notes

Looks like the problem is here:

arch/x86-32/arch_scheduler.asm:255

; void INT_80_test(void);
INT_80_test:
    pushad

    ; System call: write(int fd, const char *buf, size_t count)
    ; eax = 4 (sys_write)
    ; ebx = file descriptor (1 for stdout)
    ; ecx = pointer to message
    ; edx = length of message

    mov eax, 4                     ; sys_write system call number
    mov ebx, 1                     ; file descriptor 1 (stdout)
    mov ecx, msg_int80_test
    mov edx, msg_int80_test_len
    int 0x80                       ; make system call using int 0x80

    popad       <----------- After returning from int0x80, and poping registers, the return address is 0 !!!
    ret

THE PROBLEM:
    The problem (most likely) is that existing manual schedule()/switch_process() assumes existence of
    the return address as the last value on the stack, while IRQ version saves the SP without the IRQ part of the stack, 
    and when doing iret, it just creates necessary stack values to use "iret" for context switching
    That means when restoring ctx with switch_process(), that was saved in IRQ contex, the last value on stack will be overwritten

        - The fix would be for schedule()/switch_process() to save SP without return address and push it to the stack before "ret"
            - Then I need to save PC and push it to the stack befor 'ret'. 
                - Just save the PC from the return address, that would be the most natural way

What I can do:
    - When debugging, check the value of "current_process_index" to see what is current active process
    - Add code for printing debug info:
        - after call to move_to_next_process() (but only for schedule_in_irq_context)
            - print all registers of the struct process_ctx
            - print the stack content by 32-bit values of the sp pointed by struct process_ctx



--------------------------------------------------------

Starting kernel... 

kernel_c_main():  entry addr      = 0x102e7b 
kernel_c_main():  STACK_MEM_START = 0x206e90 
kernel_c_main():  &local_var      = 0x206e3c 
kernel_c_main():  &hello_msg      = 0x206e29 
kernel_c_main():  STACK_MEM_END   = 0x106e90 

Stack unittests: PASSED
Memory allocator unittests: PASSED
Parsing BIOS Data Area...
COM1 I/O Port: 0x03F8
LPT1 I/O Port: 0x0378
Loading initial RAM disk: SUCCESS

Called scheduler_init()
Called init_process()
init_process(): Created process "Test process" 
init_process():   entry = 0x102e2a 
init_process():   stack = 0x1e0000 
init_process():   SP    = 0x1dffd8 



-----[ Just before call to <switch_process> ]-----

(gdb) disassemble
Dump of assembler code for function schedule:
   0x00102cb8 <+0>:     push   ebp
   0x00102cb9 <+1>:     mov    ebp,esp
   0x00102cbb <+3>:     push   ebx
   0x00102cbc <+4>:     sub    esp,0x14
   0x00102cbf <+7>:     call   0x10573c <__x86.get_pc_thunk.bx>
   0x00102cc4 <+12>:    add    ebx,0x2f00
   0x00102cca <+18>:    mov    eax,DWORD PTR [ebx+0x109c]
   0x00102cd0 <+24>:    mov    DWORD PTR [ebp-0x10],eax
   0x00102cd3 <+27>:    mov    DWORD PTR [ebp-0xc],0x0
   0x00102cda <+34>:    mov    edx,DWORD PTR [ebx+0x109c]
   0x00102ce0 <+40>:    lea    eax,[ebx+0x10a0]
   0x00102ce6 <+46>:    cmp    edx,eax
   0x00102ce8 <+48>:    jne    0x102cf5 <schedule+61>
   0x00102cea <+50>:    lea    eax,[ebx+0x10a8]
   0x00102cf0 <+56>:    mov    DWORD PTR [ebp-0xc],eax
   0x00102cf3 <+59>:    jmp    0x102cfe <schedule+70>
   0x00102cf5 <+61>:    lea    eax,[ebx+0x10a0]
   0x00102cfb <+67>:    mov    DWORD PTR [ebp-0xc],eax
   0x00102cfe <+70>:    sub    esp,0x8
   0x00102d01 <+73>:    push   DWORD PTR [ebp-0xc]
   0x00102d04 <+76>:    push   DWORD PTR [ebp-0x10]
=> 0x00102d07 <+79>:    call   0x103dab <switch_process>
   0x00102d0c <+84>:    add    esp,0x10
   0x00102d0f <+87>:    lea    eax,[ebx-0x2e9d]
   0x00102d15 <+93>:    mov    DWORD PTR [ebp-0x14],eax
   0x00102d18 <+96>:    mov    eax,DWORD PTR [ebp-0xc]
   0x00102d1b <+99>:    mov    DWORD PTR [ebx+0x109c],eax
   0x00102d21 <+105>:   nop
   0x00102d22 <+106>:   mov    ebx,DWORD PTR [ebp-0x4]
   0x00102d25 <+109>:   leave
   0x00102d26 <+110>:   ret

