Implemented basic syscalls and user mode

Doesn't completely work right now

11 files changed, 233 insertions, 34 deletions

diff --git a/src/kernel/boot.asm b/src/kernel/boot.asm
index fad05ff..8f24066 100644
--- a/src/kernel/boot.asm
+++ b/src/kernel/boot.asm
@@ -50,6 +50,25 @@ stublet:
 
 %include "src/kernel/interact.asm"
 
+global switch_to_user
+switch_to_user:
+     cli
+     mov ax,0x23
+     mov ds,ax
+     mov es,ax
+     mov fs,ax
+     mov gs,ax
+
+     mov eax,esp
+     push 0x23
+     push eax
+     pushf
+     pop eax
+     or eax, 0x200
+     push eax
+     push 0x1B
+     iret
+
 ; Store the stack
 SECTION .bss
     resb 0x2000 ; Reserve 8KiB
diff --git a/src/kernel/fs/initrd.c b/src/kernel/fs/initrd.c
index 906498e..acaceb8 100644
--- a/src/kernel/fs/initrd.c
+++ b/src/kernel/fs/initrd.c
@@ -4,6 +4,7 @@
 #include <kernel/lib/lib.h>
 #include <kernel/lib/alloc.h>
 #include <kernel/io/io.h>
+#include <kernel/graphics/vesa.h>
 
 initrd_header_t *initrd_header;
 initrd_file_header_t *file_headers;
@@ -103,3 +104,28 @@ fs_node_t *initialise_initrd(uint32_t location) {
     }
     return initrd_root;
 }
+
+void initrd_test() {
+    int i = 0;
+    struct dirent *node = 0;
+    vesa_draw_string("\n");
+    while ((node = readdir_fs(fs_root, i)) != 0) {
+        vesa_draw_string("Found file: ");
+        vesa_draw_string(node->name);
+        vesa_draw_string("\n");
+        fs_node_t *fsnode = finddir_fs(fs_root, node->name);
+
+        if ((fsnode->flags & 0x7) == FS_DIRECTORY)
+            vesa_draw_string("\t (directory)\n");
+        else {
+            vesa_draw_string("\t contents: \"");
+            uint8_t buf[fsnode->length];
+            uint32_t sz = read_fs(fsnode, 0, fsnode->length, buf);
+            for (uint32_t j = 0; j < sz; j++)
+                vesa_draw_char(buf[j]);
+
+            vesa_draw_string("\"\n");
+        }
+        i++;
+    }
+}
\ No newline at end of file
diff --git a/src/kernel/fs/initrd.h b/src/kernel/fs/initrd.h
index 10dec22..bb5c376 100644
--- a/src/kernel/fs/initrd.h
+++ b/src/kernel/fs/initrd.h
@@ -17,4 +17,6 @@ typedef struct {
 
 fs_node_t *initialise_initrd(uint32_t location);
 
+void initrd_test();
+
 #endif
diff --git a/src/kernel/gdt/gdt.asm b/src/kernel/gdt/gdt.asm
index c2128e4..6cb2b7d 100644
--- a/src/kernel/gdt/gdt.asm
+++ b/src/kernel/gdt/gdt.asm
@@ -11,4 +11,10 @@ gdt_flush:
     mov ss, ax
     jmp 0x08:flush2 ; Code segment offset
 flush2:
-    ret ; Returns to C code
\ No newline at end of file
+    ret ; Returns to C code
+
+global tss_flush
+tss_flush:
+    mov ax, 0x2B
+    ltr ax
+    ret
\ No newline at end of file
diff --git a/src/kernel/gdt/gdt.c b/src/kernel/gdt/gdt.c
index a4d6a57..b933950 100644
--- a/src/kernel/gdt/gdt.c
+++ b/src/kernel/gdt/gdt.c
@@ -1,4 +1,8 @@
+#include <stdint.h>
+#include <kernel/gdt/gdt.h>
 #include <kernel/system.h>
+#include <kernel/lib/lib.h>
+#include <kernel/io/io.h>
 
 struct gdt_entry {
     unsigned short limit_low;
@@ -14,12 +18,46 @@ struct gdt_ptr {
     void *base;
 } __attribute__((packed));
 
-struct gdt_entry gdt[3];
+struct gdt_entry gdt[6];
 struct gdt_ptr gp;
 
+struct tss_entry_struct {
+    uint32_t prev_tss;
+    uint32_t esp0;
+    uint32_t ss0;
+    uint32_t esp1;
+    uint32_t ss1;
+    uint32_t esp2;
+    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 ldt;
+    uint16_t trap;
+    uint16_t iomap_base;
+} __attribute__((packed));
+
+struct tss_entry_struct tss_entry;
+
 extern void gdt_flush();
 
