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Shutting Down Clear Linux OS

https://community.clearlinux.org/t/all-good-things-come-to-an-end-shutting-down-clear-linux-os/10716
24•todsacerdoti•37m ago•3 comments

Asynchrony is not concurrency

https://kristoff.it/blog/asynchrony-is-not-concurrency/
152•kristoff_it•5h ago•104 comments

How to write Rust in the Linux kernel: part 3

https://lwn.net/SubscriberLink/1026694/3413f4b43c862629/
29•chmaynard•1h ago•0 comments

Ccusage: A CLI tool for analyzing Claude Code usage from local JSONL files

https://github.com/ryoppippi/ccusage
14•kristianp•59m ago•4 comments

Silence Is a Commons by Ivan Illich (1983)

http://www.davidtinapple.com/illich/1983_silence_commons.html
60•entaloneralie•3h ago•10 comments

Broadcom to discontinue free Bitnami Helm charts

https://github.com/bitnami/charts/issues/35164
83•mmoogle•4h ago•47 comments

Wii U SDBoot1 Exploit “paid the beak”

https://consolebytes.com/wii-u-sdboot1-exploit-paid-the-beak/
64•sjuut•3h ago•7 comments

lsr: ls with io_uring

https://rockorager.dev/log/lsr-ls-but-with-io-uring/
292•mpweiher•11h ago•151 comments

Multiplatform Matrix Multiplication Kernels

https://burn.dev/blog/sota-multiplatform-matmul/
45•homarp•4h ago•16 comments

EPA says it will eliminate its scientific reseach arm

https://www.nytimes.com/2025/07/18/climate/epa-firings-scientific-research.html
66•anigbrowl•1h ago•35 comments

Valve confirms credit card companies pressured it to delist certain adult games

https://www.pcgamer.com/software/platforms/valve-confirms-credit-card-companies-pressured-it-to-delist-certain-adult-games-from-steam/
145•freedomben•8h ago•147 comments

Meta says it wont sign Europe AI agreement, calling it growth stunting overreach

https://www.cnbc.com/2025/07/18/meta-europe-ai-code.html
85•rntn•6h ago•119 comments

Trying Guix: A Nixer's impressions

https://tazj.in/blog/trying-guix
132•todsacerdoti•3d ago•38 comments

AI capex is so big that it's affecting economic statistics

https://paulkedrosky.com/honey-ai-capex-ate-the-economy/
182•throw0101c•4h ago•202 comments

Replication of Quantum Factorisation Records with a VIC-20, an Abacus, and a Dog

https://eprint.iacr.org/2025/1237
58•teddyh•5h ago•16 comments

Show HN: Molab, a cloud-hosted Marimo notebook workspace

https://molab.marimo.io/notebooks
63•akshayka•5h ago•8 comments

Mango Health (YC W24) Is Hiring

https://www.ycombinator.com/companies/mango-health/jobs/3bjIHus-founding-engineer
1•zachgitt•5h ago

Sage: An atomic bomb kicked off the biggest computing project in history

https://www.ibm.com/history/sage
13•rawgabbit•3d ago•0 comments

The year of peak might and magic

https://www.filfre.net/2025/07/the-year-of-peak-might-and-magic/
69•cybersoyuz•7h ago•36 comments

Show HN: I built library management app for those who outgrew spreadsheets

https://www.librari.io/
44•hmkoyan•4h ago•27 comments

CP/M creator Gary Kildall's memoirs released as free download

https://spectrum.ieee.org/cpm-creator-gary-kildalls-memoirs-released-as-free-download
226•rbanffy•13h ago•118 comments

Cancer DNA is detectable in blood years before diagnosis

https://www.sciencenews.org/article/cancer-tumor-dna-blood-test-screening
153•bookofjoe•5h ago•96 comments

A New Geometry for Einstein's Theory of Relativity

https://www.quantamagazine.org/a-new-geometry-for-einsteins-theory-of-relativity-20250716/
73•jandrewrogers•9h ago•1 comments

Making a StringBuffer in C, and questioning my sanity

https://briandouglas.ie/string-buffer-c/
27•coneonthefloor•3d ago•15 comments

How I keep up with AI progress

https://blog.nilenso.com/blog/2025/06/23/how-i-keep-up-with-ai-progress/
167•itzlambda•5h ago•85 comments

Show HN: Simulating autonomous drone formations

https://github.com/sushrut141/ketu
12•wanderinglight•3d ago•2 comments

Benben: An audio player for the terminal, written in Common Lisp

https://chiselapp.com/user/MistressRemilia/repository/benben/home
46•trocado•4d ago•4 comments

