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arch/x86/entry/entry_64.S

arch/x86/entry/entry_64.S contains the system-call and fault low-level handling routines.

Notes on argument passing

This source file comments which in which registers arguemnts to syscalls are passed:

rax	system call number
rdi	arg 0
rsi	arg 1
rdx	arg 2
r10	arg 3 (needs to be moved to rcx to conform to C ABI)
r8	arg 4
r9	arg 5
rcx	return address (set by `syscall` instruction`)
r11	saved rflags (set by `syscall` instruction` / note: r11 is callee-clobbered register in C ABI)

Note: r12-r15, rbp, rbx are callee-preserved in C ABI.

entry_SYSCALL_64 is the entry point for 64-bit system calls (syscall instruction?).

This function calls do_syscall_64().

The address of entry_SYSCALL_64 is configured as handler for sys calls in syscall_init().

A newly forked process directly context switches into this function («address»).