GNU/Hurd's readlink system call is partly implemented in userspace, which
also allocates a buffer on the stack for the result, and thus needs one
more path.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Old implementation of realpath allocates a PATH_MAX using alloca for
each symlink in the path, leading to MAXSYMLINKS times PATH_MAX
maximum stack usage.
The test create a symlink with __eloop_threshold() loops and creates
a thread with minimum stack size (obtained through
support_small_stack_thread_attribute). The thread issues a stack
allocations that fill the thread allocated stack minus some slack
plus and the realpath usage (which assumes a bounded stack usage).
If realpath uses more than about 2 * PATH_MAX plus some slack it
triggers a stackoverflow.
Checked on x86_64-linux-gnu and i686-linux-gnu.
Reviewed-by: DJ Delorie <dj@redhat.com>