Hundred Rabbits – Low-tech living while sailing the world

https://100r.co/site/home.html
215•0xCaponte•4d ago•60 comments

How to Get Foreign Keys Horribly Wrong

https://hakibenita.com/django-foreign-keys
50•Bogdanp•3d ago•23 comments

When root meets immutable: OpenBSD chflags vs. log tampering

https://rsadowski.de/posts/2025/openbsd-immutable-system-logs/
126•todsacerdoti•15h ago•41 comments
Open in hackernews

Writing a Self-Mutating x86_64 C Program (2013)

https://ephemeral.cx/2013/12/writing-a-self-mutating-x86_64-c-program/
118•kepler471•1mo ago

Comments

belter•1mo ago
I guess in OpenBSD because of W ^ X this would not work?
akdas•1mo ago
I was thinking the same thing. Usually, you'd want to write the new code to a page that you mark as read and write, then switch that page to read and execute. This becomes tricky if the code that's doing the modifying is in the same page as the code being modified.
timewizard•1mo ago
The way it's coded it wouldn't; however, you can map the same shared memory twice. Once with R|W and a second time with R|X. Then you can write into one region and execute out of it's mirrored mapping.
rkeene2•1mo ago
In Linux it also needs mprotect() to change the permissions on the page so it can write it. The OpenBSD man page[0] indicate that it supports this as well, though notes that not all implementations are guaranteed to allow it, but my guess is it would generally work.

[0] https://man.openbsd.org/mprotect.2

Retr0id•1mo ago
It's not required on linux, if the ELF headers are set up such that the page is mapped rwx to begin with. (but rwx mappings are generally frowned upon from a security perspective)
mananaysiempre•1mo ago
Not as is, but I think OpenBSD permits you to map the same memory twice, once as W and once as X (which would be a reasonable hoop to jump through for JITs etc., except there’s no portable way to do it). ARM64 MacOS doesn’t even permit that, and you need to use OS-specific incantations[1] that essentially prohibit two JITs coexisting in the same process.

[1] https://developer.apple.com/documentation/apple-silicon/port...

saagarjha•1mo ago
No, the protection is per-thread. You can run the JITs in different threads
alcover•1mo ago
I often think this could maybe allow fantastic runtime optimisations. I realise this would be hardly debuggable but still..
Retr0id•1mo ago
It already does, in the form of JIT compilation.
alcover•1mo ago
OK but I meant in already native code, like in a C program - no bytecode.
Retr0id•1mo ago
I mean that, too.
connicpu•1mo ago
LuaJIT has a wonderful dynamic code generation system in the form of the DynASM[1] library. You can use it separately from LuaJIT for dynamic runtime code generation to create machine code optimized for a particular problem.

[1]: https://luajit.org/dynasm.html

lmm•1mo ago
If you are generating or modifying code at runtime then how is that different from bytecode? Standardised bytecodes and JITs are just an organised way of doing the same thing.
vbezhenar•1mo ago
I used GNU lightning library once for such optimisation. I think it was ICFPC 2006 task. I had to write an interpreter for virtual machine. Naive approach worked but was slow, so I decided to speed it up a bit using JIT. It wasn't a 100% JIT, I think I just implemented it for loops but it was enough to tremendously speed it up.
userbinator•1mo ago
Programs from the 80s-90s are likely to have such tricks. I have done something similar to "hardcode" semi-constants like frame sizes and quantisers in critical loops related to audio and video decompression, and the performance gain is indeed measurable.
alcover•1mo ago
> "hardcode" semi-constants

You mean you somehow avoided a load. But what if the constant was already placed in a register ? Also how could you pinpoint the reference to your constant in the machine code ? I'm quite profane about all this.

ronsor•1mo ago
> Also how could you pinpoint the reference to your constant in the machine code?

Not OP, but often one uses an easily identifiable dummy pattern like 0xC0DECA57 or 0xDEADBEEF which can be substituted without also messing up the machine code.

mananaysiempre•1mo ago
If you’re willing to parse object files (a much easier proposition for ELF than for just about anything else), another option is to have the source code mention the constants as addresses of external symbols, then parse the relocations in the compiled object. Unfortunately, I’ve been unable to figure out a reliable recipe to get a C compiler to emit absolute relocations in position-independent code, even after restricting myself to GCC and Clang for x86 Linux; in some configurations it works and in others you (rather pointlessly) get a PC-relative one followed by an add.
userbinator•1mo ago
All the registers were already taken.

You use a label.

econ•1mo ago
The 80's:

Say you set a value for some reason. Later you have to check IF it is set. If the condition needs to be checked many times you replace it with the code (rather than set a value to check some place). If you need to check if something is still true repeatedly you replace the condition check with no-ops when it isn't true.

