> Program;
-
-  // Node represents a node within the instruction DAG being compiled.
-  using Node = Program::size_type;
-
-  // kNullNode represents the "null" node; i.e., the reserved node
-  // value guaranteed to not equal any actual nodes.
-  static const Node kNullNode = -1;
-
-  CodeGen();
-  ~CodeGen();
-
-  // MakeInstruction creates a node representing the specified
-  // instruction, or returns and existing equivalent node if one
-  // exists. For details on the possible parameters refer to
-  // https://www.kernel.org/doc/Documentation/networking/filter.txt.
-  // TODO(mdempsky): Reconsider using default arguments here.
-  Node MakeInstruction(uint16_t code,
-                       uint32_t k,
-                       Node jt = kNullNode,
-                       Node jf = kNullNode);
-
-  // Compile linearizes the instruction DAG rooted at |head| into a
-  // program that can be executed by a BPF virtual machine.
-  void Compile(Node head, Program* program);
-
- private:
-  using MemoKey = Tuple<uint16_t, uint32_t, Node, Node>;
-  struct MemoKeyLess {
-    bool operator()(const MemoKey& lhs, const MemoKey& rhs) const;
-  };
-
-  // AppendInstruction adds a new instruction, ensuring that |jt| and
-  // |jf| are within range as necessary for |code|.
-  Node AppendInstruction(uint16_t code, uint32_t k, Node jt, Node jf);
-
-  // WithinRange returns a node equivalent to |next| that is at most
-  // |range| instructions away from the (logical) beginning of the
-  // program.
-  Node WithinRange(Node next, size_t range);
-
-  // Append appends a new instruction to the physical end (i.e.,
-  // logical beginning) of |program_|.
-  Node Append(uint16_t code, uint32_t k, size_t jt, size_t jf);
-
-  // Offset returns how many instructions exist in |program_| after |target|.
-  size_t Offset(Node target) const;
-
-  // NOTE: program_ is the compiled program in *reverse*, so that
-  // indices remain stable as we add instructions.
-  Program program_;
-
-  // equivalent_ stores the most recent semantically-equivalent node for each
-  // instruction in program_. A node is defined as semantically-equivalent to N
-  // if it has the same instruction code and constant as N and its successor
-  // nodes (if any) are semantically-equivalent to N's successor nodes, or
-  // if it's an unconditional jump to a node semantically-equivalent to N.
-  std::vector<Node> equivalent_;
-
-  std::map<MemoKey, Node, MemoKeyLess> memos_;
-
-  DISALLOW_COPY_AND_ASSIGN(CodeGen);
-};
-
-}  // namespace sandbox
-
-#endif  // SANDBOX_LINUX_SECCOMP_BPF_CODEGEN_H__