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: KernelArgumentBlock(void * raw_args)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