arch: i386: simplifiy GDT setup

Simplify the setup and definitions of GDT/TSS entries.

Signed-off-by: Danny Holman <dholman@gymli.org>

4 files changed, 176 insertions, 68 deletions

diff --git a/arch/i386/boot/boot.s b/arch/i386/boot/boot.s
index c62abbf..4b32ca2 100644
--- a/arch/i386/boot/boot.s
+++ b/arch/i386/boot/boot.s
@@ -25,7 +25,6 @@ boot_page_table0:
 .section .multiboot.text, "a"
 .global _start
 .type _start, @function
-
 _start:
         movl $(boot_page_table0 - 0xC0000000), %edi
         movl $0, %esi
@@ -73,6 +72,7 @@ _start:
         call pic_remap
 
         call kernel_main
+        call jump_userspace
 
         cli
 1:      hlt
@@ -80,11 +80,9 @@ _start:
 
 .global flush_gdt
 .type flush_gdt, @function
-
 flush_gdt:
         cli
-        movl 4(%esp), %eax
-        lgdt (%eax)
+        lgdt (gp)
         movw $0x10, %ax
         movw %ax, %ds
         movw %ax, %es
@@ -92,4 +90,34 @@ flush_gdt:
         movw %ax, %gs
         movw %ax, %ss
         jmp $0x08, $.flush
-.flush: ret
+.flush:
+        ret
+
+.global flush_tss
+.type flush_tss, @function
+flush_tss:
+        movw $0x28, %ax
+        ltr %ax
+        ret
+
+.global jump_userspace
+.type jump_userspace, @function
+jump_userspace:
+        cli
+        movw $0x23, %ax
+        movw %ax, %ds
+        movw %ax, %es
+        movw %ax, %fs
+        movw %ax, %gs
+
+        pushl $0x23
+        pushl %esp
+        pushf
+        orl $0x200, (%esp)
+        pushl $0x8
+        pushl $test_user_function
+        iret
+
+test_user_function:
+        movl $1, %eax
+        int $0x80
diff --git a/arch/i386/boot/gdt.c b/arch/i386/boot/gdt.c
index 6552721..3972e53 100644
--- a/arch/i386/boot/gdt.c
+++ b/arch/i386/boot/gdt.c
@@ -1,80 +1,95 @@
+#include <kernel/string.h>
 #include <stdint.h>
 
-#define SEG_DESCTYPE(x)  ((x) << 0x04) // Descriptor type (0 for system, 1 for code/data)
-#define SEG_PRES(x)      ((x) << 0x07) // Present
-#define SEG_SAVL(x)      ((x) << 0x0C) // Available for system use
-#define SEG_LONG(x)      ((x) << 0x0D) // Long mode
-#define SEG_SIZE(x)      ((x) << 0x0E) // Size (0 for 16-bit, 1 for 32)
-#define SEG_GRAN(x)      ((x) << 0x0F) // Granularity (0 for 1B - 1MB, 1 for 4KB - 4GB)
-#define SEG_PRIV(x)     (((x) &  0x03) << 0x05)   // Set privilege level (0 - 3)
- 
-#define SEG_DATA_RD        0x00 // Read-Only
-#define SEG_DATA_RDA       0x01 // Read-Only, accessed
-#define SEG_DATA_RDWR      0x02 // Read/Write
-#define SEG_DATA_RDWRA     0x03 // Read/Write, accessed
-#define SEG_DATA_RDEXPD    0x04 // Read-Only, expand-down
-#define SEG_DATA_RDEXPDA   0x05 // Read-Only, expand-down, accessed
-#define SEG_DATA_RDWREXPD  0x06 // Read/Write, expand-down
-#define SEG_DATA_RDWREXPDA 0x07 // Read/Write, expand-down, accessed
-#define SEG_CODE_EX        0x08 // Execute-Only
-#define SEG_CODE_EXA       0x09 // Execute-Only, accessed
-#define SEG_CODE_EXRD      0x0A // Execute/Read
-#define SEG_CODE_EXRDA     0x0B // Execute/Read, accessed
-#define SEG_CODE_EXC       0x0C // Execute-Only, conforming
-#define SEG_CODE_EXCA      0x0D // Execute-Only, conforming, accessed
-#define SEG_CODE_EXRDC     0x0E // Execute/Read, conforming
-#define SEG_CODE_EXRDCA    0x0F // Execute/Read, conforming, accessed
- 
-#define GDT_CODE_PL0    (SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
-                         SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
-                         SEG_PRIV(0)     | SEG_CODE_EXRD)
- 
-#define GDT_DATA_PL0    (SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
-                         SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
-                         SEG_PRIV(0)     | SEG_DATA_RDWR)
- 
-#define GDT_CODE_PL3    (SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
-                         SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
-                         SEG_PRIV(3)     | SEG_CODE_EXRD)
- 
-#define GDT_DATA_PL3    (SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
-                         SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
-                         SEG_PRIV(3)     | SEG_DATA_RDWR)
+struct gdt_entry {
+        uint16_t limit_low;
+        uint16_t base_low;
+        uint8_t base_middle;
+        uint8_t access;
+        uint8_t gran;
+        uint8_t base_high;
+} __attribute__((packed));
 
