pbrowne011

3 か月前議論

Feels like this would be a good candidate for Pike's programming rules (https://www.cs.unc.edu/~stotts/COMP590-059-f24/robsrules.htm...):

"Rule 1. You can't tell where a program is going to spend its time. Bottlenecks occur in surprising places, so don't try to second guess and put in a speed hack until you've proven that's where the bottleneck is.

Rule 2. Measure. Don't tune for speed until you've measured, and even then don't unless one part of the code overwhelms the rest."

pbrowne011

3 か月前議論

Very cool! TIL about Ghostscript: https://ghostscript.com/about/index.html

Awesome to see someone continuing in the tradition of free/libre OSS: https://linuxclass.heinz.cmu.edu/doc/Open-Source-books/Free-...

pbrowne011

3 か月前議論

Interesting to see how their CLI compares with GitLab's CLI interface for stacked diffs (the only support they offer at the moment): https://docs.gitlab.com/user/project/merge_requests/stacked_.... Most things are the same (up/down/top/bottom vs. next/prev/first/last, init vs. create), but both feel quite limiting. I've heard of other systems such as Gerrit that offer better native support, but have not tried out any for myself.

pbrowne011

昨年議論

If you'd like to read something that is less detailed, I4R (Institute for Replication) posted threads on X (formerly known as Twitter) and Bluesky about their investigation into this paper.

X (Twitter): https://x.com/I4Replication/status/1893842119594258913

Bluesky: https://bsky.app/profile/i4replication.bsky.social/post/3liv...

pbrowne011

昨年議論

It seems crazy to me that vulnerabilities like this still exist today. I understand that not everything will be written in Rust, but this could have been caught by basic testing and/or fuzzing, as Nick (the person who found the vulnerability) points out: https://www.openwall.com/lists/musl/2025/02/14/1. So far, this earned an 8.1 from MITRE: https://nvd.nist.gov/vuln/detail/CVE-2025-26519, although I'm not sure if that's just a function of it being a bug in a library that so many applications use.

This also goes to show how every line matters. The one line change was from

    if (c >= 93 || c>=0xc6-0x81 && d>0x52)

    if (c > 0xc6-0x81 || c==0xc6-0x81 && d>0x52)

Link to relevant source code: https://git.musl-libc.org/cgit/musl/tree/src/locale/iconv.c (bug fix is line 505).

To explain the bug, EUC_KR is Extended Unicode - Korean. After ASCII characters (0-127), each character is multiple bytes. The logic adjusts to look up from a base-0 index, then checks that both bytes (variables c and d) are in the normalized range. If not, the code adjusts the characters and checks the bounds again. This second check is what contained the bug.

0xc6 - 0x81 is the upper bound of this check (69), not 93. The irony is that the second part of the check gets this correct. I wonder what a `git blame` would reveal about this particular line.

pbrowne011

昨年議論

Fun to see someone decide to just write a faster JSON parser because they believed it was possible. They mentioned last year that libjansson had some intermediate layer with Emacs, which led to too many memory allocations: https://lists.gnu.org/archive/html/emacs-devel/2024-03/msg00...

Also, the developer who wrote the parser (Géza Herman) was able to pass all of the tests with strange edge cases from https://seriot.ch/projects/parsing_json.html very quickly: https://lists.gnu.org/archive/html/emacs-devel/2024-03/msg00...

pbrowne011

昨年議論

True, I was trying to find the variable storage requirements in the UEFI specification but couldn't (is it Section 3? 8?), so I resorted to linking to the struct definition in the EFI shell package that the author used.

pbrowne011

昨年議論

Very interesting. I wonder if this a result of some "swiss cheese" effect due to constraints around UEFI and NVRAM themselves, when updating EFI variables.

NVRAM must maintain atomicity of memory transactions for power failures. Its whole purpose is to store data when you turn your computer off. As a result, when deleteing an EFI variable, you can't manage the individual bytes - you have to delete a whole entry (which can be rather large - based on the EFI specification and the code used for edk2, e.g. https://github.com/tianocore/edk2/blob/83a86f465ccb1a792f5c5...). Deleting these entries might become a problem when you start running against memory constraints and what slots in memory are actually available; hence a possible fragmentation issue.

Additionally, I appreciated how short and specific this blog post was. I enjoy this style of post of someone encountering a problem and solving it.

pbrowne011

2 年前議論

While this didn't get much attention on History Stack Exchange, see ConeOfArc's YouTube video (which has 963k views as of today): https://www.youtube.com/watch?v=HaRO_dTqO1E

See also ConeOfArc's video from a month later, https://www.youtube.com/watch?v=RO58B6LcTfM (1M views). The video above is about the initial search and problem, this video is after many Internet strangers worked together to solve it.

pbrowne011

2 年前議論

"The more skilled you are, the less you need advanced tools..."

