1/*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef KERNEL_ARGUMENT_BLOCK_H
18#define KERNEL_ARGUMENT_BLOCK_H
19
20#include <elf.h>
21#include <stdint.h>
22#include <sys/auxv.h>
23
24struct abort_msg_t;
25
26// When the kernel starts the dynamic linker, it passes a pointer to a block
27// of memory containing argc, the argv array, the environment variable array,
28// and the array of ELF aux vectors. This class breaks that block up into its
29// constituents for easy access.
30class KernelArgumentBlock {
31 public:
32  KernelArgumentBlock(void* raw_args) {
33    uint32_t* args = reinterpret_cast<uint32_t*>(raw_args);
34    argc = static_cast<int>(*args);
35    argv = reinterpret_cast<char**>(args + 1);
36    envp = argv + argc + 1;
37
38    // Skip over all environment variable definitions to find aux vector.
39    // The end of the environment block is marked by two NULL pointers.
40    char** p = envp;
41    while (*p != NULL) {
42      ++p;
43    }
44    ++p; // Skip second NULL;
45
46    auxv = reinterpret_cast<Elf32_auxv_t*>(p);
47  }
48
49  // Similar to ::getauxval but doesn't require the libc global variables to be set up,
50  // so it's safe to call this really early on. This function also lets you distinguish
51  // between the inability to find the given type and its value just happening to be 0.
52  unsigned long getauxval(unsigned long type, bool* found_match = NULL) {
53    for (Elf32_auxv_t* v = auxv; v->a_type != AT_NULL; ++v) {
54      if (v->a_type == type) {
55        if (found_match != NULL) {
56            *found_match = true;
57        }
58        return v->a_un.a_val;
59      }
60    }
61    if (found_match != NULL) {
62      *found_match = false;
63    }
64    return 0;
65  }
66
67  int argc;
68  char** argv;
69  char** envp;
70  Elf32_auxv_t* auxv;
71
72  abort_msg_t** abort_message_ptr;
73
74 private:
75  // Disallow copy and assignment.
76  KernelArgumentBlock(const KernelArgumentBlock&);
77  void operator=(const KernelArgumentBlock&);
78};
79
80#endif // KERNEL_ARGUMENT_BLOCK_H
81