The kernel calls perform functions such as setting interrupts and copying data between address spaces.
2.
They have to make kernel calls for these services and the kernel checks each call for authority.
3.
It also supports an API of about 30 kernel calls that authorized servers and drivers can make.
4.
Instead, they must make kernel calls giving a list of I / O ports to write to and the values to be written.
5.
It's generally possible to intercept kernel calls, and to give Warden fake ( i . e . okay ) copies of pages ( ones you've patched ) when it tries to mmap.
6.
It also has a " run to completion " scheduler, which means that the kernel does not pre-empt a running process the process must make a kernel call before other processes get a chance to run.
7.
A process itself can change what these ( often by calling freopen ) but changing another process'( p ) ttys isn't easy; there isn't a kernel call to do this ( but more later ).
8.
The kernel has a lot more leeway in when it delivers user-mode signals, and could arrange to do it only when reentrant kernel calls are safe, but it can't guarantee that user-mode libraries are in a sane state, so signal handlers also have to be very careful about what they call .-- talk ) 00 : 28, 2 February 2015 ( UTC)
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