chromium/sandbox/linux/bpf_dsl/codegen.h

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SANDBOX_LINUX_BPF_DSL_CODEGEN_H__
#define SANDBOX_LINUX_BPF_DSL_CODEGEN_H__

#include <stddef.h>
#include <stdint.h>

#include <map>
#include <tuple>
#include <vector>

#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);
//   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 { … };

}  // namespace sandbox

#endif  // SANDBOX_LINUX_BPF_DSL_CODEGEN_H__