[program-l] Re: assembly help?
- From: "Mike Gorse" <mike@xxxxxxxxxx>
- To: <program-l@xxxxxxxxxxxxx>
- Date: Mon, 9 Jan 2006 10:06:37 -0500
Thanks Mark and Tyler for the help!
----- Original Message -----
From: "Mark Long" <Mark.Long@xxxxxxxxxxxxx>
To: <program-l@xxxxxxxxxxxxx>
Sent: Sunday, January 08, 2006 7:15 AM
Subject: [program-l] Re: assembly help?
Hello Mike
I have a moment now and so I can take a stab at explaining these things.
The instruction sets of the later processors are rather fuller although the
basic operations are as they were. There are a lot of instructions that
pretty much have to be there for a Von Neuman architecture CPU and all
modern CPUs follow this pattern. The biggest changes have been in bus width.
Pretty much everything is 32 bit these days. You can get to individual bytes
if you need to but all transfers are 32 bit so there is no real point most
of the time.
Assembler is hardly ever used these days. Even virus writers mostly use C++
these days. A very small percentage of Windows is written in assembler and
that is mostly in the HAL (Hardware Abstraction Layer). The optimisers on
modern compilers are so good that even a skilled low level programmer
struggles to write such tight code and it is rare to improve performance
much with hand tuning. Even C++ is falling out of use in many areas and
managed code is becoming the norm for applications on Windows.
The best reference that I use is the specification documents that I
downloaded from the intel site. One page per instruction, all effects of the
opcode listed. What more could any programmer want?
Ring 0 access is more commonly called Kernel mode. On Windows, applications
run in ring 3 or user mode. They experience a world of processes and flat
address space where all memory access to bus devices is impossible -
essentially, it is a sandbox. It is a roomy high class sandbox and you can
do a lot of things but anything that you need to do outside of your process
can only be done with system call. Ring 0 is where the drivers and some of
the operating system lives. There is no sandbox there. You can talk directly
to hardware or any part of memory. A lot of the abstractions such as
processes don't really exist down there. Mistakes are dangerous in ring 0.
If your user mode process accesses memory that it shouldn't and there is no
handler then you get a grey box popping up telling you that the process is
being terminated. If you do the same thing in kernel mode then the machine
bluescreens. Only driver writers and OS vendors really live down there. It
is a scary place. There is also a time cost for switching to Kernel mode so
we try to minimise transistions.
Does that help at all?
Mark
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