From 9dbc5231dd738d97eea13f8ecf9005e5b78ea0d3 Mon Sep 17 00:00:00 2001 From: Nic Gaffney Date: Sun, 17 Dec 2023 13:21:21 -0600 Subject: Restructured --- src/kernel/gdt/compile_flags.txt | 1 + src/kernel/gdt/gdt.c | 56 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 57 insertions(+) create mode 100644 src/kernel/gdt/compile_flags.txt create mode 100644 src/kernel/gdt/gdt.c (limited to 'src/kernel/gdt') diff --git a/src/kernel/gdt/compile_flags.txt b/src/kernel/gdt/compile_flags.txt new file mode 100644 index 0000000..2af49c7 --- /dev/null +++ b/src/kernel/gdt/compile_flags.txt @@ -0,0 +1 @@ +-I../../include/ diff --git a/src/kernel/gdt/gdt.c b/src/kernel/gdt/gdt.c new file mode 100644 index 0000000..4886dc3 --- /dev/null +++ b/src/kernel/gdt/gdt.c @@ -0,0 +1,56 @@ +#include "gdt.h" +#include + +GDT_t *table = 0x0; +extern GDTR_t gdtr; +void get_gdtr() { + uint32_t base = 0x0000; + + *table = (GDT_t){ + // NULL + make_descriptor(0, 0, 0), + // Code segment, read + make_descriptor(base, 0x8FFFF, make_code(0, 0, 1)), + // Data segment, read write + make_descriptor(base, 0x8FFFF, make_data(0, 0, 1)), + }; + gdtr.size = sizeof(Segment_Descriptor_t) * 3 - 1; + gdtr.offset = base; +} + +uint16_t make_code(uint8_t priv, uint8_t dc, uint8_t rw) { + uint16_t access = 0; + access |= (1 << 7); + access |= (priv << 5); + access |= (0b11 << 3); + access |= (dc << 2); + access |= (rw << 1); // 10 + access <<= 8; + access |= FLAG; + return access; +} + +uint16_t make_data(uint8_t priv, uint8_t dc, uint8_t rw) { + uint16_t access = 0; + access |= (1 << 7); + access |= (priv << 5); + access |= (0b10 << 3); + access |= (dc << 2); + access |= (rw << 1); // 10 + access <<= 8; + access |= FLAG; + return access; +} + +Segment_Descriptor_t make_descriptor(uint32_t base, uint32_t limit, + uint16_t access_flag) { + uint16_t lim_low = limit; + uint16_t base_low = base; + uint8_t base_mid = (base >> 16); + uint8_t access_byte = access_flag >> 8; + uint8_t lim_flag = ((access_flag << 4) | (limit >> 16)); + uint8_t base_high = (base >> 24); + return (Segment_Descriptor_t){ + lim_low, base_low, base_mid, access_byte, lim_flag, base_high, + }; +} -- cgit v1.2.3