When used gdb on UML, I met several problems:
1) When i startup gdb on UML, I got the error message: Couldn't write debug register:Input/output error.
2) When fork function is executed, I got the error message: thread_get_info_callback: cannot get thread info: generic error, and the gdb was hang.
3) When I debug multiple-thread program, gdb cannot catch the other thread. When i tried to use the cmd: thread <THREADID> to catch the other thread, segmentation fault occured.

BTW: When not on UML but linux server, these problems never occured when I did the same operations.

Who can help me? I have been blocked by these problems for a long time.

because what you said went over my head
all i can say is are you sue your copy of gdb is good?

When I made the rootfs for UML and installed the gdb rpm, there is one and only one error(error:%post(iputils-20020927-21.el4.x86_64) scriptlet failed, exit status 127)). I am not sure if the error will cause gdb this problem.

BTW: my gdb version is 6.3.0.0, I had ever tried to install gdb6.8 through making source code but rpm, and met the same problem.