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intel 386 et al

Started by Hul Tytus September 11, 2019
	Anyone know of a good handbook describing the machine code of Intel's 
386's? A page describing each instruction along with some text about the 
various sequences caused by interupts and descriptions of the various tables 
and "descriptors" and special purpose registers and the effects of "protected 
mode" is the hope. An older text that didn't describe the 64 bit versions 
would be ok, maybe preferable.
	Hummel's book I've seen, but it's more of a lengthy volume than a 
handbook. Any others that aren't so windy?

Hul
Hul Tytus <ht@panix.com> writes:
> Anyone know of a good handbook describing the machine code of Intel's > 386's? A page describing each instruction along with some text about
I don't know if it's exactly the format you wanted, but I liked "Programming the 80386" by John Crawford and Patrick Gelsinger, who were involved with the 386's design. It did a good job of explaining how memory mapping, the protected mode segment registers, call gates for crossing privilege domains etc. all worked. I still don't understand why today's OS's don't use those features. They would also allow application programs to be set up like miniature OS's with protected memory regions, for things like in-memory databases.
On 11.09.2019 23:06, Hul Tytus wrote:
> Anyone know of a good handbook describing the machine code of Intel's > 386's? A page describing each instruction along with some text about the > various sequences caused by interupts and descriptions of the various tables > and "descriptors" and special purpose registers and the effects of "protected > mode" is the hope. An older text that didn't describe the 64 bit versions > would be ok, maybe preferable. > Hummel's book I've seen, but it's more of a lengthy volume than a > handbook. Any others that aren't so windy? >
https://software.intel.com/en-us/articles/intel-sdm
On 11/09/2019 23:27, Paul Rubin wrote:
> Hul Tytus <ht@panix.com> writes: >> Anyone know of a good handbook describing the machine code of Intel's >> 386's? A page describing each instruction along with some text about
I presume this is for some sort of history project?
> > I don't know if it's exactly the format you wanted, but I liked > "Programming the 80386" by John Crawford and Patrick Gelsinger, who were > involved with the 386's design. It did a good job of explaining how > memory mapping, the protected mode segment registers, call gates for > crossing privilege domains etc. all worked. I still don't understand > why today's OS's don't use those features. They would also allow > application programs to be set up like miniature OS's with protected > memory regions, for things like in-memory databases. >
It is a /long/ time since I have read details of the 386 - you are talking about a processor that was outdated over 25 years ago. However, if my memory and understanding is correct, many of these advanced protection features were overly complex and extremely slow. In the days of the 386, there were four main classes of operating systems for it. One was DOS - still popular. Since MS at the time had close to zero concern for security or reliability, it used very little of the protection features, or memory mapping abilities. It did not even use 32-bit modes very much (32-bit DOS extenders were made by third parties). Then there was early Windows. Again, security and protection were not a concern for MS, though they used a couple of features to get multi-tasking of DOS programs. Then there was *nix type systems. These simply did not need the call gates and other bits and pieces for security - all they need are a distinction between user mode and kernel mode, and a way to switch between them. And they didn't need any "virtual" modes or other complications that the 386 provided to let you use old binaries on newer protected systems - you just compiled your *nix code anew for the new system. The complexities of the call gates and other features of the 386 were concepts from a bygone era by the time the 386 came out, and were never of use in the kind of systems used by the 386. And they have no use now either - modern protection rings and hardware virtualisation are massively more efficient, as well as being simpler and more flexible.
Am 11.09.2019 um 23:06 schrieb Hul Tytus:
> Anyone know of a good handbook describing the machine code of Intel's > 386's? A page describing each instruction along with some text about the > various sequences caused by interupts and descriptions of the various tables > and "descriptors" and special purpose registers and the effects of "protected > mode" is the hope. An older text that didn't describe the 64 bit versions > would be ok, maybe preferable.
If you're really looking for just the 386 and not the gazillions of extensions to the Intel 32-bit architecture: in the 90's, we were passing around a file called "386intel.txt", titled "INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986", which explains pretty much everything about the 386. A short search turns up this link for a copy: http://cd.textfiles.com/freedom/CODE/TEXT/386INTEL.ZIP Set your text encoding to cp437, like in the old days. Stefan
Thanks Paul, I take a look at it.

Hul


Paul Rubin <no.email@nospam.invalid> wrote:
> Hul Tytus <ht@panix.com> writes: > > Anyone know of a good handbook describing the machine code of Intel's > > 386's? A page describing each instruction along with some text about
> I don't know if it's exactly the format you wanted, but I liked > "Programming the 80386" by John Crawford and Patrick Gelsinger, who were > involved with the 386's design. It did a good job of explaining how > memory mapping, the protected mode segment registers, call gates for > crossing privilege domains etc. all worked. I still don't understand > why today's OS's don't use those features. They would also allow > application programs to be set up like miniature OS's with protected > memory regions, for things like in-memory databases.
Thanks Stefan, that should be easy to look at.