-struct gpt_ptr {
+struct gdt_ptr {
         uint16_t limit;
         uint32_t base;
-}__attribute__((packed));
+} __attribute__((packed));
 
-uint64_t gdt_desc[5];
-struct gpt_ptr gp;
+struct tss_entry {
+        uint32_t link;
+        uint32_t esp0;
+        uint32_t ss0;
+        uint32_t esp1;
+        uint32_t ss2;
+        uint32_t cr3;
+        uint32_t eip;
+        uint32_t eflags;
+        uint32_t eax;
+        uint32_t ecx;
+        uint32_t edx;
+        uint32_t ebx;
+        uint32_t esp;
+        uint32_t ebp;
+        uint32_t esi;
+        uint32_t edi;
+        uint32_t es;
+        uint32_t cs;
+        uint32_t ss;
+        uint32_t ds;
+        uint32_t fs;
+        uint32_t gs;
+        uint32_t ldtr;
+        uint16_t trap;
+        uint16_t iomap_base;
+} __attribute__((packed));
 
-extern void flush_gdt(struct gpt_ptr *ptr);
+struct gdt_entry desc[6];
+struct gdt_ptr gp;
+struct tss_entry tss_entry;
 
-uint64_t create_gdt_entry(uint32_t base, uint32_t limit, uint16_t flag) {
-        uint64_t ret;
+extern void flush_gdt(void);
+extern void flush_tss(void);
 
-        ret =   limit           & 0x000F0000;
-        ret |=  (flag << 8)     & 0x00F0FF00;
-        ret |=  (base >> 16)    & 0x000000FF;
-        ret |=  base            & 0xFF000000;
+void gdt_set_gate(int num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran) {
+        desc[num].base_low = (base & 0xFFFF);
+        desc[num].base_middle = (base >> 16) & 0xFF;
+        desc[num].base_high = (base >> 24) & 0xFF;
 
-        ret <<= 32;
+        desc[num].limit_low = (limit & 0xFFFF);
+        desc[num].gran = (limit >> 16) & 0x0F;
+        desc[num].gran |= (gran & 0xF0);
+        desc[num].access = access;
+}
 
-        ret |= base     << 16;
-        ret |= limit    & 0x0000FFFF;
+void write_tss(int num, uint16_t ss0, uint16_t esp0) {
+        uint32_t base = (uint32_t)&tss_entry;
+        uint32_t limit = base + sizeof(tss_entry);
 
