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 11 namespace playground2 { 12 13 // The fields in this structure have the same meaning as the corresponding 14 // fields in "struct sock_filter". See <linux/filter.h> for a lot more 15 // detail. 16 // code -- Opcode of the instruction. This is typically a bitwise 17 // combination BPF_XXX values. 18 // k -- Operand; BPF instructions take zero or one operands. Operands 19 // are 32bit-wide constants, if present. They can be immediate 20 // values (if BPF_K is present in "code_"), addresses (if BPF_ABS 21 // is present in "code_"), or relative jump offsets (if BPF_JMP 22 // and BPF_JA are present in "code_"). 23 // jt, jf -- all conditional jumps have a 8bit-wide jump offset that allows 24 // jumps of up to 256 instructions forward. Conditional jumps are 25 // identified by BPF_JMP in "code_", but the lack of BPF_JA. 26 // Conditional jumps have a "t"rue and "f"alse branch. 27 struct Instruction { 28 // Constructor for an non-jumping instruction or for an unconditional 29 // "always" jump. 30 Instruction(uint16_t c, uint32_t parm, Instruction *n) : 31 code(c), next(n), k(parm) { } 32 33 // Constructor for a conditional jump instruction. 34 Instruction(uint16_t c, uint32_t parm, Instruction *jt, Instruction *jf) : 35 code(c), jt_ptr(jt), jf_ptr(jf), k(parm) { } 36 37 uint16_t code; 38 union { 39 // When code generation is complete, we will have computed relative 40 // branch targets that are in the range 0..255. 41 struct { 42 uint8_t jt, jf; 43 }; 44 45 // While assembling the BPF program, we use pointers for branch targets. 46 // Once we have computed basic blocks, these pointers will be entered as 47 // keys in a TargetsToBlocks map and should no longer be dereferenced 48 // directly. 49 struct { 50 Instruction *jt_ptr, *jf_ptr; 51 }; 52 53 // While assembling the BPF program, non-jumping instructions are linked 54 // by the "next_" pointer. This field is no longer needed when we have 55 // computed basic blocks. 56 Instruction *next; 57 }; 58 uint32_t k; 59 }; 60 61 } // namespace 62 63 #endif // SANDBOX_LINUX_SECCOMP_BPF_INSTRUCTION_H__ 64
