为什么动态链接器会尝试打开它知道不存在的文件？

Question

如果我尝试链接到一个未知的库（-lunknown）并查看（使用strace）来查看链接器正在做什么，我注意到，在stat返回-1后立即（ENOENT），链接器尝试open它刚刚发现的文件不存在。从strace输出中，我们看到：

stat("/usr/bin/../lib/gcc/x86_64-linux-gnu/4.7/libunknown.so", 0x7fff6694df50) = -1 ENOENT (No such file or directory)
open("/usr/bin/../lib/gcc/x86_64-linux-gnu/4.7/libunknown.so", O_RDONLY) = -1 ENOENT (No such file or directory)
stat("/usr/bin/../lib/gcc/x86_64-linux-gnu/4.7/libunknown.a", 0x7fff6694dfb0) = -1 ENOENT (No such file or directory)
open("/usr/bin/../lib/gcc/x86_64-linux-gnu/4.7/libunknown.a", O_RDONLY) = -1 ENOENT (No such file or directory)
... [lots of similar lines here]

ld版本：

$ ld -v
GNU ld (GNU Binutils for Ubuntu) 2.23.2

为什么链接器会在open返回-1后尝试stat？