23 /* Size of kernel static code and data, in 4 kB pages. */
26 /* Amount of physical memory, in 4 kB pages. */
29 static void gdt_init (void);
30 void power_off (void);
33 main_thread (void *aux UNUSED)
35 printk ("execute=%d\n", (int) thread_execute ("a.out"));
41 extern char _text, _end, __bss_start;
44 /* Clear out the BSS segment. */
45 memset (&__bss_start, 0, &_end - &__bss_start);
50 /* Calculate how much RAM the kernel uses, and find out from
51 the bootloader how much RAM this machine has. */
52 kernel_pages = (&_end - &_text + 4095) / 4096;
53 ram_pages = *(uint32_t *) (0x7e00 - 8);
55 printk ("Initializing nachos-x86, %d kB RAM detected.\n",
58 /* Memory from the end of the kernel through the end of memory
59 is free. Give it to the page allocator. */
60 palloc_init ((void *) (KERN_BASE + kernel_pages * PGSIZE),
61 (void *) (PHYS_BASE + ram_pages * PGSIZE));
79 t = thread_create ("main", main_thread, NULL);
87 make_seg_desc (uint32_t base,
89 enum seg_system system,
92 enum seg_granularity granularity)
94 uint32_t e0 = ((limit & 0xffff) /* Limit 15:0. */
95 | (base << 16)); /* Base 15:0. */
96 uint32_t e1 = (((base >> 16) & 0xff) /* Base 23:16. */
97 | ( system << 12) /* 0=system, 1=code/data. */
98 | ( type << 8) /* Segment type. */
99 | (dpl << 13) /* Descriptor privilege. */
100 | (1 << 15) /* Present. */
101 | (limit & 0xf0000) /* Limit 16:19. */
102 | (1 << 22) /* 32-bit segment. */
103 | ( granularity << 23) /* Byte/page granularity. */
104 | (base & 0xff000000)); /* Base 31:24. */
105 return e0 | ((uint64_t) e1 << 32);
109 make_code_desc (int dpl)
111 return make_seg_desc (0, 0xfffff, SYS_CODE_DATA, TYPE_CODE | TYPE_READABLE,
116 make_data_desc (int dpl)
118 return make_seg_desc (0, 0xfffff, SYS_CODE_DATA, TYPE_WRITABLE,
123 make_tss_desc (uint32_t base)
125 return make_seg_desc (base, 0x67, SYS_SYSTEM, TYPE_TSS_32_A, 0, GRAN_BYTE);
128 uint64_t gdt[SEL_CNT];
132 /* Sets up a proper GDT. The bootstrap loader's GDT didn't
133 include user-mode selectors or a TSS. */
137 uint64_t gdtr_operand;
139 /* Our TSS is never used in a call gate or task gate, so only a
140 few fields of it are ever referenced, and those are the only
141 ones we initialize. */
142 tss = palloc_get (PAL_ASSERT | PAL_ZERO);
143 tss->esp0 = (uint32_t) ptov(0x20000);
144 tss->ss0 = SEL_KDSEG;
145 tss->bitmap = 0xdfff;
147 /* Initialize GDT. */
148 gdt[SEL_NULL / sizeof *gdt] = 0;
149 gdt[SEL_KCSEG / sizeof *gdt] = make_code_desc (0);
150 gdt[SEL_KDSEG / sizeof *gdt] = make_data_desc (0);
151 gdt[SEL_UCSEG / sizeof *gdt] = make_code_desc (3);
152 gdt[SEL_UDSEG / sizeof *gdt] = make_data_desc (3);
153 gdt[SEL_TSS / sizeof *gdt] = make_tss_desc (vtop (tss));
156 gdtr_operand = make_dtr_operand (sizeof gdt - 1, gdt);
157 asm volatile ("lgdt %0" :: "m" (gdtr_operand));
158 asm volatile ("ltr %w0" :: "r" (SEL_TSS));
164 const char s[] = "Shutdown";
167 printk ("Powering off...\n");
168 for (p = s; *p != '\0'; p++)