-void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned char access, unsigned char gran) {
+extern void tss_flush();
+
+void gdt_set_gate(int32_t num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran) {
     // Set descriptor base address
     gdt[num].base_low = (base & 0xFFFF);
     gdt[num].base_middle = (base >> 16) & 0xFF;
@@ -36,7 +74,7 @@ void gdt_set_gate(int num, unsigned long base, unsigned long limit, unsigned cha
 
 void gdt_install() {
     // Set GDT pointer and limit
-    gp.limit = (sizeof(struct gdt_entry) * 3) - 1;
+    gp.limit = (sizeof(struct gdt_entry) * 6) - 1;
     gp.base = &gdt;
 
     // NULL descriptor
@@ -48,8 +86,37 @@ void gdt_install() {
     // Data segment
     gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
 
+    // User mode code segment
+    gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
+
+    // User mode data segment
+    gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
+
+    // Write TSS
+    tss_write(5, 0x10, 0x0);
+
     // Remove old GDT and install the new changes!
     gdt_flush();
+    tss_flush(); // FAILS
 
     vga_log("Installed Global Descriptor Table", 2);
-}
\ No newline at end of file
+}
+
+void tss_write(int32_t num, uint16_t ss0, uint32_t esp0) {
+    uint32_t base = (uint32_t) &tss_entry;
+    uint32_t limit = base + sizeof(tss_entry);
+
+    gdt_set_gate(num, base, limit, 0xE9, 0x00);
+
+    memset(&tss_entry, 0, sizeof(tss_entry));
+
+    tss_entry.ss0 = ss0;
+    tss_entry.esp0 = esp0;
+
+    tss_entry.cs = 0x0b;
+    tss_entry.ss = tss_entry.ds = tss_entry.es = tss_entry.fs = tss_entry.gs = 0x13;
+}
+
+void set_kernel_stack(uint32_t stack) {
+    tss_entry.esp0 = stack;
+}
diff --git a/src/kernel/gdt/gdt.h b/src/kernel/gdt/gdt.h
index de8a6ff..0fffc20 100644
--- a/src/kernel/gdt/gdt.h
+++ b/src/kernel/gdt/gdt.h
@@ -6,4 +6,6 @@
  */
 void gdt_install();
 
+void tss_write(int32_t num, uint16_t ss0, uint32_t esp0);
+
 #endif
diff --git a/src/kernel/graphics/vesa.c b/src/kernel/graphics/vesa.c
index 3f8a9ba..32ca717 100644
--- a/src/kernel/graphics/vesa.c
+++ b/src/kernel/graphics/vesa.c
@@ -324,7 +324,7 @@ void vesa_keyboard_char(char ch) {
                         terminal_color);
 }
 
-void vesa_draw_string(char *data) {
+void vesa_draw_string(const char *data) {
     int i = 0;
     while (data[i] != '\0') {
         vesa_draw_char(data[i]);
diff --git a/src/kernel/graphics/vesa.h b/src/kernel/graphics/vesa.h
index 748f8d0..3fcef24 100644
--- a/src/kernel/graphics/vesa.h
+++ b/src/kernel/graphics/vesa.h
@@ -128,6 +128,10 @@ void vesa_clear();
  */
 void vesa_set_font(int height);
 
+/**
+ * Draws a single char
+ * @param ch The char
+ */
 void vesa_draw_char(char ch);
 
 /**
@@ -140,7 +144,7 @@ void vesa_keyboard_char(char ch);
  * Draw a string in VESA mode
  * @param data The string
  */
-void vesa_draw_string(char *data);
+void vesa_draw_string(const char *data);
 
 /**
  * Draw a number in VESA mode
diff --git a/src/kernel/kernel.c b/src/kernel/kernel.c
index dd49949..dd15409 100644
--- a/src/kernel/kernel.c
+++ b/src/kernel/kernel.c
@@ -8,8 +8,11 @@
 #include <kernel/acpi/acpi.h>
 #include <kernel/mutliboot.h>
 #include <kernel/fs/initrd.h>
+#include <kernel/syscall/syscall.h>
 
-void init() {
+extern void switch_to_user();
+
+void kernel_main(struct multiboot *mboot_ptr) {
     vga_log("Installing basic features of Melvix...", 0);
     // Install features
     timer_install();
@@ -21,44 +24,25 @@ void init() {
     isrs_install();
     irq_install();
     set_optimal_resolution();
+
     // Install drivers
     asm volatile ("cli");
     keyboard_install();
     asm volatile ("sti");
-}
-
-void kernel_main(struct multiboot *mboot_ptr) {
-    init();
 
+    // Setup initial ramdisk
     assert(mboot_ptr->mods_count > 0);
     uint32_t initrd_location = *((uint32_t *) mboot_ptr->mods_addr);
     uint32_t initrd_end = *(uint32_t *) (mboot_ptr->mods_addr + 4);
     paging_set_used(0, (initrd_end >> 12) + 1);
-
     fs_root = initialise_initrd(initrd_location);
+    initrd_test();
 