(gdb) x/32x $sp
0x206df0:       0x00106c64      0x00106c6c      0x00206e18      0x00102cc4
0x206e00:       0x00106c6c      0x00105bc4      0x00106c64      0x00106c6c
0x206e10:       0x0000000d      0x00105bc4      0x00206e48      0x00103051
0x206e20:       0x00000000      0x00000000      0x6c654800      0x66206f6c
0x206e30:       0x206d6f72      0x6f632043      0x00216564      0x00000000
0x206e40:       0x00000000      0x0002cd80      0x00206e50      0x00103e69
0x206e50:       0x00000000      0x00000000      0x00000000      0x00000000
0x206e60:       0x00000000      0x00000000      0x00000000      0x00000000

(gdb) info registers
eax            0x106c6c            1076332
ecx            0x0                 0
edx            0x106c64            1076324
ebx            0x105bc4            1072068
esp            0x206df0            0x206df0
ebp            0x206e18            0x206e18
esi            0x103e3b            1064507
edi            0xb8036             753718
eip            0x102d07            0x102d07 <schedule+79>
eflags         0x12                [ IOPL=0 AF ]

------

(gdb) disassemble
Dump of assembler code for function switch_process:
=> 0x00103dab <+0>:     pusha
   0x00103dac <+1>:     pushf
   0x00103dad <+2>:     mov    eax,DWORD PTR [esp+0x28]
   0x00103db1 <+6>:     mov    DWORD PTR [eax],esp
   0x00103db3 <+8>:     mov    eax,DWORD PTR [esp+0x2c]
   0x00103db7 <+12>:    mov    esp,DWORD PTR [eax]
   0x00103db9 <+14>:    popf
   0x00103dba <+15>:    popa
   0x00103dbb <+16>:    ret

(gdb) x/32x $sp
0x206dec:       0x00102d0c      0x00106c64      0x00106c6c      0x00206e18
0x206dfc:       0x00102cc4      0x00106c6c      0x00105bc4      0x00106c64
0x206e0c:       0x00106c6c      0x0000000d      0x00105bc4      0x00206e48
0x206e1c:       0x00103051      0x00000000      0x00000000      0x6c654800
0x206e2c:       0x66206f6c      0x206d6f72      0x6f632043      0x00216564
0x206e3c:       0x00000000      0x00000000      0x0002cd80      0x00206e50
0x206e4c:       0x00103e69      0x00000000      0x00000000      0x00000000
0x206e5c:       0x00000000      0x00000000      0x00000000      0x00000000

(gdb) info registers
eax            0x106c6c            1076332
ecx            0x0                 0
edx            0x106c64            1076324
ebx            0x105bc4            1072068
esp            0x206dec            0x206dec
ebp            0x206e18            0x206e18
esi            0x103e3b            1064507
edi            0xb8036             753718
eip            0x103dab            0x103dab <switch_process>
eflags         0x12                [ IOPL=0 AF ]

(gdb) bt full
#0  0x00103dab in switch_process ()
#1  0x00102d0c in schedule () at kernel_main.c:242
        process_to_save = 0x106c64 <kernel_process>
        process_to_restore = 0x106c6c <test_process>
        end_of_func_ptr = 0x105bc4
#2  0x00103051 in kernel_c_main () at kernel_main.c:382

------



----- After "pusha" -----

sp = 0x206dcc
ip = 0x103dac

----- After "pushf" -----

sp = 0x206dc8

----- mov eax, [esp+0x28] -----

eax = 0x106c64

----- move [eax], esp -----

- saved SP into proc_to_save

----- mov eax, [esp+0x2c] -----

eax = 0x106c6c
sp  = 0x206dc8


----- mov sp, [eax] -----

sp = 0x1dffd8

(gdb) x/32x $sp
0x1dffd8:       0x00000002      0x00000000      0x00000000      0x00000000
0x1dffe8:       0x00000000      0x00000000      0x00000000      0x00000000
0x1dfff8:       0x00000000      0x001e0000      0x00102e2a      0x00000000
0x1e0008:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e0018:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e0028:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e0038:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e0048:       0x00000000      0x00000000      0x00000000      0x00000000

(gdb) bt full
#0  0x00103db9 in switch_process ()
No symbol table info available.
#1  0x00000002 in ?? ()
No symbol table info available.
#2  0x00103051 in kernel_c_main () at kernel_main.c:382

----- popf -----

sp = 0x1dffdc

(gdb) x/32x $sp
0x1dffdc:       0x00000000      0x00000000      0x00000000      0x00000000
0x1dffec:       0x00000000      0x00000000      0x00000000      0x00000000
0x1dfffc:       0x001e0000      0x00102e2a      0x00000000      0x00000000
0x1e000c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e001c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e002c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e003c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e004c:       0x00000000      0x00000000      0x00000000      0x00000000

(gdb)  bt full
#0  0x00103dba in switch_process ()
No symbol table info available.
#1  0x00000000 in ?? ()
No symbol table info available.

