* Gabriel Krisman Bertazi: > +Interface > +--------- > + > +A process can setup this mechanism on supported kernels > +CONFIG_SYSCALL_USER_DISPATCH) by executing the following prctl: > + > + prctl(PR_SET_SYSCALL_USER_DISPATCH, <op>, <offset>, <length>, [selector]) > + > +<op> is either PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF, to enable and > +disable the mechanism globally for that thread. When > +PR_SYS_DISPATCH_OFF is used, the other fields must be zero. > + > +<offset> and <offset+length> delimit a closed memory region interval > +from which syscalls are always executed directly, regardless of the > +userspace selector. This provides a fast path for the C library, which > +includes the most common syscall dispatchers in the native code > +applications, and also provides a way for the signal handler to return > +without triggering a nested SIGSYS on (rt_)sigreturn. Users of this > +interface should make sure that at least the signal trampoline code is > +included in this region. In addition, for syscalls that implement the > +trampoline code on the vDSO, that trampoline is never intercepted. > + > +[selector] is a pointer to a char-sized region in the process memory > +region, that provides a quick way to enable disable syscall redirection > +thread-wide, without the need to invoke the kernel directly. selector > +can be set to PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF. Any other > +value should terminate the program with a SIGSYS.
Is this a process property or a task/thread property? The last paragraph says “thread-wide”, but the first paragraph says “process”.
