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SubjectRe: ioperm() / iopl() irritation
Followup to:  <>
By author: Martin Wilck <>
In newsgroup:
> A short question that may be dumb:
> In the docs on i386 IO protection that I know, it is said that
> the processor ANDs the two protection mechanisms offered by the
> IOPL flag and the io permission bitmap. That is, if IO permissions
> are granted through iopl(), but ports are masked in the IO permission
> bitmap, a segmentation fault should arise.


> Such a situation should be generated by code like this:
> iopl(3);
> ioperm (0,0x1f,1); /* 0x20-0x3ff remain masked */
> c = inb (0x20);
> However on my machine this codse is successful! How is that possible?

Because you have misunderstood how IOPL works.

<> at work, <> in private!
"Unix gives you enough rope to shoot yourself in the foot." <>
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