[binutils-gdb] gdbserver crash if gdb attaches too fast

[sergiodj+buildbot at redhat dot com]

*** TEST RESULTS FOR COMMIT 500c1d8576ad5a5bdc791fc7f7c3518a4d3f4b39 ***

Author: Pedro Alves <palves@redhat.com>
Branch: master
Commit: 500c1d8576ad5a5bdc791fc7f7c3518a4d3f4b39

gdbserver crash if gdb attaches too fast

With "maint set target-non-stop on", the attach tests occasionally
crash gdbserver.

Basically, gdb attaches with vAttach;PID, and then shortly after reads
the xml target description for that process, to figure out the
process' architecture.  On the gdbserver side, the target description
is only filled in when the first process/thread in the thread group
reports its initial PTRACE_ATTACH SIGSTOP.  So if GDB is fast enough,
it can read the target description _before_ that initial stop, and
then gdbserver dies dereferencing a NULL tdesc pointer.

gdb/gdbserver/ChangeLog:
2015-11-30  Pedro Alves  <palves@redhat.com>

	* linux-low.c (linux_attach): In non-stop mode, wait for one stop
	before returning.