Linux Arch_prctl的用例是什么

当我在下面这样相当简单的东西上运行strace时，会有2次对arch_prctl的调用.他们干些什么？

$ strace echo "testing 123"
execve("/usr/bin/echo", ["echo", "testing 123"], 0x7ffd396e6c78 /* 61 vars */) = 0
brk(NULL)                               = 0x55e988289000
arch_prctl(0x3001 /* ARCH_??? */, 0x7fff0c166400) = -1 EINVAL (Invalid argument)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=114959, ...}, AT_EMPTY_PATH) = 0
mmap(NULL, 114959, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f5c04879000
close(3)                                = 0
openat(AT_FDCWD, "/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0 \203\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
newfstatat(3, "", {st_mode=S_IFREG|0755, st_size=2250400, ...}, AT_EMPTY_PATH) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5c04877000
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
mmap(NULL, 1973104, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f5c04695000
mmap(0x7f5c046bb000, 1441792, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x26000) = 0x7f5c046bb000
mmap(0x7f5c0481b000, 319488, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x186000) = 0x7f5c0481b000
mmap(0x7f5c04869000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1d3000) = 0x7f5c04869000
mmap(0x7f5c0486f000, 31600, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f5c0486f000
close(3)                                = 0
mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5c04692000
arch_prctl(ARCH_SET_FS, 0x7f5c04692740) = 0
... <more syscalls>