Assembly - System Call

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OS - System Call (Process OS communication)

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Definition

• Put the system call number in the EAX register.
• Put the arguments:
  • if =< 6, in order in the following register: EBX, ECX, EDX, ESI, EDI, and EBP
  • If >6, the memory location of the first argument is stored in the EBX register.
• Call the relevant interrupt (0x80).
• The result if any is returned in the EAX register.

Implementation

wiki/Interrupt_handler

Example

Exit

; ''1'' = ''sys_exit''
mov	eax,1		
; call kernel
int	0x80

List

Linux

X86 System call tables:

• https://github.com/torvalds/linux/tree/master/arch/x86/entry/syscalls
• 32 https://github.com/torvalds/linux/blob/master/arch/x86/entry/syscalls/syscall_32.tbl

Signature and function definition:

• https://github.com/torvalds/linux/blob/master/include/linux/syscalls.h

wiki/Unistd.h - list the system call but the id number is not the same that in the call tables.

• Code:
  • Generic architecture: https://github.com/torvalds/linux/blob/master/include/uapi/asm-generic/unistd.h
  • x86 architecture: https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/unistd.h
  • arm64: https://github.com/torvalds/linux/blob/master/arch/arm64/include/asm/unistd32.h

Doc:

• https://www.kernel.org/doc/html/v4.13/process/adding-syscalls.html

Doc Linux :

• https://www.kernel.org/doc/html/v4.13/index.html
• Source: https://github.com/torvalds/linux/tree/master/Documentation