----- popa -----

sp = 0x1dfffc

(gdb) x/32x $sp

(gdb) x/32x $sp
0x1dfffc:       0x001e0000      0x00102e2a      0x00000000      0x00000000
0x1e000c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e001c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e002c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e003c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e004c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e005c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e006c:       0x00000000      0x00000000      0x00000000      0x00000000

(gdb) bt full
#0  0x00103dbb in switch_process ()
No symbol table info available.
#1  0x001e0000 in STACK_MEM_END ()
No symbol table info available.


(gdb) disassemble
Dump of assembler code for function switch_process:
   0x00103dab <+0>:     pusha
   0x00103dac <+1>:     pushf
   0x00103dad <+2>:     mov    eax,DWORD PTR [esp+0x28]
   0x00103db1 <+6>:     mov    DWORD PTR [eax],esp
   0x00103db3 <+8>:     mov    eax,DWORD PTR [esp+0x2c]
   0x00103db7 <+12>:    mov    esp,DWORD PTR [eax]
   0x00103db9 <+14>:    popf
   0x00103dba <+15>:    popa
=> 0x00103dbb <+16>:    ret
End of assembler dump.


----- ret -----

sp = 0x1e0000
ip = 0x1e0000

(gdb) bt full
#0  0x001e0000 in STACK_MEM_END ()
No symbol table info available.
(gdb) info registers
eax            0x0                 0
ecx            0x0                 0
edx            0x0                 0
ebx            0x0                 0
esp            0x1e0000            0x1e0000
ebp            0x0                 0x0
esi            0x0                 0
edi            0x0                 0
eip            0x1e0000            0x1e0000
eflags         0x2                 [ IOPL=0 ]


(gdb) disassemble
Dump of assembler code for function STACK_MEM_END:
   0x00106e90:  add    BYTE PTR [eax],al
   0x00106e92:  add    BYTE PTR [eax],al
   0x00106e94:  add    BYTE PTR [eax],al
   0x00106e96:  add    BYTE PTR [eax],al
   0x00106e98:  add    BYTE PTR [eax],al
   0x00106e9a:  add    BYTE PTR [eax],al
   0x00106e9c:  add    BYTE PTR [eax],al

(gdb) bt full
#0  0x001e0000 in STACK_MEM_END ()
No symbol table info available.












----------
!!! DONE WITH OLD CODE WHERE proc_to_save/restore have diferent address !!!

proc_to_save    = 0x106c44
proc_to_restore = 0x106c4c

sp = 0x206dcc   - ret address
                - proc_to_save
                - proc_to_restore

// After "pusha"

sp = 0x206dac

// After "pushf"

sp = 0x206da8

// mov eax, [esp+0x28]

eax = 0x106c44

// move [eax], esp

- saved SP into proc_to_save

// mov eax, [esp+0x2c]

eax = 0x106c4c
sp  = 0x206da8


// mov sp, [eax]

sp = 0x1dffd8

// popf

sp = 0x1dffdc

0x1dffdc:       0x00000000      0x00000000      0x00000000      0x00000000
0x1dffec:       0x00000000      0x00000000      0x00000000      0x00000000
0x1dfffc:       0x001e0000      0x00102e15      0x00000000      0x00000000
0x1e000c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e001c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e002c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e003c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e004c:       0x00000000      0x00000000      0x00000000      0x00000000

// popa

sp = 0x1dfffc

(gdb) x/32x $sp
0x1dfffc:       0x001e0000      0x00102e15      0x00000000      0x00000000
0x1e000c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e001c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e002c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e003c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e004c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e005c:       0x00000000      0x00000000      0x00000000      0x00000000
0x1e006c:       0x00000000      0x00000000      0x00000000      0x00000000

(gdb) bt full
#0  0x00103dab in switch_process ()
No symbol table info available.
#1  0x001e0000 in STACK_MEM_END ()
No symbol table info available.

(gdb) disassemble
Dump of assembler code for function switch_process:
   0x00103d9b <+0>:     pusha
   0x00103d9c <+1>:     pushf
   0x00103d9d <+2>:     mov    eax,DWORD PTR [esp+0x28]
   0x00103da1 <+6>:     mov    DWORD PTR [eax],esp
   0x00103da3 <+8>:     mov    eax,DWORD PTR [esp+0x2c]
   0x00103da7 <+12>:    mov    esp,DWORD PTR [eax]
   0x00103da9 <+14>:    popf
   0x00103daa <+15>:    popa
=> 0x00103dab <+16>:    ret




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