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From
SubjectRe: what is wrong with this?
Date
Followup to:  <Mutt.19970106024153.todd@LightHouse.localhost>
By author: friest@acm.org (Todd T. Fries)
In newsgroup: linux.dev.kernel
>
> #include <asm/io.h>
> void main()
> {
> long port;
> short data;
>
> port = 0x8370;
> data = 0;
> iopl(3);
> (*(volatile unsigned short *)(port))=0;
> }
>
> running this as root should not segv. However, it does. Why?
>
> tried linux 2.1.14 and 2.1.20...
>

Sure it should... you're writing into null memory (on Linux, the first
megabyte of memory is unmapped to catch null pointer references.) If
you want to access I/O ports use the I/O functions:

out[bwl](val,port) out[bwl]_p(val,port) in[bwl](port) in[bwl]_p(port)

-hpa

--
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