Usermode now loads at 0x800000, Virtual 8086 loads consistent DS&ES for data access

entry.nasm

@@ -16,7 +16,7 @@ mov es, ax
 mov ss, ax
 mov fs, ax
 mov gs, ax
-mov ebp, 0x400000
+mov ebp, 0x800000
 mov esp, ebp
 mov eax, 0x1f001f00
 mov ecx, (80*25)/2

fault.nasm

@@ -83,6 +83,7 @@ je .int30
 cmp eax, 0x21CD ; int 0x21
 je .int21
 jmp gpf_unhandled
+
 .int21:
 pop eax ; command
 cmp al, 0x00 ; get key
@@ -94,7 +95,13 @@ jne .s86
 call get_scancode
 jmp .return_to_offender
 .s86: cmp al, 0x86 ; v86 interrupt call
+je .v86int
+cmp ax, 0x86D8 ; get v86 data pointer
 jne .return_to_offender
+mov eax, 0x30000 ; V86 Data
+jmp .return_to_offender
+
+.v86int:
 add esp, 4
 add dword [esp+0], 2
 ; add a new task
@@ -120,6 +127,7 @@ push eax ; cs
 push 0xFF00 ; sp
 push 0x8000 ; ss
 jmp _enter_v86_internal_no_task ; NOT a function call
+
 .int30:
 pop eax ; return value
 jmp return_prev_task

kernel.c

@@ -171,10 +171,11 @@ Real Mode Accessible (First MB)
  01000 -  04000 Free (12kB)
  04000 -  07C00 V86 Code (15kB)
  07C00 -  08000 Boot & V86 Code (512B)
- 08000 -  20000 V86 Code (96kB)
+ 08000 -  20000 Free (96kB)
  20000 -  30000 Disk Buffer (64kB)
- 30000 -  80000 Free (320kB)
- 80000 -  90000 Real Mode Stack (64kB)
+ 30000 -  40000 V86 Data (64kB)
+ 40000 -  80000 Free (256kB)
+ 80000 -  90000 V86 Stack (64kB)
  90000 -  A0000 Free (64kB)
  A0000 -  C0000 VGA (128kB)
  C0000 -  FFFFF BIOS Area (256kB)
@@ -434,6 +435,8 @@ void SystemRun(uint8_t sysPartition) {
     RestoreVGA();
     DrawScreen((uint16_t*)0xb8000);
 
+    InitDisk();
+
     // Check for FAT partition
     {
         // TODO Check partitions beyond 0
@@ -528,7 +531,6 @@ void start() {
     setup_tss();
     init_paging();
     backup_ivtbios();
-    InitDisk();
 
     // DL contained disk number, DH contained active partition
     uint8_t SystemPartition = boot_dx >> 8;

link.ld

@@ -3,7 +3,8 @@ ENTRY(entry)
 
 SECTIONS {
     . = 0x100000;
-    _USERMODE = 0x400000;
+    _USERMODE = 0x800000;
+    _USERMODE_END = 0x1000000;
 
     .text : {
         *(.text);

paging.c

@@ -1,8 +1,7 @@
 #include "paging.h"
 
 uint32_t page_directory[1024] __attribute__((aligned(4096)));
-uint32_t first_page_table[1024] __attribute__((aligned(4096))); // 0x00000000 - 0x00400000
-uint32_t second_page_table[1024] __attribute__((aligned(4096))); // 0x00400000 - 0x00800000
+uint32_t page_tables[4][1024] __attribute__((aligned(4096)));
 
 void enable_paging() {
     asm(
@@ -13,38 +12,52 @@ void enable_paging() {
     ::"a"(page_directory));
 }
 
