Why does user function is not printing system call message?
Posted: Tue Jun 17, 2025 10:00 am
I am loading a elf file by Limine at Lower half Memory address(0x401000) and initialize MSR based System call (It is working when I am calling it from Kernel mode)as well as interrupt based System Call(But I do not know why t is not working now). I checked the user program can raise other exception like division by zero etc. But Below code I have included syscall instruction nothing is printing.
Why do I not receiving "Hello from user via syscall!" ?
Output:
Thankyou.
syscal_manager.c
syscal_entry.asm
load_and_parse_elf.c
switch_user.asm
Code: Select all
[BITS 64]
global _start
section .text
_start:
; syscall(SYSCALL_PRINT, (uint64_t)msg, 0)
mov rax, 1 ; SYSCALL_PRINT = 1
lea rdi, [rel msg] ; First argument: pointer to message
xor rsi, rsi ; Second argument (not used)
syscall ; Perform syscall
; syscall(SYSCALL_EXIT, 0, 0)
mov rax, 3 ; SYSCALL_EXIT = 3
xor rdi, rdi ; First argument: exit code 0
xor rsi, rsi ; Second argument (unused)
syscall ; Exit syscall
.hang:
jmp .hang ; If syscall fails, loop forever
section .data
msg: db "Hello from user via syscall!", 0
Output:
Code: Select all
Test Address: 0xFFFF800000401000, Value: 0
Page: present=1, rw=1, user=1, frame=0x100C10000, nx=0
Test Address: 0xFFFF800000401000, Value: 12345
Page: present=1, rw=1, user=1, frame=0x100C10000, nx=0
Test Address: 0x401000, Value: 12345
Page: present=1, rw=1, user=1, frame=0x100C10000, nx=0
Test Address: 0x401000, Value: 12345
Page: present=1, rw=1, user=1, frame=0x100C10000, nx=0
Module Path : /boot/user_program.elf
Module Address : 0xFFFF80017FFFE000
Module Size : 5 KB
Module Media Type : 1
Module Partition Index : 0
Module MBR Disk ID : 1069677400
user_program.elf base addr 0xFFFF80017FFFE000
Switching into usermode: user_entry_addr-0x401000, user_stack_addr-0x1000
V. addr: 0x401000, Page: present=1, rw=1, user=1, frame=0x100C10000
syscal_manager.c
syscal_entry.asm
load_and_parse_elf.c
switch_user.asm