From 5f3cbb988dc3b9ead7165f3d77c41248e76f80b4 Mon Sep 17 00:00:00 2001
From: Alexander Myltsev <a.myltsev@gmail.com>
Date: Wed, 14 Dec 2022 12:28:30 +0300
Subject: [PATCH] Fix TSS init.

---
 cpu/gdt.c | 64 +++++++++++--------------------------------------------
 cpu/gdt.h | 44 ++++++++++++++++++++++++++++++++++++++
 proc.c    | 13 ++++++++---
 3 files changed, 67 insertions(+), 54 deletions(-)

diff --git a/cpu/gdt.c b/cpu/gdt.c
index f5b2572..f2356a3 100644
--- a/cpu/gdt.c
+++ b/cpu/gdt.c
@@ -1,4 +1,5 @@
 #include "gdt.h"
+#include "../lib/string.h"
 
 #include <stdint.h>
 
@@ -18,8 +19,6 @@ struct seg_desc_t {
     uint8_t base_31_24;     // High bits of segment base address
 } __attribute__((packed));
 
-typedef unsigned uint;
-
 #define SEG(type, base, lim, dpl) (struct seg_desc_t)    \
 { ((lim) >> 12) & 0xffff, (uint)(base) & 0xffff,      \
   ((uint)(base) >> 16) & 0xff, type, 1, dpl, 1,       \
@@ -38,66 +37,29 @@ void init_seg_desc() {
     seg_desc[SEG_UDATA] = SEG(STA_W,       USER_BASE, 0xffffffff - USER_BASE, DPL_USER);
 }
 
-typedef uint16_t ushort;
-
-struct taskstate {
-    uint link;         // Old ts selector
-    uint esp0;         // Stack pointers and segment selectors
-    ushort ss0;        //   after an increase in privilege level
-    ushort padding1;
-    uint *esp1;
-    ushort ss1;
-    ushort padding2;
-    uint *esp2;
-    ushort ss2;
-    ushort padding3;
-    void *cr3;         // Page directory base
-    uint *eip;         // Saved state from last task switch
-    uint eflags;
-    uint eax;          // More saved state (registers)
-    uint ecx;
-    uint edx;
-    uint ebx;
-    uint *esp;
-    uint *ebp;
-    uint esi;
-    uint edi;
-    ushort es;         // Even more saved state (segment selectors)
-    ushort padding4;
-    ushort cs;
-    ushort padding5;
-    ushort ss;
-    ushort padding6;
-    ushort ds;
-    ushort padding7;
-    ushort fs;
-    ushort padding8;
-    ushort gs;
-    ushort padding9;
-    ushort ldt;
-    ushort padding10;
-    ushort t;          // Trap on task switch
-    ushort iomb;       // I/O map base address
-} tss;
-
 struct gdt_desc_t {
     uint16_t size;
     void* ptr;
 } __attribute__((packed));
 
 void load_gdt() {
-    seg_desc[SEG_TSS] = SEG16(STS_T32A, &tss, sizeof(tss)-1, 0);
-    seg_desc[SEG_TSS].s = 0;
-    tss.ss0 = SEG_KDATA << 3;
-    tss.esp0 = KERN_STACK_BASE;
-    // setting IOPL=0 in eflags *and* iomb beyond the tss segment limit
-    // forbids I/O instructions (e.g., inb and outb) from user space
-    tss.iomb = (ushort) 0xFFFF;
     init_seg_desc();
 
     struct gdt_desc_t gdt_desc;
     gdt_desc.size = sizeof(seg_desc) - 1;
     gdt_desc.ptr = seg_desc;
     asm("lgdt %0": : "m"(gdt_desc));
+}
+
+void switchuvm(struct taskstate *tss, void* esp) {
+    memset(tss, 0, sizeof(*tss));
+    seg_desc[SEG_TSS] = SEG16(STS_T32A, tss, sizeof(*tss)-1, 0);
+    seg_desc[SEG_TSS].s = 0;
+    tss->ss0 = SEG_KDATA << 3;
+    tss->esp0 = (uint)esp;
+    // setting IOPL=0 in eflags *and* iomb beyond the tss segment limit
+    // forbids I/O instructions (e.g., inb and outb) from user space
+    tss->iomb = (ushort) 0xFFFF;
+
     asm("ltr %0": : "r"((ushort)(SEG_TSS << 3)));
 }
diff --git a/cpu/gdt.h b/cpu/gdt.h
index 0f174b8..00dd40b 100644
--- a/cpu/gdt.h
+++ b/cpu/gdt.h
@@ -29,5 +29,49 @@
 #define KERN_STACK_BASE  0x90000
 
 #ifndef __ASSEMBLER__
+typedef unsigned uint;
+typedef unsigned short ushort;
+
+struct taskstate {
+    uint link;         // Old ts selector
+    uint esp0;         // Stack pointers and segment selectors
+    ushort ss0;        //   after an increase in privilege level
+    ushort padding1;
+    uint *esp1;
+    ushort ss1;
+    ushort padding2;
+    uint *esp2;
+    ushort ss2;
+    ushort padding3;
+    void *cr3;         // Page directory base
+    uint *eip;         // Saved state from last task switch
+    uint eflags;
+    uint eax;          // More saved state (registers)
+    uint ecx;
+    uint edx;
+    uint ebx;
+    uint *esp;
+    uint *ebp;
+    uint esi;
+    uint edi;
+    ushort es;         // Even more saved state (segment selectors)
+    ushort padding4;
+    ushort cs;
+    ushort padding5;
+    ushort ss;
+    ushort padding6;
+    ushort ds;
+    ushort padding7;
+    ushort fs;
+    ushort padding8;
+    ushort gs;
+    ushort padding9;
+    ushort ldt;
+    ushort padding10;
+    ushort t;          // Trap on task switch
+    ushort iomb;       // I/O map base address
+};
+
 void load_gdt();
+void switchuvm(struct taskstate *tss, void* esp);
 #endif
diff --git a/proc.c b/proc.c
index 3c19495..6b19510 100644
--- a/proc.c
+++ b/proc.c
@@ -17,12 +17,18 @@ struct kstack {
     uint32_t space[400];
     struct context context;
     registers_t trapframe;
+    char bottom[];
+};
+
+struct task {
+    struct taskstate tss;
+    struct kstack stack;
 };
 
 struct vm {
     void *kernel_thread;
     void *user_thread;
-    struct kstack *user_kstack;
+    struct task *user_task;
 } *vm;
 
 void trapret();
@@ -31,7 +37,8 @@ void swtch(void** oldstack, void* newstack);
 void run_elf(const char* name) {
     if (!vm) {
         vm = kmalloc(sizeof(struct vm));
-        vm->user_kstack = kmalloc(sizeof(struct kstack));
+        vm->user_task = kmalloc(sizeof(struct task));
+        switchuvm(&vm->user_task->tss, vm->user_task->stack.bottom);
     }
     if (read_file(name, (void*)USER_BASE, 100 << 20) <= 0) {
         printk(name);
@@ -40,7 +47,7 @@ void run_elf(const char* name) {
     }
     Elf32_Ehdr *hdr = (void*)USER_BASE;
 
-    struct kstack *u = vm->user_kstack;
+    struct kstack *u = &vm->user_task->stack;
     memset(u, 0, sizeof(*u));
     u->context.eip = (uint32_t)trapret;