Hacker News: mbbrutman

New comment by mbbrutman in "Hunting a 34 year old pointer bug in EtherSlip"

mbbrutman — Wed, 22 Apr 2026 14:38:42 +0000

I got lucky here with the compiler detecting the problem given that it wasn't just limited to using a null pointer. Depending on the buffer offset being handed back, it could have hit anywhere in the data segment.

Hunting a 34 year old pointer bug in EtherSlip

mbbrutman — Sun, 19 Apr 2026 21:57:25 +0000

Article URL: https://www.brutman.com/Adventures_In_Code/EtherSlip_ARP/EtherSlip_ARP.html

Comments URL: https://news.ycombinator.com/item?id=47827991

Points: 38

# Comments: 8

New comment by mbbrutman in "The DOS 3.3 sys.com bug hunt"

mbbrutman — Mon, 24 Feb 2025 18:07:02 +0000

Where is that published? I was using Github for references on DOS 4 as 3.3 isn't there yet.

(Thanks in advance!)

New comment by mbbrutman in "The DOS 3.3 Sys.com Bug Hunt"

mbbrutman — Mon, 24 Feb 2025 17:06:01 +0000

I looked at the call before and after to see what they had set the buffer to, and they clearly set the buffer to point into what is code. The executable is only 5KB and it's tiny; they had plenty of space in the segment to use a different part of the segment without purposefully blasting their own code.

While it's common, it was still a terrible practice. If whatever was filling in that buffer changed, they could be blasting more code than they intended. (As indicated in what I wrote, I know it was common if they wanted to reuse the space. Device drivers do something similar when they are done with their init code.)

New comment by mbbrutman in "The DOS 3.3 sys.com bug hunt"

mbbrutman — Mon, 24 Feb 2025 16:21:44 +0000

Some day ... It took me months even just to get around writing up what I found ...

I'm still puzzled by the jump on the segment register values. I need to trace through the entire path.

New comment by mbbrutman in "How to run a DOS-based web server"

mbbrutman — Fri, 22 Dec 2023 02:14:26 +0000

Cute article, but I'm not quite sure how you missed the mTCP HTTPServ program ...

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 15:32:16 +0000

I took 30 seconds of video with the beeping and the screen scrolling for posterity. I'll get it posted somewhere.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 15:31:26 +0000

I'm sure I can go for a few more years until the next patch ...

On a more serious note, the web server is the problem here. I've tried to run long periods of time before but eventually it would crash. I finally found a 10+ year old parsing bug that wasn't handling quoting correctly, and it was some sort of crypto coin mining JSON request that tripped the bug. So even what I thought was bullet proof years ago turned out to be broken by changes in the user traffic.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 15:27:28 +0000

Sadly the project is mostly unrelated to my day job. I started mTCP at least 6 years before joining Google and at most of my time at Google is spent on much less fun things.

On the plus side, when I finally do get around to building a cluster of these and a load balancer I'll know what to do. ;)

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 15:01:19 +0000

Maybe, with some qualifications. A machine that is powered on but serves almost no traffic would also qualify but not be terribly interesting.

I'm just happy it's been surviving the hug of death for 12+ hours now. Given the age and software that might be the true accomplishment.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 06:15:30 +0000

Thanks ... I think people are having time-outs so it's not anywhere near close to perfect, but the machine has been running at 100% for five hours or so now and it is not crashing, so I'm happy.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 06:13:56 +0000

There were several speeds of the V20, including the base version at 5Mhz. Using it as a drop-in replacement and keeping the system clock speed the same the NEC V20 would still give you a 15 to 20% performance bump because it used less clock cycles when executing many insgtructions.

(This machine has not been altered to speed the clock.)

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 05:20:59 +0000

There is a fan internally in the machine, but it was placed to cool the 5.25" floppy drive when it was in use.

I have more open space in this machine because I am using a 3.5" drive instead. I also replaced the original fan with a quieter Noctua. The jrIDE is running naked on the side of the machine because I think it was having heat issues.

In a later iteration of this machine it will get more direct cooling; the slots in the case are kind of restrictive.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 05:05:31 +0000

The machine continues to receive the hug of death .. especially with our friendly Europeans waking up. Have faith, it's still running. (And it's been surviving like this for four hours now.)

I've turned down the logging level a little bit and turned off the beeper. On this machine, a 50ms beep on the motherboard buzzer is 50ms of delay. :)

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 04:00:53 +0000

I bought my first NEC V20 in 1986 or 1987. It was my first time touching the motherboard of a computer which made it nerve wracking, but they were very popular at the time. I bought mine mail order through the Exec PC BBS, which I think was in Chicago.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 02:26:30 +0000

http://floppy.museum also running mTCP HTTPServ, but on 80286 class hardware.

(That was featured earlier this year on HN.)

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 02:18:26 +0000

Yeah, far too much for a little CPU like this. Never mind the horror of trying to port all of the libraries and keep them up to date.

Although there are people are using Apache in front of their vintage computers to terminate SSL for them while still having the vintage computer handle the request.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 01:58:21 +0000

486? Nah. 4.77Mhz NEC V20, which is just slightly faster than an 8088.

This should tide you over: http://www.brutman.com/PCjr/pcjr_web_server.html

The main page is the best link. You might want to try back later after the initial rush; the machine is getting pounded.

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 01:47:45 +0000

The Xircom is pretty bad, as it costs a lot to do the I/O through the parallel port. Just using TCP/IP sockets (no disk access or processing) the machine can send and received about 42KB/sec. A better adapter can do nearly 3x that on the same machine.

Performance measurements here: https://www.brutman.com/mTCP/mTCP_Performance.html

New comment by mbbrutman in "2,500 continuous runtime hours on a 4.77Mhz DOS web server"

mbbrutman — Sat, 15 Jul 2023 01:43:51 +0000

A few things to consider here:

  * It's getting hammered.  I didn't expect it to be this bad.
  * If it can't process things fast enough packets might be dropped.  So the TCP/IP error rates are probably pretty high right now.
  * It's logging all of this crap too ...

Normally it can do the handshake in tens of milliseconds. Right now the load on it is basically "crush." But it's queuing and answering as best as it can.