vdso的全称是virtual dynamic shared object的全称，比vsyscall 安全。从vsdo.lds.s中可以
看到目前vsdo 支持下面四个系统调用

/*
 * This controls what symbols we export from the DSO.
 */
VERSION
{
	LINUX_2.6.39 {
	global:
		__kernel_rt_sigreturn;
		__kernel_gettimeofday;
		__kernel_clock_gettime;
		__kernel_clock_getres;
	local: *;
	};
}

可以看到vdso

linux-rm3j:/boot/grub2 # cat /proc/self/maps
aaaab7a7b000-aaaab7a83000 r-xp 00000000 00:2d 30103                      /usr/bin/cat
aaaab7a9a000-aaaab7a9b000 r--p 0000f000 00:2d 30103                      /usr/bin/cat
aaaab7a9b000-aaaab7a9c000 rw-p 00010000 00:2d 30103                      /usr/bin/cat
aaaabcde2000-aaaabce03000 rw-p 00000000 00:00 0                          [heap]
ffffa6c0f000-ffffa6c11000 rw-p 00000000 00:00 0
ffffa6c11000-ffffa6c12000 r--p 00000000 00:00 0                          [vvar]
ffffa6c12000-ffffa6c13000 r-xp 00000000 00:00 0                          [vdso]