diff options
Diffstat (limited to 'kernel/gdt.c')
| -rw-r--r-- | kernel/gdt.c | 112 |
1 files changed, 55 insertions, 57 deletions
diff --git a/kernel/gdt.c b/kernel/gdt.c index 1ee2042..8d1ac65 100644 --- a/kernel/gdt.c +++ b/kernel/gdt.c @@ -46,67 +46,63 @@ enum { SEG_end }; -static struct gdt_entry GDT[6]; +static struct gdt_entry GDT[SEG_end]; static struct tss_entry TSS; static struct lgdt_arg lgdt_arg; // probably doesn't need to be global static void gdt_prepare(); static void gdt_load(); +static void gdt_check(); static void gdt_prepare() { - // null segment - GDT[0].present = 0; - - // ring0 data - GDT[1].limit_low = 0xFFFF; - GDT[1].limit_high = 0xF; - GDT[1].gran = 1; // 4KB * 0xFFFFF = (almost) 4GB - - GDT[1].base_low = 0; - GDT[1].base_high = 0; - GDT[1].accessed = 0; - GDT[1].rw = 1; - GDT[1].conforming = 0; - GDT[1].code = 0; - GDT[1].codeordata = 1; - GDT[1].ring = 0; - GDT[1].present = 1; - GDT[1].long_mode = 0; // ??? - GDT[1].available = 1; // ??? - GDT[1].x32 = 1; + GDT[SEG_null].present = 0; + + GDT[SEG_r0data].limit_low = 0xFFFF; + GDT[SEG_r0data].limit_high = 0xF; + GDT[SEG_r0data].gran = 1; // 4KB * 0xFFFFF = (almost) 4GB + GDT[SEG_r0data].base_low = 0; + GDT[SEG_r0data].base_high = 0; + GDT[SEG_r0data].accessed = 0; + GDT[SEG_r0data].rw = 1; + GDT[SEG_r0data].conforming = 0; + GDT[SEG_r0data].code = 0; + GDT[SEG_r0data].codeordata = 1; + GDT[SEG_r0data].ring = 0; + GDT[SEG_r0data].present = 1; + GDT[SEG_r0data].long_mode = 0; // ??? + GDT[SEG_r0data].available = 1; // ??? + GDT[SEG_r0data].x32 = 1; // copy to r0 code - GDT[2] = GDT[1]; - GDT[2].code = 1; - - // r3 data & code - GDT[3] = GDT[1]; - GDT[3].ring = 3; - GDT[4] = GDT[2]; - GDT[3].ring = 3; - - { // tss - // TODO memset(&TSS, 0, sizeof(TSS)); - TSS.ss0 = 1 << 3; // kernel data segment - TSS.esp0 = (uint32_t) &stack_top; - - GDT[5].limit_low = sizeof(TSS); - GDT[5].base_low = (uint32_t) &TSS; - GDT[5].accessed = 1; // 0 for TSS - GDT[5].rw = 0; // 1 busy / 0 not busy - GDT[5].conforming = 0; // 0 for TSS - GDT[5].code = 1; // 32bit - GDT[5].codeordata = 0; // is a system entry - GDT[5].ring = 3; - GDT[5].present = 1; - GDT[5].limit_high = (sizeof(TSS) >> 16) & 0xf; - GDT[5].available = 0; // 0 for TSS - GDT[5].long_mode = 0; - GDT[5].x32 = 0; // idk - GDT[5].gran = 0; - GDT[5].base_high = (((uint32_t) &TSS) >> 24) & 0xff; - } + GDT[SEG_r0code] = GDT[SEG_r0data]; + GDT[SEG_r0code].code = SEG_r0data; + + GDT[SEG_r3data] = GDT[SEG_r0data]; + GDT[SEG_r3data].ring = 3; + GDT[SEG_r3code] = GDT[SEG_r0code]; + GDT[SEG_r3data].ring = 3; + + // tss + // TODO memset(&TSS, 0, sizeof(TSS)); + TSS.ss0 = SEG_r0data << SEG_r3data; // kernel data segment + TSS.esp0 = (uint32_t) &stack_top; + + GDT[SEG_TSS].limit_low = sizeof(TSS); + GDT[SEG_TSS].base_low = (uint32_t) &TSS; + GDT[SEG_TSS].accessed = 1; // 1 for TSS + GDT[SEG_TSS].rw = 0; // 1 busy / 0 not busy + GDT[SEG_TSS].conforming = 0; // 0 for TSS + GDT[SEG_TSS].code = 1; // 32bit + GDT[SEG_TSS].codeordata = 0; // is a system entry + GDT[SEG_TSS].ring = 3; + GDT[SEG_TSS].present = 1; + GDT[SEG_TSS].limit_high = (sizeof(TSS) >> 16) & 0xf; + GDT[SEG_TSS].available = 0; // 0 for TSS + GDT[SEG_TSS].long_mode = 0; + GDT[SEG_TSS].x32 = 0; // idk + GDT[SEG_TSS].gran = 0; + GDT[SEG_TSS].base_high = (((uint32_t) &TSS) >> 24) & 0xff; } static void gdt_load() { @@ -115,13 +111,15 @@ static void gdt_load() { asm("lgdt (%0)" : : "b" (&lgdt_arg)); } +static void gdt_check() { + tty_write("checking gdt...", 15); + asm("mov %0, %%ds;" + : : "r" (SEG_r0data << 3)); + tty_write("ok", 2); +} + void gdt_init() { gdt_prepare(); gdt_load(); - // check if the GDT was set up correctly - tty_write("checking gdt...", 15); - asm("mov $8, %%eax;" - "mov %%eax, %%ds;" - : : : "%eax"); - tty_write("ok", 2); + gdt_check(); } |