Interrupts, hardware exceptions, and signals

> Whats the difference between Interrupts, hardware exceptions, and 
> signals 

Interrupts and signals are somehow similar, there is however one 
major difference between them. An interrupt is sent by the 
hardware, and is handled by the kernel. A signal is sent by the 
kernel and is handled by the user mode program. 

They can both be blocked if necesarry, a user mode program can 
use a system call to block signals. The kernel can use special 
instructions and access the IRQ controller to block IRQs. 


What do you have in mind, when you say hardware exceptions? If 
a piece of code does something impossible or just something it 
is just not allowed to, the CPU will generate an exception. 

Exception handling is similar to interrupt handling, but there 
are a few major differences. First of all the interrupt is 
generated by the hardware, and the exception is generated by 
code running on the CPU. This makes the exception a 
synchronous even and the interrupt an asynchronous event. 
This difference also means that exceptions cannot be blocked, 
it wouldn't make any sense since the code causing the 
exception cannot continue before it has been handled. 

When an exception is caused it must be handled by the kernel. 
Sometimes the kernel just have to do something before the 
program can be allowed to continue like copying a page, or 
maybe loading it from disk. Other times the kernel will need 
to generate a signal for the process, or kill it if no handler 
is available. 

-- 
Kasper Dupont