Hul

Stefan Reuther <stefan.news@arcor.de> wrote:
> Am 11.09.2019 um 23:06 schrieb Hul Tytus: > > Anyone know of a good handbook describing the machine code of Intel's > > 386's? A page describing each instruction along with some text about the > > various sequences caused by interupts and descriptions of the various tables > > and "descriptors" and special purpose registers and the effects of "protected > > mode" is the hope. An older text that didn't describe the 64 bit versions > > would be ok, maybe preferable.
> If you're really looking for just the 386 and not the gazillions of > extensions to the Intel 32-bit architecture: in the 90's, we were > passing around a file called "386intel.txt", titled "INTEL 80386 > PROGRAMMER'S REFERENCE MANUAL 1986", which explains pretty much > everything about the 386.
> A short search turns up this link for a copy: > http://cd.textfiles.com/freedom/CODE/TEXT/386INTEL.ZIP
> Set your text encoding to cp437, like in the old days.
> Stefan
On Thu, 12 Sep 2019 10:37:40 +0200, David Brown wrote:

>On 11/09/2019 23:27, Paul Rubin wrote: >> Hul Tytus <ht@panix.com> writes: >>> Anyone know of a good handbook describing the machine code of Intel's >>> 386's? A page describing each instruction along with some text about > >I presume this is for some sort of history project? > >> >> I don't know if it's exactly the format you wanted, but I liked >> "Programming the 80386" by John Crawford and Patrick Gelsinger, who were >> involved with the 386's design. It did a good job of explaining how >> memory mapping, the protected mode segment registers, call gates for >> crossing privilege domains etc. all worked. I still don't understand >> why today's OS's don't use those features. They would also allow >> application programs to be set up like miniature OS's with protected >> memory regions, for things like in-memory databases. >> > >It is a /long/ time since I have read details of the 386 - you are >talking about a processor that was outdated over 25 years ago. > >However, if my memory and understanding is correct, many of these >advanced protection features were overly complex and extremely slow. > >In the days of the 386, there were four main classes of operating >systems for it. One was DOS - still popular. Since MS at the time had >close to zero concern for security or reliability, it used very little >of the protection features, or memory mapping abilities. It did not >even use 32-bit modes very much (32-bit DOS extenders were made by third >parties). Then there was early Windows. Again, security and protection >were not a concern for MS, though they used a couple of features to get >multi-tasking of DOS programs. Then there was *nix type systems. These >simply did not need the call gates and other bits and pieces for >security - all they need are a distinction between user mode and kernel >mode, and a way to switch between them. And they didn't need any >"virtual" modes or other complications that the 386 provided to let you >use old binaries on newer protected systems - you just compiled your >*nix code anew for the new system.
>The complexities of the call gates and other features of the 386 were >concepts from a bygone era by the time the 386 came out, and were never >of use in the kind of systems used by the 386. And they have no use now >either - modern protection rings and hardware virtualisation are >massively more efficient, as well as being simpler and more flexible.
32 bit OS/2 (and descendants like eCs or ArcaOS) definitely use the call gates. This caused problems with some virtual machines which did not expect that. I don't know anything about the speed differences between call gates and more modern mechanisms. I don't think there were many compilers that supported segments in 32 bit mode (maybe Watcom), so 32 bit is always flat mode. Segments gave you some protection too. Mat Nieuwenhoven
On 13/09/2019 11:37, Mat Nieuwenhoven wrote:
> On Thu, 12 Sep 2019 10:37:40 +0200, David Brown wrote: > >> On 11/09/2019 23:27, Paul Rubin wrote: >>> Hul Tytus <ht@panix.com> writes: >>>> Anyone know of a good handbook describing the machine code of Intel's >>>> 386's? A page describing each instruction along with some text about >> >> I presume this is for some sort of history project? >> >>> >>> I don't know if it's exactly the format you wanted, but I liked >>> "Programming the 80386" by John Crawford and Patrick Gelsinger, who were >>> involved with the 386's design. It did a good job of explaining how >>> memory mapping, the protected mode segment registers, call gates for >>> crossing privilege domains etc. all worked. I still don't understand >>> why today's OS's don't use those features. They would also allow >>> application programs to be set up like miniature OS's with protected >>> memory regions, for things like in-memory databases. >>> >> >> It is a /long/ time since I have read details of the 386 - you are >> talking about a processor that was outdated over 25 years ago. >> >> However, if my memory and understanding is correct, many of these >> advanced protection features were overly complex and extremely slow. >> >> In the days of the 386, there were four main classes of operating >> systems for it. One was DOS - still popular. Since MS at the time had >> close to zero concern for security or reliability, it used very little >> of the protection features, or memory mapping abilities. It did not >> even use 32-bit modes very much (32-bit DOS extenders were made by third >> parties). Then there was early Windows. Again, security and protection >> were not a concern for MS, though they used a couple of features to get >> multi-tasking of DOS programs. Then there was *nix type systems. These >> simply did not need the call gates and other bits and pieces for >> security - all they need are a distinction between user mode and kernel >> mode, and a way to switch between them. And they didn't need any >> "virtual" modes or other complications that the 386 provided to let you >> use old binaries on newer protected systems - you just compiled your >> *nix code anew for the new system. > >> The complexities of the call gates and other features of the 386 were >> concepts from a bygone era by the time the 386 came out, and were never >> of use in the kind of systems used by the 386. And they have no use now >> either - modern protection rings and hardware virtualisation are >> massively more efficient, as well as being simpler and more flexible. > > 32 bit OS/2 (and descendants like eCs or ArcaOS) definitely use the > call gates. This caused problems with some virtual machines which did > not expect that.
OS/2 was written by IBM (at least, those low-level bits were done by IBM. Some of the other bits were done by MS). The IBM's came from a background with bigger systems - mainframes - and liked this kind of powerful hardware feature. So it doesn't surprise me that they used it.
> I don't know anything about the speed differences between call gates > and more modern mechanisms. > I don't think there were many compilers that supported segments in 32 > bit mode (maybe Watcom), so 32 bit is always flat mode. Segments gave > you some protection too. >
I think that is correct, in the days of the 386 at least. But I don't know details there. My PC programming at that time was targetting 16-bit Windows or DOS (although I used OS/2 as the OS).
On Thu, 12 Sep 2019 10:37:40 +0200, David Brown
<david.brown@hesbynett.no> wrote:

>On 11/09/2019 23:27, Paul Rubin wrote: >> Hul Tytus <ht@panix.com> writes: >>> Anyone know of a good handbook describing the machine code of Intel's >>> 386's? A page describing each instruction along with some text about > >I presume this is for some sort of history project? > >> I don't know if it's exactly the format you wanted, but I liked >> "Programming the 80386" by John Crawford and Patrick Gelsinger, who were >> involved with the 386's design. It did a good job of explaining how >> memory mapping, the protected mode segment registers, call gates for >> crossing privilege domains etc. all worked. I still don't understand >> why today's OS's don't use those features. They would also allow >> application programs to be set up like miniature OS's with protected >> memory regions, for things like in-memory databases. >> > >It is a /long/ time since I have read details of the 386 - you are >talking about a processor that was outdated over 25 years ago. > >However, if my memory and understanding is correct, many of these >advanced protection features were overly complex and extremely slow.
That's true ... validating segment descriptors and segment limits when loading the segment selector took > 1000 cycles. This was so onerous that the i486 and later included a small cache of validated descriptors. But the cache never was large enough to help programs that needed to use many segments - IIRC, it held only 6 entries - and as time went on it shrank to just 2 entries. Another problem with segments was there were too few of them available: 8K local (per process) segments is not really enough for fine grain object protection, and 8K global segments is not a whole lot when you consider all the uses the operating system might have. But the biggest problem was that the segment selector was a visible component of addressing. This may have been acceptible on the 8086, but segments there were purely for addressing and had no protection dimension. It became a debate issue starting with the i286, but that chip had so many other issues that segment visibility was lost in the noise. When it was announced that the 80386 would include transparent paging, many people hoped that its segmentation behavior would be rethought. Segment advocates hoped that the conflation of segment selection with addressing would be abandoned, that segments would become protection domains only, that segments would be able to be defined and used more dynamically, and that using them would be made much faster. [I'm not taking any positions on this, I'm just recalling things I saw in media and in Usenet discussions at the time.]
>In the days of the 386, there were four main classes of operating >systems for it. One was DOS - still popular. Since MS at the time had >close to zero concern for security or reliability, it used very little >of the protection features, or memory mapping abilities. It did not >even use 32-bit modes very much (32-bit DOS extenders were made by third >parties). Then there was early Windows. Again, security and protection >were not a concern for MS, though they used a couple of features to get >multi-tasking of DOS programs. Then there was *nix type systems. These >simply did not need the call gates and other bits and pieces for >security - all they need are a distinction between user mode and kernel >mode, and a way to switch between them. And they didn't need any >"virtual" modes or other complications that the 386 provided to let you >use old binaries on newer protected systems - you just compiled your >*nix code anew for the new system. > >The complexities of the call gates and other features of the 386 were >concepts from a bygone era by the time the 386 came out, and were never >of use in the kind of systems used by the 386. And they have no use now >either - modern protection rings and hardware virtualisation are >massively more efficient, as well as being simpler and more flexible.
Agreed, the i286/i386 ring mechanism was complicated to use, but that was because the protected segment mechanism itself was complicated to use. And again, with only 8K global segments, there weren't enough segments available to protect OS services using call gates unless you seriously restricted the number of service entry points [there were a few OSes that did]. YMMV, George