Also funny are insanely large loop unrolls with hard coded valued. You could make a kind of rainbow table of those.

barchar•1mo ago
It sometimes can, but you then have to balance the time spent optimizing against the time spent actually doing whatever you were optimizing.

Also on modern chips you must wait quite a number of cycles before executing modified code or endure a catastrophic performance hit. This is ok for loops and stuff, but makes a lot of the really clever stuff pointless.

The debuggers software breakpoints _are_ self-modifying code :)

112233•1mo ago
Linux kernel had the same idea, and now they have "static keys". It's both impressive and terrifying.
oxcabe•1mo ago
It's impressive how well laid out the content in this article is. The spacing, tables, and code segments all look pristine to me, which is especially helpful given how dense and technical the content is.
AStonesThrow•1mo ago
It was designed by Elves on Christmas Island where Dwarves run the servers and Hobbits operate the power plant
f1shy•1mo ago
I have the suspicion that there is a high correlation between how organized the content is, and how organized and clear the mind of the writer is.
ivanjermakov•1mo ago
I had a great experience writing self modified programs is a single instruction programming game SIC-1: https://store.steampowered.com/app/2124440/SIC1/
ycombinatrix•1mo ago
Cool recommendation, will give it a try.
Someone•1mo ago
Fun article, but the resulting code is extremely brittle:

- assumes x86_64

- makes the invalid assumption that functions get compiled into a contiguous range of bytes (I’m not aware of any compiler that violates that, but especially with profile-guided optimization or compilers that try to minimize program size, that may not be true, and there is nothing in the standard that guarantees it)

- assumes (as the article acknowledges) that “to determine the length of foo(), we added an empty function, bar(), that immediately follows foo(). By subtracting the address of bar() from foo() we can determine the length in bytes of foo().”. Even simple “all functions align at cache lines” slightly violates that, and I can see a compiler or a linker move the otherwise unused bar away from foo for various reasons.

- makes assumptions about the OS it is running on.

- makes assumptions about the instructions that its source code gets compiled into. For example, in the original example, a sufficiently smart compiler could compile

  void foo(void) {
    int i=0;
    i++;
    printf("i: %d\n", i);
  }
as

  void foo(void) {
    printf("1\n");
  }
or maybe even

  void foo(void) {
    puts("1");
  }
Changing compiler flags can already break this program.

Also, why does this example work without flushing the instruction cache after modifying the code?

nekitamo•1mo ago
For the mainstream OSes (Windows, OSX, Linux Android) You don't need to flush the instruction cache on most x86 CPUs after modifying the code segment dynamically, but you do on ARM and MIPS.

This has burned me before while writing a binary packer for Android.

saagarjha•1mo ago
They check all those assumptions by disassembling the code.
Cloudef•1mo ago
> self-modifying code > brittle

I mean that is to be very much expected, unless someone comes up with a programming language that fully embraces the concept.

znpy•1mo ago
The author clearly explained that the whole article is more a demonstration for illustrative purposes than anything else.

> Changing compiler flags can already break this program.

That's not the point of the article.

xixixao•1mo ago
I’ve been thinking a lot about this topic lately, even studying how executables look on arm macOS. My motivation was exploring truly fast incremental compilation for native code.

The only way to do this now on macOS is remapping whole pages as JIT. This makes it quite a challenge but still it might work…

Cloudef•1mo ago
Kaze Emanuar's "Optimizing with Bad Code" video also goes briefly go through self-modifying code https://www.youtube.com/watch?v=4LiP39gJuqE
pfdietz•1mo ago
A program that can generate, compile, and execute new code is nothing special in the Common Lisp world. One can build lambda expressions, invoke the compile function on them, and call the resulting compiled functions. One can even assign these functions to the symbol-function slot of symbols, allowing them to be called from pre-existing code that had been making calls to that function named by that symbol.
BenjiWiebe•1mo ago
I know that no other language can match Lisp, but many languages can generate and execute new code, if they're interpreted. Compile, too, if they're JITted. They all require quite a bit of runtime support though.
DrZhvago•1mo ago
Someone correct me if I am wrong, but self-mutating code is not as uncommon as the author portrays it. I thought the whole idea of hotspot optimization in a compiler is essentially self-mutating code.

Also, I spent a moderately successful internship at Microsoft working on dynamic assemblies. I never got deep enough into that to fully understand when and how customers where actually using it.

https://learn.microsoft.com/en-us/dotnet/fundamentals/reflec...

iamcreasy•1mo ago
Is it possible to mutate the text segment by another process? For example, injecting something malicious instead of exec-ing a shell?