There were two issues with signal handling:
- With a kernel stack the "info" parameter was passed from kernel memory.
This is fixed by making a stack frame to the user stack and copying it
there.
- If the signal handler uses a system call, the kernel stack was completely
and unconditionally destroyed, resulting in a crash in the user application
There is also no need to check ustkptr, it is always NULL. Why ? Because
signal delivery is deferred when a system call is being executed.
686b990a85