text: // Copyright 2019 Google LLC. All Rights Reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  // Seccomp BPF helper functions, modified from the Chromium OS version. The
  // original notice is below.
  //
  // Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
  // Author: Will Drewry <wad@chromium.org>
  //
  // The code may be used by anyone for any purpose,
  // and can serve as a starting point for developing
  // applications using prctl(PR_ATTACH_SECCOMP_FILTER).
  
  
  #include "sandboxed_api/sandbox2/util/bpf_helper.h"
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  int bpf_resolve_jumps(struct bpf_labels *labels,
  		      struct sock_filter *filter, size_t count)
  {
  	size_t i;
  
  	if (count < 1 || count > BPF_MAXINSNS)
  		return -1;
  	/*
  	* Walk it once, backwards, to build the label table and do fixups.
  	* Since backward jumps are disallowed by BPF, this is easy.
  	*/
  	for (i = 0; i < count; ++i) {
  		size_t offset = count - i - 1;
  		struct sock_filter *instr = &filter[offset];
  		if (instr->code != (BPF_JMP+BPF_JA))
  			continue;
  		switch ((instr->jt<<8)|instr->jf) {
  		case (JUMP_JT<<8)|JUMP_JF:
  			if (labels->labels[instr->k].location == 0xffffffff) {
  				fprintf(stderr, "Unresolved label: '%s'\n",
  					labels->labels[instr->k].label);
  				return 1;
  			}
  			instr->k = labels->labels[instr->k].location -
  				    (offset + 1);
  			instr->jt = 0;
  			instr->jf = 0;
  			continue;
  		case (LABEL_JT<<8)|LABEL_JF:
  			if (labels->labels[instr->k].location != 0xffffffff) {
  				fprintf(stderr, "Duplicate label use: '%s'\n",
  					labels->labels[instr->k].label);
  				return 1;
  			}
  			labels->labels[instr->k].location = offset;
  			instr->k = 0; /* fall through */
  			instr->jt = 0;
  			instr->jf = 0;
  			continue;
  		}
  	}
  	return 0;
  }
  
  /* Simple lookup table for labels. */
  __u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
  {
  	struct __bpf_label *begin = labels->labels, *end;
  	int id;
  
  	if (labels->count == BPF_LABELS_MAX) {
  		fprintf(stderr, "Too many labels\n");
  		exit(1);
  	}
  	if (labels->count == 0) {
  		begin->label = label;
  		begin->location = 0xffffffff;
  		labels->count++;
  		return 0;
  	}
  	end = begin + labels->count;
  	for (id = 0; begin < end; ++begin, ++id) {
  		if (!strcmp(label, begin->label))
  			return id;
  	}
  	begin->label = label;
  	begin->location = 0xffffffff;
  	labels->count++;
  	return id;
  }
  
  void seccomp_bpf_print(struct sock_filter *filter, size_t count)
  {
  	struct sock_filter *end = filter + count;
  	for ( ; filter < end; ++filter)
  		printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
  			filter->code, filter->jt, filter->jf, filter->k);
  }
  
  