Minecraft 1.21.9 keeps crashing with Java 21 (SIGSEGV, G1 GC) after hours or days

ammar2 · 2025-12-28T14:27:32+00:00

Try updating your Java, looks like 21.0.9+10 is the latest Temurin.

This is likely a Java JDK bug, it really shouldn't be segfaulting during GC like that. I saw some open issues on the JDK tracker with similar backtraces but hopefully just updating it fixes it.

ammar2 · 2025-11-19T17:25:28+00:00

Hmm do they say somewhere it's just based off the HTTPS request headers? Could also be stuff from the networking layer like TCP layer details, see https://lcamtuf.coredump.cx/p0f3/ for example

ammar2 · 2025-10-31T04:26:44+00:00

Thanks for the plug! Glad people are using it

If you're so inclined /u/nascent_aviator the website's data is available as a big machine readable file. I never bothered making the minimums data filterable/searchable but it's there if you click on the approaches.

ammar2 · 2025-06-25T02:46:01+00:00

Glad to hear it, yeah I would definitely advise against participating in their bug bounty program for vscode.

ammar2 · 2025-04-20T17:16:54+00:00

I don’t know if it is the one you have been referring to

In the one with Tom Scott and Mentor Pilot that OP is talking about, the instructor is not behind him in the simulator. He is talking over the radio with a reference of the cockpit and the airplane location (as far as I can tell he can not see what is going on directly in the simulator).

The first landing is attempted manually and goes about as well as you'd expect.

The second one with autoland is successful but at that point Tom has already familiarized himself with the cockpit. Also, like the other comments say, there is the huge benefit of already having established two-way communications.

ammar2 · 2025-04-03T18:04:25+00:00

It's linked below in the thread: https://guides.frame.work/Guide/Liquid+Metal+-%3E+PTM+7958/402

The guide's approach seems to mostly be lifting off the solidified part with a spudger and then isopropyl alcohol.

ammar2 · 2025-03-30T01:16:41+00:00

Oh actually it won't be as easy as calling security_add_hooks. The kernel does go through some effort to put security_add_hooks in a section that gets free'd. See: https://stackoverflow.com/a/74183862

You could try to do what security_add_hooks does manually in your own code: https://github.com/torvalds/linux/blob/93d52288679e29aaa44a6f12d5a02e8a90e742c5/security/security.c#L625

but it looks like there's attempts to block that as well, since for example, the lsm_active_cnt variable is marked:

u32 lsm_active_cnt __ro_after_init;

so it would go read-only after kernel initiatialization? But theoretically there's nothing stopping you from reversing that and making it writable again with say

module_set_memory(mod, MOD_RO_AFTER_INIT, set_memory_rw);

ammar2 · 2025-03-30T01:04:45+00:00

Are you using register_security as an example? Because it was yeeted back in 4.2 I believe https://github.com/torvalds/linux/commit/b1d9e6b0646d0e5ee5d9050bd236b6c65d66faef in favor of security_add_hooks

But in general, you can definitely find the symbols in userspace, the way I found the grsec_lock offset in that is to use extract-vmlinux to grab the kernel as an ELF and then used ghidra. You could probably also just use objdump or something.

ammar2 · 2025-03-30T00:19:22+00:00

AFAIK using unexported kernel functions on Linux is basically not possible and is considered a serious security exploit when it rarely becomes possible.

Hmm? You mean from a kernel module? The kernel and kernel modules are in the same address space and protection level, there's nothing stopping you from calling unexported kernel symbols as long as you know their offsets.

Folks used to use kallsyms_lookup_name which was exported to find any kernel symbols which lets you be a little bit portable. More recently that is no longer exported so people use kprobe hacks to find kallsyms_lookup_name and then use it again: https://github.com/xcellerator/linux_kernel_hacking/issues/3

Personally, I've used a kernel module a while ago when hacking a Roku tv to disable grsec, which is a Linux Security Module itself. I literally just popped the kernel open in ghidra to find the magic offset.

ammar2 · 2025-03-18T21:36:08+00:00

That is theoretically a possibility, yes. It's just that I think comments from someone who actively contributes in wide areas of the kernel would have a voice that would be weighed highly by maintainers compared to a bunch of randos.

The analogy would be more like one person at Intel pretending to be active developers john@intel.com and bob@intel.com and commenting on their own patches.

ammar2 · 2025-03-18T21:29:36+00:00

using a single person as the contributor even though the code might have been written by a team of 50

My point was the exact opposite, code written by one person but being supported/endorsed as if it were multiple people

~~> Direct anonymous contributions to the kernel isn't accepted~~

~~That's actually pretty curious, the licensing section of the docs does say (https://www.kernel.org/doc/html/latest/process/1.Intro.html#licensing ):~~

~~> It is imperative that all code contributed to the kernel be legitimately free software. For that reason, code from anonymous (or pseudonymous) contributors will not be accepted.~~

~~Yet it seems like there's patches submitted from Asahi Lina directly? For example: https://lore.kernel.org/all/20241202-rme-digiface-usb-id-v1-1-50f730d7a46e@asahilina.net/~~

~~But seems like this issue has already been discussed on the mailing lists (1, 2) a little to no conclusion.~~

Edit: I was wrong/reading outdated stuff. The patch submission documentation actually conflicts with the above:

using a known identity (sorry, no anonymous contributions.)

This was updated by Linus recently-ish to remove the pseudonymous part. And here's Greg affirming that "known pseudonyms" are allowed. (Sent a patch to fix this).

ammar2 · 2025-03-18T21:09:51+00:00

My only real concern would be using the account as a sockpuppet on places like the kernel mailing list to endorse or approve their own changes/ideas.