I wonder how well this claim holds up under strict scrutiny. At a high level, it makes sense: someone who is a master of their craft will understand their tools and how to use them much better than a beginner starting out. However, I think this is a different claim than the one Paolini makes.

One concrete argument against this is the history of technological progress. With each improvement came a step function in the tools available to builders, creators, etc., and those able to master them achieved a new level of ability and progress not seen before.

There is evidence for this everywhere. In sports, athletes today use modern technologies and knowledge to push their bodies and abilites to new levels (low-oxygen training, equipment specialized in each sport, etc.). If you didn't upgrade your golf clubs from wood to titanium, you are going to be left far behind. In other industries, this applies: a specific example might be in welding, where using a multi-process welder will significantly improve your productivity as well as the quality of your work. [1]

In tech, this distinction is also apparent. There are the dual cases of a programmer being completely ineffective with a modern IDE versus Jeff Dean (or insert your favorite programming legend here) with Emacs (or another text editor). However, this does not mean that a great programmer does not require advanced tools. Great toolchains (compilers, linkers, interpreters, debuggers, etc.), advanced computing capabilities (GPUs for LLMs), and high-speed Internet access will dramatically change the quality of your work.

I think that Paolini is more focused on the idea that a master craftsmen, when compared with a beginner, can still handily defeat the beginner using simple tools, as they understand both the tools and what they are trying to accomplish better. I agree with this point, but think that this relative comparison is distinct from the absolute comparison of a master using simple tools vs. the same master using advanced tools.

I appreicate his larger point that you want high-quality (even if simple) tools that you understand and that will last you a lifetime. This is one of the main benefits of mastering free/open source software [2]: freedom 0 of free software is to run a program as you wish, for any purpose, which is not guaranteed when using proprietary software.

[1] https://www.constructionequipment.com/light-equipment/weldin...

[2] https://gwern.net/choosing-software

pbrowne011

2 年前議論

Is the main idea to convert the model implementation from Python into C, then hardcode all possible values? Do you do this yourself in the generator code, or could you let the C preprocessor/compiler handle something like this by using macros? (might help with compile time/memory)

"NOTE: Ensure the device you are running on has no form of hardware acceleration like GPU or the results will be skewed"

How much does adding GPUs affect your performance improvement gains? I understand that the point of this optimization is for CPU-only machines, but it would be interesting to consider the affect your optimizations have when running on GPUs as well.

pbrowne011

2 年前議論

From The Register, with more comments by Filip ("Phil") Pizlo (the author): https://www.theregister.com/2024/11/16/rusthaters_unite_filc....

Other memory safe implementations for C and C++ mentioned/proposed are TrapC (https://vimeo.com/1028578347) and Safe C++ (https://safecpp.org/draft.html).

Fil-C adds capabilities and garbage, though it mentions performace costs of 1.5x - 5x. I would think the capabilties aspect of this language extension would be better addressed by hardware proposals (like CHERI) to prevent adding too much overhead to systems that are performance-critical.

Edit: It also looks like the author could use help porting C programs to Fil-C, see https://news.ycombinator.com/item?id=42158296.

pbrowne011

2 年前議論

(2016)

The comments on this fast range reduction are interesting, I recommend reading them (they're much longer than the post itself). Some highlights:

Versions of this exist as early as 1997, in CMU's Common Lisp implementation. Their GitLab is not loading quicky on my computer, but the commit is supposed to be from December by Douglas Crosher (https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-...).

The "Further reading" section (and comments) include implementations of the trick in the wild. Stockfish, the chess engine, used this optimization to reduce memory for storing precomputations of moves in their transposition tables (https://github.com/official-stockfish/Stockfish/commit/2198c...). The commit switches from using bitwise AND (&) and power-of-2 table sizes to using the modulo hash trick, which allows for full use of RAM (even if it's not an exact power of 2). It's also used in Hashtron's modular hash: https://github.com/neurlang/classifier/blob/master/hash/hash..., a straightforward application of the optimization to avoid using modulo.

A GitHub gist with more information: https://github.com/sipa/writeups/tree/main/uniform-range-ext.... It walks through a couple of intuitive explanations on why this technique maintains maximum uniformity in the output distribution, as opposed to the proof in the post.

pbrowne011

2 年前議論

More recent revision: https://isocpp.org/files/papers/P2900R10.pdf. It seems like they've added a few things since this draft.

It's somewhat funny to hear "minimum viable product" in the context of a language standard/specification. I'd never thought of adding a feature to a language in that way before.

