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
10namespace 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.
26struct 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__
63