Function sys_arch_prctl 

pub fn sys_arch_prctl(code: u64, addr: u64) -> Result<u64, SyscallError>

SYS_ARCH_PRCTL (350): Architecture-specific process settings.

Supported operations:

• ARCH_SET_FS (0x1002): Set user-space FS.base (Thread Local Storage).
• ARCH_GET_FS (0x1003): Read current FS.base into *arg.