1 /* 2 * Task handling. 3 * 4 * Copyright (C) 2015, 2016 Paul Boddie <paul@boddie.org.uk> 5 * 6 * This program is free software: you can redistribute it and/or modify 7 * it under the terms of the GNU General Public License as published by 8 * the Free Software Foundation, either version 3 of the License, or 9 * (at your option) any later version. 10 * 11 * This program is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU General Public License for more details. 15 * 16 * You should have received a copy of the GNU General Public License 17 * along with this program. If not, see <http://www.gnu.org/licenses/>. 18 */ 19 20 #include "cpu.h" 21 #include "cpu_op.h" 22 #include "memory.h" 23 #include "mips.h" 24 #include "paging.h" 25 #include "tasks.h" 26 27 /* Task tables and data. */ 28 29 static u32 stack_pointers[max_tasks]; 30 static u32 registers[max_tasks][32]; 31 32 u8 current_task; 33 u32 *current_stack_pointer; 34 u32 *current_registers; 35 36 /* A reference to locations for the symbol tables. */ 37 38 extern u32 _got_start, _got_copy_start, _got_copy_end; 39 40 /* A reference to the start of the payload and end of memory locations. */ 41 42 extern u32 _payload_start, _memory_end; 43 44 /* Task management functions. */ 45 46 void init_tasks() 47 { 48 current_task = 1; 49 init_task(); 50 } 51 52 void init_task() 53 { 54 current_stack_pointer = &stack_pointers[current_task]; 55 current_registers = registers[current_task]; 56 } 57 58 void start_task(unsigned short task, void (*function)(), u32 args[], u8 nargs) 59 { 60 u32 virtual, physical, address; 61 62 /* 63 Each task employs a stack at a multiple of the given start address in 64 physical memory, but at the same address in virtual memory. Task zero 65 is never started. 66 */ 67 68 virtual = STAGE2_TASK_STACK; 69 physical = STAGE2_TASK_STACK - STAGE2_TASK_STACK_SIZE * task; 70 71 init_page_table(STAGE2_PAGE_TABLE, 72 previous_page(virtual, STAGE2_PAGESIZE), 73 previous_page(physical, STAGE2_PAGESIZE), 74 STAGE2_PAGESIZE, TLB_WRITE, task); 75 76 /* 77 Subtract from the stack pointer to prevent the called function from 78 reaching into unmapped memory. 79 */ 80 81 stack_pointers[task] = virtual - 12; 82 83 /* 84 Set the registers for the new task, initialising the global pointer and 85 return address. 86 */ 87 88 init_registers(registers[task], (u32) &_got_copy_start, function, args, nargs); 89 90 /* Map the global object table for the task. */ 91 92 init_page_table(STAGE2_PAGE_TABLE, 93 user_address((u32) &_got_start), 94 user_address((u32) &_got_copy_start), 95 STAGE2_PAGESIZE, TLB_READ, task); 96 97 /* Map all shared pages for the task. First, the read-only code region. */ 98 99 for (address = (u32) &_payload_start; 100 address < (u32) &_got_start; 101 address = next_page(address, STAGE2_PAGESIZE)) 102 { 103 init_page_table(STAGE2_PAGE_TABLE, 104 user_address(address), 105 user_address(address), 106 STAGE2_PAGESIZE, TLB_READ, task); 107 } 108 109 /* Make the pages after the code writable. */ 110 111 for (address = next_page((u32) &_got_copy_end, STAGE2_PAGESIZE); 112 address < (u32) &_memory_end; 113 address = next_page(address, STAGE2_PAGESIZE)) 114 { 115 init_page_table(STAGE2_PAGE_TABLE, 116 user_address(address), 117 user_address(address), 118 STAGE2_PAGESIZE, TLB_WRITE, task); 119 } 120 } 121 122 void start_task_now() 123 { 124 invoke_task(current_task, current_registers, current_stack_pointer); 125 } 126 127 void switch_task() 128 { 129 /* Switch the current task. */ 130 131 current_task++; 132 if (current_task == max_tasks) current_task = 1; 133 init_task(); 134 }