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      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:
     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