The idea of design by contract (DbC) in C++ appears to have been around for a while too. The authors link to a "forthcoming companion paper" (currently a 404 error), but you can find proposals from as early as 2004 with the idea: https://www.open-std.org/JTC1/SC22/WG21/docs/papers/2004/n16...

(and potentially earlier, I just haven't seen one yet)

pbrowne011

2 年前議論

"Classic C++" and "Modern C++" refer to the language before and after C++11, respectively.

Some of the key differences are use of standard library and its containers, smart pointers, and other language features that look less like C. In this specific library, this refers to some of the techniques like bit manipulation, manual memory management and string parsing, and using things like enums to improve speed and reduce complexity.

An example of a more robust (but still "classic") library would be something like https://github.com/Tencent/rapidjson.

pbrowne011

2 年前議論

In embedded systems with hard real-time requirements, there are several ways to schedule tasks. Once the number of tasks you need to execute grows long enough, scheduling becomes a challenge. An RTOS is one way to manage these tasks with guaranteed, deterministic timing.

A concrete example: if you're in a car (an embedded system doing many things at once) and press the brakes, you want the car to be as responsive as possible. A real-time operating system will sacrifice other features of a general purpose OS to guarantee that the brakes are applied within a specified time interval after you press them.

Also, there are responses to a similar comment from when this was previously posted: https://news.ycombinator.com/item?id=32329499

pbrowne011

2 年前議論

I wonder - did the US government, specifically DARPA, consider CHERI when laying out their "Translating All C to Rust (TRACTOR)" initiative? The two initiatives could be compatible (memory safety at both the software and hardware level), especially since CHERI might be more feasible when it comes to rewriting legacy software.

pbrowne011

2 年前議論

Prior thread (with comments): https://news.ycombinator.com/item?id=27046272

pbrowne011

2 年前議論

I had not considered using a VM instead of strace when a program can detect ptrace(2) being used - good idea.

> Normally when reverse engineering a program, it is common to use tracing programs like strace. These tracing programs are quite useful, but they suffer from a design flaw: they use ptrace(2) to accomplish the tracing, which can be detected by the program being traced.

One way to do this would be to call ptrace() from your program and check if it returns the error EPERM. From the man page:

       EPERM  The specified process cannot be traced.  This could be because the tracer has  insufficient  privileges
              (the  required  capability  is CAP_SYS_PTRACE); unprivileged processes cannot trace processes that they
              cannot send signals to or those running set-user-ID/set-group-ID programs, for obvious reasons.  Alter‐
              natively, the process may already be being traced, or (on kernels before 2.6.26) be init(1) (PID 1).

However, this is not the best solution, as if your system has a security policy already in place for ptrace() detection, your process might get detected and killed. Other methods from the calling process might involve timing mechanisms, breakpoint detection, or checking other factors in the process' environment. One problem with the workaround suggested in this post (running a process from qemu-user) is that if it is truly security hardened, it might rely on timing differences smaller than the speed of VM instruction execution.

As a user or sysadmin, one way to detect ptrace is to use Yama [1], a Linux kernel module that creates an entry in /proc/sys/kernel/yama/ptrace_scope to configure a user's desired level of ptrace protection, from 0 (normal - any process can call ptrace() on another process owned by the same user) to 3 (completely disabling ptrace).

[1] https://www.kernel.org/doc/html/latest/admin-guide/LSM/Yama....

pbrowne011

2 年前議論

Another name for a similar but slightly more pernicious problem is the Gell-Mann Amnesia effect: "the phenomenon of experts reading articles within their fields of expertise and finding them to be error-ridden and full of misunderstanding, but seemingly forgetting those experiences when reading articles in the same publications written on topics outside of their fields of expertise, which they believe to be credible."

https://en.wikipedia.org/wiki/Michael_Crichton#Gell-Mann_amn...

pbrowne011

投稿

The European Schuko socket bothers me

A Wrigley Mystery (2024)

How not to Reference Papers (2014)

Reproduction of "Improving Women's Mental Health During a Pandemic"

The Billionaire's Typewriter (2019)

Handling exceptions in Python like a pro (2021)

How to Prove False Statements: Practical Attacks on Fiat-Shamir

There's No Such Thing as Software Productivity (2012)

CRUFT: An alternative to the Technical Debt metaphor

Strong Advice (2021)

How humans write programs (2018)

Making a Tiny E-Paper Status Display for the Raspberry Pi Zero

Understanding Common Factor Attacks: An RSA-Cracking Puzzle

1B Nested Loop Iterations

The Rubaiyat (1120 ACE)

An attempt to backdoor the kernel (2003)

Dabbling in the Cryptographic World–A Story (1999)

The American M-209 cipher machine

It's time for a modern synthesis kernel (2019)

The performance of hashing for similar function detection

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