Linux sandbox: Remove CodeGen::JoinInstructions.

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 <map>
 #include <vector>
 
@@ skipping 12 matching lines @@
 
 // The code generator instantiates a basic compiler that can convert a
 // graph of BPF instructions into a well-formed stream 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 Instructions. They'll eventually call Compile() to convert
 // this DAG to a SandboxBPF::Program.
 //
-// Instructions can be chained at the time when they are created, or they
-// can be joined later by calling JoinInstructions().
+//   CodeGen gen;
+//   Instruction *allow, *branch, *dag;
 //
-//   CodeGen gen;
-//   Instruction *dag, *branch;
+//   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 =
-//     gen.MakeInstruction(BPF_JMP+BPF_EQ+BPF_K, __NR_getpid,
-//                         Trap(GetPidHandler, NULL), NULL);
-//   gen.JoinInstructions(branch,
-//     gen.MakeInstruction(BPF_RET+BPF_K,
-//                         ErrorCode(ErrorCode::ERR_ALLOWED).err()));
+//                         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.
 //   SandboxBPF::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 {
@@ skipping 10 matching lines @@
   // deleted.
   // For details on the possible parameters refer to <linux/filter.h>
   Instruction* MakeInstruction(uint16_t code,
                                uint32_t k,
                                Instruction* next = NULL);
   Instruction* MakeInstruction(uint16_t code,
                                uint32_t k,
                                Instruction* jt,
                                Instruction* jf);
 
-  // Join two (sequences of) instructions. This is useful, if the "next"
-  // parameter had not originally been given in the call to MakeInstruction(),
-  // or if a (conditional) jump still has an unsatisfied target.
-  void JoinInstructions(Instruction* head, Instruction* tail);
-
   // Traverse the graph of instructions and visit each instruction once.
   // Traversal order is implementation-defined. It is acceptable to make
   // changes to the graph from within the callback function. These changes
   // do not affect traversal.
   // The "fnc" function gets called with both the instruction and the opaque
   // "aux" pointer.
   void Traverse(Instruction*, void (*fnc)(Instruction*, void* aux), void* aux);
 
   // Compiles the graph of instructions into a BPF program that can be passed
   // to the kernel. Please note that this function modifies the graph in place
@@ skipping 58 matching lines @@
   BasicBlocks basic_blocks_;
 
   // Compile() must only ever be called once as it makes destructive changes
   // to the DAG.
   bool compiled_;
 };
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_LINUX_SECCOMP_BPF_CODEGEN_H__