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=={{header|X86 Assembly}}== |
=={{header|X86 Assembly}}== |
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I've written a subroutine that prints out any positive value. It lives on my desktop and you can't find it on rosetta code. |
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{{works with|NASM|Linux}}<br> |
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I've also written a sleep subroutine and you can find that in the Sleep task on this site. |
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While it IS possible to use native syscalls to create forks, it's not recommended. sys_fork requires manual setup for the pt_regs structure. It further requires you to enter kernal space using sysenter/exit pairs, setup the registers then call sys_fork. Linking to the C library is simply less work for user space forks. The only time it's really used is during debugging applications. |
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<lang asm> |
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<lang x86asm> |
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extern fork |
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; x86_64 linux nasm |
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extern printf |
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%include "/home/james/Desktop/ASM_LIB/Print.asm" |
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%include "/home/james/Desktop/ASM_LIB/Sleep.asm" |
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section .text |
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global _start |
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_start: |
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call fork |
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cmp eax, 0 |
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je _child |
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jg _parent |
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jmp _exit |
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_parent: |
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push p_msg |
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call printf |
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jmp _exit |
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_child: |
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push c_msg |
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call printf |
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jmp _exit |
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_exit: |
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push 0x1 |
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mov eax, 1 |
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push eax |
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int 0x80 |
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ret |
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section .data |
section .data |
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c_msg db "Printed from Child process",13,10,0 |
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parent: db "Parent: " |
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child: db "Child: " |
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newLine: db 10 |
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section .text |
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global _start |
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_start: |
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mov rax, 57 ; fork syscall |
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syscall |
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cmp rax, 0 ; if the return value is 0, we're in the child process |
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je printChild |
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printParent: ; else it's the child's PID, we're in the parent |
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mov rax, 1 |
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mov rdi, 1 |
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mov rsi, parent |
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mov rdx, 8 |
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syscall |
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mov rax, 39 ; sys_getpid |
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syscall |
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mov rdi, rax |
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call Print_Unsigned |
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mov rax, 1 |
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mov rdi, 1 |
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mov rsi, newLine |
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mov rdx, 1 |
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syscall |
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mov rdi, 1 ; sleep so the child process can print befor the parent exits |
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call Sleep ; you might not see the child output if you don't do this |
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jmp exit |
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printChild: |
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mov rdi, 1 |
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call Sleep ; sleep and wait for parent to print to screen first |
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mov rax, 1 |
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mov rdi, 1 |
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mov rsi, child |
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mov rdx, 7 |
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syscall |
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mov rax, 39 ; sys_getpid |
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syscall |
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mov rdi, rax |
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call Print_Unsigned |
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mov rax, 1 |
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mov rdi, 1 |
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mov rsi, newLine |
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mov rdx, 1 |
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syscall |
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exit: |
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mov rax, 60 |
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mov rdi, 0 |
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syscall |
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</lang> |
</lang> |
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