blob: 0fc8123280eb07d76d44ff1f4c566d7af7dce140 [file] [log] [blame]
// 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.
#include <stdint.h>
namespace playground2 {
// The fields in this structure have the same meaning as the corresponding
// fields in "struct sock_filter". See <linux/filter.h> for a lot more
// detail.
// code -- Opcode of the instruction. This is typically a bitwise
// combination BPF_XXX values.
// k -- Operand; BPF instructions take zero or one operands. Operands
// are 32bit-wide constants, if present. They can be immediate
// values (if BPF_K is present in "code_"), addresses (if BPF_ABS
// is present in "code_"), or relative jump offsets (if BPF_JMP
// and BPF_JA are present in "code_").
// jt, jf -- all conditional jumps have a 8bit-wide jump offset that allows
// jumps of up to 256 instructions forward. Conditional jumps are
// identified by BPF_JMP in "code_", but the lack of BPF_JA.
// Conditional jumps have a "t"rue and "f"alse branch.
struct Instruction {
// Constructor for an non-jumping instruction or for an unconditional
// "always" jump.
Instruction(uint16_t c, uint32_t parm, Instruction *n) :
code(c), next(n), k(parm) { }
// Constructor for a conditional jump instruction.
Instruction(uint16_t c, uint32_t parm, Instruction *jt, Instruction *jf) :
code(c), jt_ptr(jt), jf_ptr(jf), k(parm) { }
uint16_t code;
union {
// When code generation is complete, we will have computed relative
// branch targets that are in the range 0..255.
struct {
uint8_t jt, jf;
// While assembling the BPF program, we use pointers for branch targets.
// Once we have computed basic blocks, these pointers will be entered as
// keys in a TargetsToBlocks map and should no longer be dereferenced
// directly.
struct {
Instruction *jt_ptr, *jf_ptr;
// While assembling the BPF program, non-jumping instructions are linked
// by the "next_" pointer. This field is no longer needed when we have
// computed basic blocks.
Instruction *next;
uint32_t k;
} // namespace