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 <link.h>
22 #include <stdint.h>
23 #include <sys/auxv.h>
24 
25 #include "private/bionic_macros.h"
26 
27 struct abort_msg_t;
28 
29 // When the kernel starts the dynamic linker, it passes a pointer to a block
30 // of memory containing argc, the argv array, the environment variable array,
31 // and the array of ELF aux vectors. This class breaks that block up into its
32 // constituents for easy access.
33 class KernelArgumentBlock {
34  public:
KernelArgumentBlock(void * raw_args)35   KernelArgumentBlock(void* raw_args) {
36     uintptr_t* args = reinterpret_cast<uintptr_t*>(raw_args);
37     argc = static_cast<int>(*args);
38     argv = reinterpret_cast<char**>(args + 1);
39     envp = argv + argc + 1;
40 
41     // Skip over all environment variable definitions to find aux vector.
42     // The end of the environment block is marked by two NULL pointers.
43     char** p = envp;
44     while (*p != NULL) {
45       ++p;
46     }
47     ++p; // Skip second NULL;
48 
49     auxv = reinterpret_cast<ElfW(auxv_t)*>(p);
50   }
51 
52   // Similar to ::getauxval but doesn't require the libc global variables to be set up,
53   // so it's safe to call this really early on. This function also lets you distinguish
54   // between the inability to find the given type and its value just happening to be 0.
55   unsigned long getauxval(unsigned long type, bool* found_match = NULL) {
56     for (ElfW(auxv_t)* v = auxv; v->a_type != AT_NULL; ++v) {
57       if (v->a_type == type) {
58         if (found_match != NULL) {
59             *found_match = true;
60         }
61         return v->a_un.a_val;
62       }
63     }
64     if (found_match != NULL) {
65       *found_match = false;
66     }
67     return 0;
68   }
69 
70   int argc;
71   char** argv;
72   char** envp;
73   ElfW(auxv_t)* auxv;
74 
75   abort_msg_t** abort_message_ptr;
76 
77  private:
78   DISALLOW_COPY_AND_ASSIGN(KernelArgumentBlock);
79 };
80 
81 #endif // KERNEL_ARGUMENT_BLOCK_H
82