[9fans] self modifying code in intel vga bios?

[9fans] self modifying code in intel vga bios?

[cinap_lenrek at gmx.de]

Fish- has catched this on a Intel(r)915GM/910ML/915MS Graphics Controller
with realemu:

bad mem write c0c11
bad memory access
1d17b0 4a008800 00000002 00000000 0000a002 00009000 00005108 ac007bda 00007bc0 0000 0000 0000 c000 csZoPdI 61ed c6 MOV CS:[c11], $01

question to the coreboot guys:

did you ever see the bios writing in the rom area? 

i found this quote on: http://www.coreboot.org/VGA_support

"Even if your VGA BIOS uses self-modifying code you get a correct image"

i know that the rom area is usualy cached in ram but to catch mistakes
i disallow writing to the rom area...  fish will make full traces
later this day...  it could be just a screwup on my side...
just curious :)

--
cinap

[9fans] self modifying code in intel vga bios?

[Lucio De Re]

On Tue, Mar 08, 2011 at 10:24:48AM +0100, cinap_lenrek at gmx.de wrote:
> 
> Fish- has catched this on a Intel(r)915GM/910ML/915MS Graphics Controller
> with realemu:
> 
> bad mem write c0c11
> bad memory access
> 1d17b0 4a008800 00000002 00000000 0000a002 00009000 00005108 ac007bda 00007bc0 0000 0000 0000 c000 csZoPdI 61ed c6 MOV CS:[c11], $01
> 
You know it's a crappy architecture when even the manufacturer needs to
use self-modifying code.  I thought self-modifying code (and all its
dangers) had gone out of fashion a few decades ago and more advanced
architectures provided safer ways to provide equivalent functionality.

Heavens, with variable length instructions, the types of bugs this can
give rise to are positively frightening.  A case of "clever but stoopid".

++L

[9fans] self modifying code in intel vga bios?

[ron minnich]

you have to allow for self modifying code. Yes, it's in there.

Great, huh? I love BIOS software.

ron

[9fans] self modifying code in intel vga bios?

[Paul Lalonde]

Today, of course, we'd call this JIT, and shove it in a new page, and think
ourselves clever.
The last time I poked at one of these self-modifying bits they were really
just jitting a blit loop, in place.  Drops register pressure a little bit,
which has always been a bit of an issue in x86 land.

Paul

On Tue, Mar 8, 2011 at 7:03 AM, ron minnich <rminnich at gmail.com> wrote:

> you have to allow for self modifying code. Yes, it's in there.
>
> Great, huh? I love BIOS software.
>
> ron
>
>


-- 
I'm migrating my email.  plalonde at telus.net will soon be disconnected.
 Please use paul.a.lalonde at gmail.com from now on.
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[9fans] self modifying code in intel vga bios?

[Lucio De Re]

On Tue, Mar 08, 2011 at 07:21:50AM -0800, Paul Lalonde wrote:
> The last time I poked at one of these self-modifying bits they were really
> just jitting a blit loop, in place.  Drops register pressure a little bit,
> which has always been a bit of an issue in x86 land.
> 
A bankrupt CPU architecture.  I guess the day they all do it, it will
be decreed "the right way".  In the meantime, I guess we can still
shop around.

++L

[9fans] self modifying code in intel vga bios?

[erik quanstrom]

On Tue Mar  8 10:30:25 EST 2011, lucio at proxima.alt.za wrote:
> On Tue, Mar 08, 2011 at 07:21:50AM -0800, Paul Lalonde wrote:
> > The last time I poked at one of these self-modifying bits they were really
> > just jitting a blit loop, in place.  Drops register pressure a little bit,
> > which has always been a bit of an issue in x86 land.
> > 
> A bankrupt CPU architecture.  I guess the day they all do it, it will
> be decreed "the right way".  In the meantime, I guess we can still
> shop around.

just like ata is no longer a physical spec, x86 is no longer a architecture.
it is simply an instruction set.  i can think of many different architectures
that implement the x86 instruction set you can buy today, for example:
bonnell (atom), athlon64, intel 5000 (conroe and friends), nehalem,
sandy bridge, via c7, etc.  the same thing goes for arm, and power.

you can complain that it's hard to decode x86, but this is also a strength:
x86 has good code density.

imagine the chaos that we'd have if the cpu vendors released a new
instruction set for each new architecture?

it may be that instruction sets aren't very important any longer.

- erik

[9fans] self modifying code in intel vga bios?

[Lucio De Re]

> it may be that instruction sets aren't very important any longer.

I wish I had the persistence to respond to this gem in detail.

What is important, in my opinion, is "progress" in some undefinable,
but recognisable sense.  Faster and faster isn't it and it does seem
to set higher and higher entry barriers for alternatives.  Basically,
that way lies a monopoly that throttles diversification.  Put Nokia in
bed with Microsoft in bed with Intel and you're leaving little room
for somebody with a great idea to get any attention.  A brave new
world, indeed.

++L

[9fans] self modifying code in intel vga bios?

[Wes Kussmaul]

On Tue, 2011-03-08 at 19:34 +0200, Lucio De Re wrote:

> Put Nokia in
> bed with Microsoft in bed with Intel and you're leaving little room
> for somebody with a great idea to get any attention.  A brave new
> world, indeed.

But the Wintel duopoly has cracked, the inevitable fate of all such
aggregations of power. They end up being led by people whose talent does
not match the level of their megalomania and whose insecurity leads them
to flail. Not that putting Windows on ARM is a bad flail, but it does
provoke Intel to retaliate by dropping its requirement that
manufacturers accompany X86 chips on laptops and desktops with a Windows
license.

Remember when nothing could possibly dislodge the VAX/VMS hegemony?

Pride cometh before a fall.

Wes