-        return ret;
+        gdt_set_gate(num, base, limit, 0xE9, 0x00);
+        memset(&tss_entry, 0x0, sizeof(tss_entry));
+        
+        tss_entry.ss0 = ss0;
+        tss_entry.esp0 = esp0;
+        tss_entry.cs = 0x0B;
+        tss_entry.ss = 0x13;
+        tss_entry.ds = 0x13;
+        tss_entry.es = 0x13;
+        tss_entry.fs = 0x13;
+        tss_entry.gs = 0x13;
+        tss_entry.iomap_base = sizeof(tss_entry);
 }
 
 void gdt_install(void) {
-        gp.limit = 64 * 5 - 1;
-        gp.base = (uint32_t)&gdt_desc;
+        gp.limit = (sizeof(struct gdt_entry) * 6) - 1;
+        gp.base = (uint32_t)&desc;
+
+        gdt_set_gate(0, 0, 0, 0, 0);
+        gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
+        gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
+        gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
+        gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
+        write_tss(5, 0x10, 0x0);
 
-        gdt_desc[0] = create_gdt_entry(0, 0, 0);
-        gdt_desc[1] = create_gdt_entry(0, 0x000FFFFF, GDT_CODE_PL0);
-        gdt_desc[2] = create_gdt_entry(0, 0x000FFFFF, GDT_DATA_PL0);
-        gdt_desc[3] = create_gdt_entry(0, 0x000FFFFF, GDT_DATA_PL3);
-        gdt_desc[4] = create_gdt_entry(0, 0x000FFFFF, GDT_DATA_PL3);
-        flush_gdt(&gp);
+        flush_gdt();
+        flush_tss();
 }
diff --git a/arch/i386/boot/tss.c b/arch/i386/boot/tss.c
new file mode 100644
index 0000000..2edfa76
--- /dev/null
+++ b/arch/i386/boot/tss.c
@@ -0,0 +1,26 @@
+#include "tss.h"
+#include <kernel/string.h>
+
+struct tss tss_entry;
+
+uint64_t create_tss_entry(uint16_t ss0, uint32_t esp0) {
+        uint32_t base = (uint32_t)&tss_entry;
+        uint32_t limit = base + sizeof(&tss_entry);
+        uint64_t ret = create_gdt_entry(base, limit, 0xE9);
+
+        memset(&tss_entry, 0, sizeof(struct tss));
+        tss_entry.ss0 = ss0;
+        tss_entry.esp0 = esp0;
+        tss_entry.cs = 0x08;
+        tss_entry.ss = 0x13;
+        tss_entry.ds = 0x13;
+        tss_entry.es = 0x13;
+        tss_entry.fs = 0x13;
+        tss_entry.gs = 0x13;
+        tss_entry.io_offset = sizeof(struct tss) & 0xFFFF;
+        return ret;
+}
+
+void set_kernel_stack(uint32_t stack) {
+        tss_entry.esp0 = stack;
+}
diff --git a/arch/i386/boot/tss.h b/arch/i386/boot/tss.h
new file mode 100644
index 0000000..28bae6e
--- /dev/null
+++ b/arch/i386/boot/tss.h
@@ -0,0 +1,39 @@
+#ifndef I386_TSS_H
+#define I386_TSS_H
+
+#include <stdint.h>
+
+struct tss {
+        uint32_t link;
+        uint32_t esp0;
+        uint32_t ss0;
+        uint32_t esp1;
+        uint32_t ss2;
+        uint32_t cr3;
+        uint32_t eip;
+        uint32_t eflags;
+        uint32_t eax;
+        uint32_t ecx;
+        uint32_t edx;
+        uint32_t ebx;
+        uint32_t esp;
+        uint32_t ebp;
+        uint32_t esi;
+        uint32_t edi;
+        uint32_t es;
+        uint32_t cs;
+        uint32_t ss;
+        uint32_t ds;
+        uint32_t fs;
+        uint32_t gs;
+        uint32_t ldtr;
+        uint32_t io_offset;
+}__attribute__((packed));
+
+void flush_tss(void);
+
+uint64_t create_gdt_entry(uint32_t base, uint32_t limit, uint16_t flag);
+uint64_t create_tss_entry(uint16_t ss0, uint32_t esp0);
+void set_kernel_stack(uint32_t stack);
+
+#endif