+// TODO Add a function which can dynamically add and remove pages,
+// that keeps track internally of what's already used?
+
+// NOTE This function cannot cross 4MB (1024 page) boundaries
+void map_pages(uintptr_t page, uintptr_t num_pages, uintptr_t phy_address, char access_flags) {
+    uintptr_t access = access_flags & 0x7;
+
+    // Each page is 4K, Each page table is 4M
+    uintptr_t page_dir_entry = page >> 10;
+    if (page_dir_entry >= 4) return;
+    uintptr_t page_index = page & 0x3ff;
+    if (page_index + num_pages > 1024) return;
+
+    // Address must be 4K aligned
+    if (phy_address & 0x3ff) return;
+
+    for (int i = 0; i < num_pages; i++)
+        page_tables[page_dir_entry][page_index + i] = phy_address + (i * 0x1000) | access_flags;
+}
+
+// User, R/W, Present
+#define USERACCESS (4|2|1)
+// Supervisor, R/W, Present
+#define SUPERACCESS (2|1)
+
 void init_paging() {
     for (int i = 0; i < 1024; i++)
         // Supervisor, R/W, Not Present
         page_directory[i] = 2;
 
-    // First Page Table
+    // 1024 Pages = 1MB
     // First MB: Real Mode
-    {
-        int i;
-        // Up to 0xC0000
-        // TODO make some areas here Read Only
-        for (i = 0;i < 16*0xC; i++)
-            // User, R/W, Present
-            first_page_table[i] = (i * 0x1000) |4|2|1;
-        // Remainder of first MB BIOS Area (writable?)
-        for (;i < 256; i++)
-            // User, R/W, Present
-            first_page_table[i] = (i * 0x1000) |4|2|1;
-    }
+    // TODO Make some of this not accessible to usermode?
+    map_pages(0x00000000 >> 12, 256, 0x00000000, USERACCESS);
     // Next 3MB: Kernel
-    for (int i = 256; i < 1024; i++)
-        // Supervisor, R/W, Present
-        first_page_table[i] = (i * 0x1000) |2|1;
+    map_pages(0x00100000 >> 12, 768, 0x00100000, SUPERACCESS);
+    // Next 4MB: Kernel
+    map_pages(0x00400000 >> 12, 1024, 0x00400000, SUPERACCESS);
 
-    // Usermode Page Table
-    for (int i = 0; i < 1024; i++)
-        // User, R/W, Present
-        second_page_table[i] = (i * 0x1000 + 0x400000) |4|2|1;
+    // Next 8MB: Usermode
+    map_pages(0x00800000 >> 12, 1024, 0x00800000, USERACCESS);
+    map_pages(0x00C00000 >> 12, 1024, 0x00C00000, USERACCESS);
 
-    // User, R/W, Present
-    page_directory[0] = ((uintptr_t)first_page_table)|4|2|1;
-    page_directory[1] = ((uintptr_t)second_page_table)|4|2|1;
+    // We aren't using page directory permissions
+    for (int i = 0; i < 4; i++)
+        page_directory[i] = ((uintptr_t)&page_tables[i]) | USERACCESS;
 
     enable_paging();
 }

progs.c

@@ -1,9 +1,7 @@
 #include "progs.h"
 #include "file.h"
 
-// 400000 - 700000 Usermode Code (3mB)
-// 700000 - 800000 Usermode Stack (1mB)
-extern char _USERMODE;
+extern char _USERMODE, _USERMODE_END;
 extern uint32_t create_user_child(uint32_t esp, uint32_t eip, uint32_t argc, ...);
 void ProgramLoadTest(char *path, dirent *de) {
     uint16_t *vga_text = (uint16_t *)0xb8000;
@@ -46,7 +44,7 @@ void ProgramLoadTest(char *path, dirent *de) {
     vga_text = nextLine(vga_text,(uint16_t*)0xb8000);
     vga_text += printStr("Press any key to run.", vga_text);
     kbd_wait();
-    uint32_t res = create_user_child(0x800000, (uintptr_t)&_USERMODE, 0);
+    uint32_t res = create_user_child((uintptr_t)&_USERMODE_END, (uintptr_t)&_USERMODE, 0);
     union V86Regs_t regs;
     regs.w.ax = 3; // text mode
     V8086Int(0x10, &regs); 