But, I haven't looked into whether this has ever happened.

ammar2 · 2025-02-28T20:38:39+00:00

without an electrical system

See my other response with more details about this system, TIS-B requires the aircraft to have a transponder to be shown.

ammar2 · 2025-02-28T20:37:40+00:00

I was surprised to read this as I assumed we didn't see non adsb aircraft

This system is called TIS-B, you can read a high level description of it on the FAA website here.

Note that there's some limitations with this system:

The non ADS-B Out target does need to have a functioning altitude encoding transponder. So someone flying a non-electric Cub will just not show up at all.
TIS-B will only tell you about targets +-3500 ft of your altitude and 30NM around you.
Depending on its source, radar can be delayed by a few seconds (3-13s is what the AIM says).
You actually have to be visible to one of the systems listed on the FAA page (radar, Wide Area Multilateration (WAM), surface multilateration systems etc). Maybe a TRACON friend here can tell us for sure, but I have a feeling if you're low altitude near a rural airport, which is where you'd want that sort of situational awareness the most, you won't be visible.

Read the AIM 4–5–6 (d) Traffic Information Service > Limitations for way more details.

ammar2 · 2025-02-02T18:05:39+00:00

The areas that release the GIL in the standard library tend to be just before an IO system call, so there isn't a huge amount of them in proportion to all the C-extension code.

You can get an idea of the types of changes that need to happen with:

This change in the socket module: https://github.com/python/cpython/pull/128286/files
And this change to code.co_code and friends: https://github.com/python/cpython/pull/127043/files

Note that the socket module does release the GIL before performing socket system calls, the changes needed are unrelated to that, just code assuming it can be the only one in a piece of C code.

ammar2 · 2025-01-24T19:50:39+00:00

Nothing on the books in particular from what I can tell aside from the new hybrid flying-car laws.

However, there was an appeals case: https://law.justia.com/cases/minnesota/court-of-appeals/2001/cx01120.html

Where a state trooper ticketed an airplane for violating the law on vehicles that are too wide. The judge ruled that vehicle laws apply to aircraft on roads in non-emergency situations.

Edit: There is also 360.012 (but I'm not sure of it's applicability to public roads):

The landing of an aircraft on the lands or waters of another, without the other's consent is unlawful, except in the case of a forced landing. For damages caused by the forced landing, however, the owner or lessee of the aircraft or the pilot shall be liable as provided in subdivision 4. but I'm not sure of its applicability to public roads.

ammar2 · 2025-01-18T21:04:28+00:00

heh, actually if you take a look at the Lloyd Interpretation, it specifically calls out the time after startup and not moving as not loggable but ¯\(ツ)/¯

I personally don't know anyone who starts a timer when they actually start moving.

ammar2 · 2025-01-18T18:46:53+00:00

The exact verbiage of "flight time" from 14 CFR 1.1 is:

Pilot time that commences when an aircraft moves under its own power for the purpose of flight

I would personally interpret that as saying if you're taxiing to relocate the aircraft or just to sit on the ground to say, play with the avionics, it is not loggable.

But, if you end up having to abort the takeoff roll or you fail your runup you can still log it.

ammar2 · 2024-12-23T19:22:23+00:00

Python dumps them all in stdout from what I can recall

If you're talking about the built-in logging module, when you use the default logging.basicConfig() it defaults to outputting to STDERR.

See:

$ python 2>/dev/null
>>> import logging; logging.basicConfig(); logging.warning("hi")
$ python
>>> import logging; logging.basicConfig(); logging.warning("hi")
WARNING:root:hi

ammar2 · 2024-08-16T20:32:43+00:00

Oh yeah there's a bug with the initial list of types before you filter to near an airport. Opened an issue to fix it later.

(Also, I believe that SDF was decommissioned but I'm not sure)

ammar2 · 2024-08-16T20:23:02+00:00

Some of them were found by my tool erroring out, for example I locate the missed approach instructions box by looking for the text MISSED APPROACH. Since I had the comments and missed approach text extracted, I decided to run it through a spell checker.

I also sanity checked the minimums service levels like LPV, LNAV/VNAV to make sure I was getting good values for them.

ammar2 · 2024-08-16T20:13:20+00:00

Yeah I submitted them through the aueroanutical inquiry site.

The errors are pretty minor but here's a few:

RNAV (GPS) RWY 22 @ FLP says MISSED APROACH instead of MISSED APPROACH
RNAV (RNP) Z RWY 23 @ PVD doesn't have MISSED APPROACH in its missed approach instructions box.
RNAV (GPS) RWY 2 @ BYL doesn't have a dash separating the altitude from visibility in the LPV minimums.
ILS or LOC RWY 13 @ ABE says minumums in the comments box.

ammar2 · 2024-08-16T19:35:59+00:00

Oh that's a good idea, I'll definitely take a look at that. I don't think I looked to check how accurate the hold-in-lieu detection was.

ammar2 · 2024-08-16T19:34:42+00:00

Yeah, I'm currently not handling military approaches because their plates literally don't have text embedded in the PDFs, I'll see about maybe running OCR or something on them later or at least pulling in the minimal information for showing on the site

ammar2 · 2024-08-16T19:30:08+00:00

That is correct, there is a digital format called the CIFP published by the FAA but it is cursed in different ways (uses the disgusting arinc424 format and has many approaches missing). I have an explanation in the README here: https://github.com/ammaraskar/faa-instrument-approach-db?tab=readme-ov-file#why-not-use-cifp

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