User mode code can now run !

We have a sample process (hardcoded in ASM in Task.wtf.asm) that
displays a's and sleeps 20ms, but it's on a hidden virtual terminal so
it's useless :D

4 files changed, 60 insertions, 1 deletions

diff --git a/Source/Kernel/MemoryManager/GDT.ns.cpp b/Source/Kernel/MemoryManager/GDT.ns.cpp
index 0bb606d..f1f5c94 100644
--- a/Source/Kernel/MemoryManager/GDT.ns.cpp
+++ b/Source/Kernel/MemoryManager/GDT.ns.cpp
@@ -1,6 +1,9 @@
 #include "GDT.ns.h"
 
 extern "C" void gdt_flush(u32int);
+extern "C" void tss_flush();
+
+using namespace CMem;	//For memset
 
 #define GDT_ENTRIES 6
 
@@ -8,6 +11,7 @@ namespace GDT {
 
 gdt_entry_t gdt_entries[GDT_ENTRIES];
 gdt_ptr_t   gdt_ptr;
+tss_entry_t tss_entry;
 
 void setGate(s32int num, u32int base, u32int limit, u8int access, u8int gran) {
 	gdt_entries[num].base_low = (base & 0xFFFF);
@@ -20,6 +24,22 @@ void setGate(s32int num, u32int base, u32int limit, u8int access, u8int gran) {
 	gdt_entries[num].access = access;
 }
 
+void writeTSS(s32int num, u16int ss0, u32int esp0) {
+	u32int base = (u32int)&tss_entry;
+	u32int limit = base + sizeof(tss_entry);
+
+	setGate(num, base, limit, 0xE9, 0x00);
+
+	memset((u8int*)&tss_entry, 0, sizeof(tss_entry_t));
+
+	tss_entry.ss0 = ss0;
+	tss_entry.esp0 = esp0;
+
+	tss_entry.cs = 0x0B;	//0x0B = Kernel code segment + RPL=3 (meaning it is supposed to be called from user mode)
+	//0x13 = Kernel data segment + RPL=3 (meaning to be called from ring3)
+	tss_entry.ss = tss_entry.ds = tss_entry.es = tss_entry.fs = tss_entry.gs = 0x13;
+}
+
 void init() {
 	gdt_ptr.limit = (sizeof(gdt_entry_t) * GDT_ENTRIES) - 1;
 	gdt_ptr.base = (u32int)&gdt_entries;
@@ -29,8 +49,10 @@ void init() {
 	setGate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);	//Kernel data segment
 	setGate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);	//User code segment
 	setGate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);	//User data segment
+	writeTSS(5, 0x10, 0x0);
 
 	gdt_flush((u32int)&gdt_ptr);
+	tss_flush();
 }
 
 }
diff --git a/Source/Kernel/MemoryManager/GDT.ns.h b/Source/Kernel/MemoryManager/GDT.ns.h
index 7a9f95f..94306a4 100644
--- a/Source/Kernel/MemoryManager/GDT.ns.h
+++ b/Source/Kernel/MemoryManager/GDT.ns.h
@@ -13,12 +13,44 @@ namespace GDT {
 		u8int base_high;
 	} __attribute__((packed));
 
+	// A struct describing a Task State Segment.
+	struct tss_entry_t {
+		u32int prev_tss;   // The previous TSS - if we used hardware task switching this would form a linked list.
+		u32int esp0;       // The stack pointer to load when we change to kernel mode.
+		u32int ss0;        // The stack segment to load when we change to kernel mode.
+		u32int esp1;       // Unused...
+		u32int ss1;
+		u32int esp2;
+		u32int ss2;
+		u32int cr3;
+		u32int eip;
+		u32int eflags;
+		u32int eax;
+		u32int ecx;
+		u32int edx;
+		u32int ebx;
+		u32int esp;
+		u32int ebp;
+		u32int esi;
+		u32int edi;
+		u32int es;         // The value to load into ES when we change to kernel mode.
+		u32int cs;         // The value to load into CS when we change to kernel mode.
+		u32int ss;         // The value to load into SS when we change to kernel mode.
+		u32int ds;         // The value to load into DS when we change to kernel mode.
+		u32int fs;         // The value to load into FS when we change to kernel mode.
+		u32int gs;         // The value to load into GS when we change to kernel mode.
+		u32int ldt;        // Unused...
+		u16int trap;
+		u16int iomap_base;
+	} __attribute__((packed));
+
 	struct gdt_ptr_t {
 		u16int limit;
 		u32int base;
 	} __attribute__((packed));
 
 	void init();
+	extern tss_entry_t tss_entry;	//Used for setting kernel stack
 }
 
 #endif
diff --git a/Source/Kernel/MemoryManager/GDT.wtf.asm b/Source/Kernel/MemoryManager/GDT.wtf.asm
index eb216ed..beb668d 100644
--- a/Source/Kernel/MemoryManager/GDT.wtf.asm
+++ b/Source/Kernel/MemoryManager/GDT.wtf.asm
@@ -15,3 +15,9 @@ gdt_flush:
 .flush:
   ret
   
+
+[GLOBAL tss_flush]
+tss_flush:
+	mov ax, 0x2B		;entry 5 = 0x28, with RPL=3
+	ltr ax
+	ret
diff --git a/Source/Kernel/MemoryManager/PhysMem.ns.cpp b/Source/Kernel/MemoryManager/PhysMem.ns.cpp
index 382e8a4..eb6fbf1 100644
--- a/Source/Kernel/MemoryManager/PhysMem.ns.cpp
+++ b/Source/Kernel/MemoryManager/PhysMem.ns.cpp
@@ -28,7 +28,6 @@ void initPaging(u32int mem_size) {
 		kernelPageDirectory->tables[i] = kernelPageDirectory->tables[768 + i];
 	}
 	DEBUG_HEX((u32int)kernelPageDirectory->physicalAddr); DEBUG(" is page dir phys addr.");
-	//asm volatile("hlt");
 
 	kernelPageDirectory->switchTo();
 	DEBUG("Paging enabled !");