task.nasm

@@ -152,17 +152,12 @@ mov ecx, esp ; return stack
 call save_current_task
 _enter_v86_internal_no_task:
 mov ebp, esp               ; save stack pointer
-mov eax, dword [ebp+16] ; regs
-test eax, eax
-jz .no_regs
-; load regs: edi, esi, ebx, edx, ecx, eax
-mov edi, dword [eax+0]
-mov esi, dword [eax+4]
-mov ebx, dword [eax+8]
-mov edx, dword [eax+12]
-mov ecx, dword [eax+16]
-mov eax, dword [eax+20]
-.no_regs:
+; push v86 stuff for iret
+mov eax, 0x3000
+push eax ; gs
+push eax ; fs
+push eax ; ds
+push eax ; es
 push dword  [ebp+0]        ; ss
 push dword  [ebp+4]        ; esp
 pushfd                     ; eflags
@@ -170,6 +165,19 @@ or dword [esp], (1 << 17)  ; set VM flags
 ;or dword [esp], (3 << 12) ; IOPL 3
 push dword [ebp+8]        ; cs
 push dword  [ebp+12]       ; eip
+; check if we have regs
+mov eax, dword [ebp+16] ; regs
+test eax, eax
+jz .no_regs
+; load regs: ebp, edi, esi, ebx, edx, ecx, eax
+mov ebp, dword [eax+0]
+mov edi, dword [eax+4]
+mov esi, dword [eax+8]
+mov ebx, dword [eax+12]
+mov edx, dword [eax+16]
+mov ecx, dword [eax+20]
+mov eax, dword [eax+24]
+.no_regs:
 iret
 
 ; return address in eax, return stack in ebp

testpgrm.nasm

@@ -1,5 +1,5 @@
 [BITS 32]
-[ORG 0x400000]
+[ORG 0x800000]
 xchg bx,bx
 mov edi, 0xB8000
 mov ecx, 80*25

tests.c

@@ -16,7 +16,7 @@ void TestV86() {
     uint16_t *vga_text = (uint16_t *)0xb8000 + (80*2);
     vga_text += printStr("Done.", vga_text);
 }
-extern char _USERMODE;
+extern char _USERMODE, _USERMODE_END;
 extern char _binary_usermode_bin_start, _binary_usermode_bin_end;
 void ReloadUser() {
     // Put Usermode code in proper place based on linker
@@ -27,7 +27,7 @@ void ReloadUser() {
 }
 char TestUser() {
     ReloadUser();
-    char *vga = (char *)(uintptr_t)create_user_child(0x800000, (uintptr_t)&_USERMODE, 0);
+    char *vga = (char *)(uintptr_t)create_user_child((uintptr_t)&_USERMODE_END, (uintptr_t)&_USERMODE, 0);
     if ((uintptr_t)vga != 0xA0000) {
         return 1;
     }

usermode.nasm

@@ -1,5 +1,5 @@
 [BITS 32]
-[ORG 0x400000]
+[ORG 0x800000]
 global user_test
 user_test:
 mov dword [0xb8000], 0x0f000f00 | 'U' | 's' << 16
@@ -43,6 +43,7 @@ push 0x00000000 ; edx
 push 0x00000000 ; ebx
 push 0x00000000 ; esi
 push 0x00000000 ; edi
+push 0x00000000 ; ebp
 push esp ; regs
 push 0x10 ; interrupt
 mov eax, 0x86 ; command = 86h, virtual 8086 call

v86defs.h

@@ -14,6 +14,7 @@ extern void v86DiskReadCHS();
 
 union __attribute((__packed__)) V86Regs_t {
     struct dword_regs { 
+        uint32_t ebp;
         uint32_t edi;
         uint32_t esi;
         uint32_t ebx;
@@ -22,6 +23,7 @@ union __attribute((__packed__)) V86Regs_t {
         uint32_t eax;
     } d;
     struct word_regs { 
+        uint16_t bp, _upper_bp;
         uint16_t di, _upper_di;
         uint16_t si, _upper_si;
         uint16_t bx, _upper_bx;
@@ -30,8 +32,9 @@ union __attribute((__packed__)) V86Regs_t {
         uint16_t ax, _upper_ax;
     } w;
     struct byte_regs { 
-        uint16_t di, _upper_di;
-        uint16_t si, _upper_si;
+        uint32_t ebp;
+        uint32_t edi;
+        uint32_t esi;
         uint8_t bl, bh;
         uint16_t _upper_bx;
         uint8_t dl, dh;