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Completely overhauled how GDT is defined to make it much easier to add more entries to the GDT in the future

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This commit is contained in:
Xnoe 2021-11-21 16:39:31 +00:00
parent 760069bbb9
commit f581e6b6fe
Signed by: xnoe
GPG Key ID: 45AC398F44F0DAFE
2 changed files with 128 additions and 55 deletions
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138
src/kernel/gdt.cpp
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@ -1,57 +1,89 @@
#include "gdt.h"
constexpr tss_struct::tss_struct() :
link(0),
_reserved0(0),
esp0(0),
ss0(0),
_reserved1(0),
esp1(0),
ss1(0),
_reserved2(0),
esp2(0),
ss2(0),
_reserved3(0),
cr3(0),
eip(0),
eflags(0),
eax(0),
ebx(0),
ecx(0),
edx(0),
esp(0),
ebp(0),
esi(0),
edi(0),
es(0),
_reserved4(0),
cs(0),
_reserved5(0),
ss(0),
_reserved6(0),
ds(0),
_reserved7(0),
fs(0),
_reserved8(0),
gs(0),
_reserved9(0),
ldtr(0),
_reserved10(0),
_reserved11(0),
iopb(0)
{}
tss_struct tss = tss_struct();
constexpr gdt_entry::gdt_entry(uint32_t limit, uint32_t base, bool rw, bool exec, bool system, uint8_t ring) :
limit_lo(limit & 0xffff),
limit_hi((limit & 0xf0000) >> 16),
base_lo(base & 0xffff),
base_mid((base & 0xff0000) >> 16),
base_hi((base & 0xff000000) >> 24),
__ignored__(0),
accessed(0),
granularity(1),
size(1),
present(1),
read_write(rw),
executable(exec),
system_segment(system),
privilege(ring),
direction(0)
{}
constexpr gdt_entry::gdt_entry() :
limit_lo(0),
base_lo(0),
base_mid(0),
accessed(0),
read_write(0),
direction(0),
executable(0),
system_segment(0),
privilege(0),
present(0),
limit_hi(0),
__ignored__(0),
size(0),
granularity(0),
base_hi(0)
{}
gdt_entry gdt[] = {
(gdt_entry){ // Null Segment
.limit_lo = 0,
.base_lo = 0,
.base_mid = 0,
.accessed = 0,
.read_write = 0,
.direction = 0,
.executable = 0,
.system_segment = 0,
.privilege = 0,
.present = 0,
.limit_hi = 0,
.__ignored__ = 0,
.size = 0,
.granularity = 0,
.base_hi = 0,
},
(gdt_entry){ // Code Segment
.limit_lo = 0xffff,
.base_lo = 0,
.base_mid = 0,
.accessed = 0,
.read_write = 1,
.direction = 0,
.executable = 1,
.system_segment = 1,
.privilege = 0,
.present = 1,
.limit_hi = 0xf,
.__ignored__ = 0,
.size = 1,
.granularity = 1,
.base_hi = 0
},
(gdt_entry){ // Data Segment
.limit_lo = 0xffff,
.base_lo = 0,
.base_mid = 0,
.accessed = 0,
.read_write = 1,
.direction = 0,
.executable = 0,
.system_segment = 1,
.privilege = 0,
.present = 1,
.limit_hi = 0xf,
.__ignored__ = 0,
.size = 1,
.granularity = 1,
.base_hi = 0
}
gdt_entry(), // Null Segment
gdt_entry(0xfffff, 0, 1, 1, 1, 0), // Code Segment
gdt_entry(0xfffff, 0, 1, 0, 1, 0), // Data Segment
gdt_entry(sizeof(tss), &tss, 0, 1, 0, 0) // Task State Segment 1
};
gdt_descr descr = (gdt_descr){
@ -59,14 +91,10 @@ gdt_descr descr = (gdt_descr){
.offset = gdt,
};
__attribute__((far)) void far_call() {}
void init_gdt() {
asm volatile("lgdt %0;"
"mov $0x10, %%eax;"
"mov %%eax, %%ss;"
"mov $0x10, %%eax;"
"mov %%eax, %%ds" : : "m" (descr));
far_call();
}

45
src/kernel/gdt.h
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@ -3,6 +3,48 @@
#include "types.h"
struct __attribute__((packed)) tss_struct {
uint16_t link;
uint16_t _reserved0;
uint32_t esp0;
uint16_t ss0;
uint16_t _reserved1;
uint32_t esp1;
uint16_t ss1;
uint16_t _reserved2;
uint32_t esp2;
uint16_t ss2;
uint16_t _reserved3;
uint32_t cr3;
uint32_t eip;
uint32_t eflags;
uint32_t eax;
uint32_t ebx;
uint32_t ecx;
uint32_t edx;
uint32_t esp;
uint32_t ebp;
uint32_t esi;
uint32_t edi;
uint16_t es;
uint16_t _reserved4;
uint16_t cs;
uint16_t _reserved5;
uint16_t ss;
uint16_t _reserved6;
uint16_t ds;
uint16_t _reserved7;
uint16_t fs;
uint16_t _reserved8;
uint16_t gs;
uint16_t _reserved9;
uint16_t ldtr;
uint16_t _reserved10;
uint16_t _reserved11;
uint16_t iopb;
constexpr tss_struct();
};
struct __attribute__((packed)) gdt_entry {
uint32_t limit_lo : 16;
uint32_t base_lo : 16;
@ -22,6 +64,9 @@ struct __attribute__((packed)) gdt_entry {
uint32_t granularity : 1;
uint32_t base_hi : 8;
constexpr gdt_entry(uint32_t limit, uint32_t base, bool rw, bool exec, bool system, uint8_t ring);
constexpr gdt_entry();
};
struct __attribute__((packed)) gdt_descr {