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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 <stdint.h>
     22 #include <sys/auxv.h>
     23 
     24 struct 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.
     30 class 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