24 /* Size of kernel static code and data, in 4 kB pages. */
27 /* Amount of physical memory, in 4 kB pages. */
30 static void gdt_init (void);
31 void power_off (void);
34 main_thread (void *aux UNUSED)
37 thread_execute ("a.out");
43 extern char _text, _end, __bss_start;
46 /* Clear out the BSS segment. */
47 memset (&__bss_start, 0, &_end - &__bss_start);
52 /* Calculate how much RAM the kernel uses, and find out from
53 the bootloader how much RAM this machine has. */
54 kernel_pages = (&_end - &_text + 4095) / 4096;
55 ram_pages = *(uint32_t *) (0x7e00 - 6);
57 printk ("Initializing nachos-x86, %d kB RAM detected.\n",
60 /* Memory from the end of the kernel through the end of memory
61 is free. Give it to the page allocator. */
62 palloc_init ((void *) (KERN_BASE + kernel_pages * PGSIZE),
63 (void *) (PHYS_BASE + ram_pages * PGSIZE));
80 t = thread_create ("main", main_thread, NULL);
88 make_seg_desc (uint32_t base,
90 enum seg_system system,
93 enum seg_granularity granularity)
95 uint32_t e0 = ((limit & 0xffff) /* Limit 15:0. */
96 | (base << 16)); /* Base 15:0. */
97 uint32_t e1 = (((base >> 16) & 0xff) /* Base 23:16. */
98 | (system << 12) /* 0=system, 1=code/data. */
99 | (type << 8) /* Segment type. */
100 | (dpl << 13) /* Descriptor privilege. */
101 | (1 << 15) /* Present. */
102 | (limit & 0xf0000) /* Limit 16:19. */
103 | (1 << 22) /* 32-bit segment. */
104 | (granularity << 23) /* Byte/page granularity. */
105 | (base & 0xff000000)); /* Base 31:24. */
106 return e0 | ((uint64_t) e1 << 32);
110 make_code_desc (int dpl)
112 return make_seg_desc (0, 0xfffff, SYS_CODE_DATA, TYPE_CODE | TYPE_READABLE,
117 make_data_desc (int dpl)
119 return make_seg_desc (0, 0xfffff, SYS_CODE_DATA, TYPE_WRITABLE,
124 make_tss_desc (void *vaddr)
126 return make_seg_desc ((uint32_t) vaddr,
127 0x67, SYS_SYSTEM, TYPE_TSS_32_A, 0, GRAN_BYTE);
130 uint64_t gdt[SEL_CNT];
134 /* Sets up a proper GDT. The bootstrap loader's GDT didn't
135 include user-mode selectors or a TSS. */
139 uint64_t gdtr_operand;
141 /* Our TSS is never used in a call gate or task gate, so only a
142 few fields of it are ever referenced, and those are the only
143 ones we initialize. */
144 tss = palloc_get (PAL_ASSERT | PAL_ZERO);
145 tss->esp0 = (uint32_t) ptov(0x20000);
146 tss->ss0 = SEL_KDSEG;
147 tss->bitmap = 0xdfff;
149 /* Initialize GDT. */
150 gdt[SEL_NULL / sizeof *gdt] = 0;
151 gdt[SEL_KCSEG / sizeof *gdt] = make_code_desc (0);
152 gdt[SEL_KDSEG / sizeof *gdt] = make_data_desc (0);
153 gdt[SEL_UCSEG / sizeof *gdt] = make_code_desc (3);
154 gdt[SEL_UDSEG / sizeof *gdt] = make_data_desc (3);
155 gdt[SEL_TSS / sizeof *gdt] = make_tss_desc (tss);
158 gdtr_operand = make_dtr_operand (sizeof gdt - 1, gdt);
159 asm volatile ("lgdt %0" :: "m" (gdtr_operand));
160 asm volatile ("ltr %w0" :: "r" (SEL_TSS));
166 const char s[] = "Shutdown";
169 printk ("Powering off...\n");
170 for (p = s; *p != '\0'; p++)