-    int i = 0;
-    struct dirent *node = 0;
-    vesa_draw_string("\n");
-    while ((node = readdir_fs(fs_root, i)) != 0) {
-        vesa_draw_string("Found file: ");
-        vesa_draw_string(node->name);
-        vesa_draw_string("\n");
-        fs_node_t *fsnode = finddir_fs(fs_root, node->name);
-
-        if ((fsnode->flags & 0x7) == FS_DIRECTORY)
-            vesa_draw_string("\t (directory)\n");
-        else {
-            vesa_draw_string("\t contents: \"");
-            uint8_t buf[fsnode->length];
-            uint32_t sz = read_fs(fsnode, 0, fsnode->length, buf);
-            for (uint32_t j = 0; j < sz; j++)
-                vesa_draw_char(buf[j]);
+    // User mode!
+    syscalls_install();
+    switch_to_user();
 
-            vesa_draw_string("\"\n");
-        }
-        i++;
-    }
+    syscall_serial_write("Hello, user world!\n");
 
     // asm volatile  ("div %0" :: "r"(0)); // Exception testing x/0
     loop:
diff --git a/src/kernel/syscall/syscall.c b/src/kernel/syscall/syscall.c
new file mode 100644
index 0000000..d1dbd6b
--- /dev/null
+++ b/src/kernel/syscall/syscall.c
@@ -0,0 +1,45 @@
+#include <stdint.h>
+#include <kernel/syscall/syscall.h>
+#include <kernel/interrupts/interrupts.h>
+#include <kernel/graphics/vesa.h>
+#include <kernel/io/io.h>
+
+DEFN_SYSCALL1(vesa_draw_string, 0, const char *);
+
+DEFN_SYSCALL1(vesa_draw_number, 1, int);
+
+DEFN_SYSCALL1(serial_write, 2, const char *);
+
+static void *syscalls[3] = {
+        &vesa_draw_string,
+        &vesa_draw_number,
+        &serial_write,
+};
+uint32_t num_syscalls = 3;
+
+void syscall_handler(struct regs *r) {
+    if (r->eax >= num_syscalls)
+        return;
+
+    void *location = syscalls[r->eax];
+
+    int ret;
+    asm volatile (" \
+     push %1; \
+     push %2; \
+     push %3; \
+     push %4; \
+     push %5; \
+     call *%6; \
+     pop %%ebx; \
+     pop %%ebx; \
+     pop %%ebx; \
+     pop %%ebx; \
+     pop %%ebx; \
+   " : "=a" (ret) : "r" (r->edi), "r" (r->esi), "r" (r->edx), "r" (r->ecx), "r" (r->ebx), "r" (location));
+    r->eax = ret;
+}
+
+void syscalls_install() {
+    irq_install_handler(0x80, &syscall_handler);
+}
diff --git a/src/kernel/syscall/syscall.h b/src/kernel/syscall/syscall.h
new file mode 100644
index 0000000..d35c4e6
--- /dev/null
+++ b/src/kernel/syscall/syscall.h
@@ -0,0 +1,44 @@
+#ifndef MELVIX_SYSCALL_H
+#define MELVIX_SYSCALL_H
+
+#include <kernel/interrupts/interrupts.h>
+
+void syscalls_install();
+
+void syscall_handler(struct regs *r);
+
+#define DECL_SYSCALL0(fn) int syscall_##fn();
+#define DECL_SYSCALL1(fn, p1) int syscall_##fn(p1);
+#define DECL_SYSCALL2(fn, p1, p2) int syscall_##fn(p1,p2);
+#define DECL_SYSCALL3(fn, p1, p2, p3) int syscall_##fn(p1,p2,p3);
+#define DECL_SYSCALL4(fn, p1, p2, p3, p4) int syscall_##fn(p1,p2,p3,p4);
+#define DECL_SYSCALL5(fn, p1, p2, p3, p4, p5) int syscall_##fn(p1,p2,p3,p4,p5);
+
+#define DEFN_SYSCALL0(fn, num) \
+int syscall_##fn() { \
+ int a; \
+ asm volatile("int $0x80" : "=a" (a) : "0" (num)); \
+ return a; \
+}
+
+#define DEFN_SYSCALL1(fn, num, P1) \
+int syscall_##fn(P1 p1) { \
+ int a; \
+ asm volatile("int $0x80" : "=a" (a) : "0" (num), "b" ((int)p1)); \
+ return a; \
+}
+
+#define DEFN_SYSCALL2(fn, num, P1, P2) \
+int syscall_##fn(P1 p1, P2 p2) { \
+ int a; \
+ asm volatile("int $0x80" : "=a" (a) : "0" (num), "b" ((int)p1), "c" ((int)p2)); \
+ return a; \
+}
+
+DECL_SYSCALL1(vesa_draw_string, const char *)
+
+DECL_SYSCALL1(vesa_draw_number, int)
+
+DECL_SYSCALL1(serial_write, const char *)
+
+#endif