1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
|
.intel_syntax noprefix
.global copy_page_physical
.global loop_m
copy_page_physical:
push ebx
pushf
cli
mov ebx, [esp+12]
mov ecx, [esp+16]
mov edx, cr0
and edx, 0x7fffffff
mov cr0, edx
mov edx, 1024
.loop:
mov eax, [ebx]
mov [ecx], eax
add ebx, 4
add ecx, 4
dec edx
jnz .loop
mov edx, cr0
or edx, 0x80000000
mov cr0, edx
popf
pop ebx
ret
.extern current_task_TCB
.global TCB
.section .data
.struct 0
TCB:
TCB.ESP:
.space 4
TCB.CR3:
.space 4
TCB.ESP0:
.space 4
.global switch_to_task
.global insert_eip_on_stack
.global internal_fork
.extern create_process
.section .text
internal_fork:
push ebp
mov ecx, esp
mov ebp, esp
mov eax, [ebp+8] # current_task
lea edx, after_internal_fork
push edx
push ecx
push eax
call create_process
add esp, 0xC
cmp eax, 0
jnz internal_fork_ret
mov eax, 1
internal_fork_ret:
pop ebp
ret
after_internal_fork:
pop ebp
mov eax, 0
ret
insert_eip_on_stack:
push ebp
mov ebp, esp
mov eax, [ebp+8] # cr3
mov ecx, [ebp+8+4] # address
mov edx, [ebp+8+4+4] # value
push ebx
mov ebx, cr3
mov cr3, eax
mov [ecx], edx
mov cr3, ebx
pop ebx
pop ebp
ret
# C declaration:
# void switch_to_task(thread_control_block *next_thread);
#
# WARNING: Caller is expected to disable IRQs before calling, and enable IRQs again after function returns
switch_to_task:
# Save previous task's state
# Notes:
# For cdecl; EAX, ECX, and EDX are already saved by the caller and don't need to be saved again
# EIP is already saved on the stack by the caller's "CALL" instruction
# The task isn't able to change CR3 so it doesn't need to be saved
# Segment registers are constants (while running kernel code) so they don't need to be saved
push ebx
push esi
push edi
push ebp
mov edi,[current_task_TCB] # edi = address of the previous task's "thread control block"
mov [edi+TCB.ESP],esp # Save ESP for previous task's kernel stack in the thread's TCB
# Load next task's state
mov esi,[esp+(4+1)*4] # esi = address of the next task's "thread control block" (parameter passed on stack)
mov [current_task_TCB],esi # Current task's TCB is the next task TCB
mov esp,[esi+TCB.ESP] # Load ESP for next task's kernel stack from the thread's TCB
mov eax,[esi+TCB.CR3] # eax = address of page directory for next task
mov ebx,[esi+TCB.ESP0] # ebx = address for the top of the next task's kernel stack
# mov [TSS.ESP0],ebx # Adjust the ESP0 field in the TSS (used by CPU for for CPL=3 -> CPL=0 privilege level changes)
mov ecx,cr3 # ecx = previous task's virtual address space
cmp eax,ecx # Does the virtual address space need to being changed?
je .doneVAS # no, virtual address space is the same, so don't reload it and cause TLB flushes
mov cr3,eax # yes, load the next task's virtual address space
.doneVAS:
pop ebp
pop edi
pop esi
pop ebx
sti
ret # Load next task's EIP from its kernel stack
|
