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arch/x86/include/generated/asm/syscalls_64.h

The content of arch/x86/include/generated/asm/syscalls_64.h basically looks like:

__SYSCALL(0, sys_read)
__SYSCALL(1, sys_write)
__SYSCALL(2, sys_open)
__SYSCALL(3, sys_close)
…

This file is included from arch/x86/entry/syscall_64.c and arch/x86/um/sys_call_table_64.c to provide the values for sys_call_table[].

Different numbering in syscalls_32.h

syscalls_64.h has a different numbering from syscalls_32.h because it was renumbered to optimize it at cachline level.