sandbox/linux/seccomp-bpf/instruction.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef SANDBOX_LINUX_SECCOMP_BPF_INSTRUCTION_H__
   6 #define SANDBOX_LINUX_SECCOMP_BPF_INSTRUCTION_H__
   7
   8 #include <stdint.h>
   9
  10 namespace sandbox {
  11
  12 // The fields in this structure have the same meaning as the corresponding
  13 // fields in "struct sock_filter". See <linux/filter.h> for a lot more
  14 // detail.
  15 // code     -- Opcode of the instruction. This is typically a bitwise
  16 //             combination BPF_XXX values.
  17 // k        -- Operand; BPF instructions take zero or one operands. Operands
  18 //             are 32bit-wide constants, if present. They can be immediate
  19 //             values (if BPF_K is present in "code_"), addresses (if BPF_ABS
  20 //             is present in "code_"), or relative jump offsets (if BPF_JMP
  21 //             and BPF_JA are present in "code_").
  22 // jt, jf   -- all conditional jumps have a 8bit-wide jump offset that allows
  23 //             jumps of up to 256 instructions forward. Conditional jumps are
  24 //             identified by BPF_JMP in "code_", but the lack of BPF_JA.
  25 //             Conditional jumps have a "t"rue and "f"alse branch.
  26 struct Instruction {
  27   // Constructor for an non-jumping instruction or for an unconditional
  28   // "always" jump.
  29   Instruction(uint16_t c, uint32_t parm, Instruction* n)
  30       : code(c), next(n), k(parm) {}
  31
  32   // Constructor for a conditional jump instruction.
  33   Instruction(uint16_t c, uint32_t parm, Instruction* jt, Instruction* jf)
  34       : code(c), jt_ptr(jt), jf_ptr(jf), k(parm) {}
  35
  36   uint16_t code;
  37   union {
  38     // When code generation is complete, we will have computed relative
  39     // branch targets that are in the range 0..255.
  40     struct {
  41       uint8_t jt, jf;
  42     };
  43
  44     // While assembling the BPF program, we use pointers for branch targets.
  45     // Once we have computed basic blocks, these pointers will be entered as
  46     // keys in a TargetsToBlocks map and should no longer be dereferenced
  47     // directly.
  48     struct {
  49       Instruction* jt_ptr, *jf_ptr;
  50     };
  51
  52     // While assembling the BPF program, non-jumping instructions are linked
  53     // by the "next_" pointer. This field is no longer needed when we have
  54     // computed basic blocks.
  55     Instruction* next;
  56   };
  57   uint32_t k;
  58 };
  59
  60 }  // namespace sandbox
  61
  62 #endif  // SANDBOX_LINUX_SECCOMP_BPF_INSTRUCTION_H__