What is Hackers' Pub?

Hackers' Pub is a place for software engineers to share their knowledge and experience with each other. It's also an ActivityPub-enabled social network, so you can follow your favorite hackers in the fediverse and get their latest posts in your feed.

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Jens Gustedt's Blog @gustedt.wordpress.com@gustedt.wordpress.com
Public
Shared by ✧✦Catherine✦✧

Defer available in gcc and clang

About a year ago I posted about defer and that it would be available for everyone using gcc and/or clang soon. So it is probably time for an update.

Two things have happened in the mean time:

  • A technical specification (TS 25755) edited by JeanHeyd Meneide is now complete and moves through ISO’s complicated publication procedures.
  • Both gcc and clang communities have worked on integrating this feature into their C implementations.

I have not yet got my hands on the gcc implementation (but this is also less urgent, see below), but I have been able to use clang’s which is available starting with clang-22.

I think that with this in mind everybody developing in C could and should now seriously consider switching to defer for their cleanup handling:

  • no more resource leakage or blocked mutexes on rarely used code paths,
  • no more spaghetti code just to cover all possibilities for preliminary exits from functions.

I am not sure if the compiler people are also planning back ports of these features, but with some simple work around and slightly reduced grammar for the defer feature this works for me from gcc-9 onward and for clang-22 onward:

#if __has_include(<stddefer.h>)
# include <stddefer.h>
# if defined(__clang__)
#  if __is_identifier(_Defer)
#   error "clang may need the option -fdefer-ts for the _Defer feature"
#  endif
# endif
#elif __GNUC__ > 8
# define defer _Defer
# define _Defer      _Defer_A(__COUNTER__)
# define _Defer_A(N) _Defer_B(N)
# define _Defer_B(N) _Defer_C(_Defer_func_ ## N, _Defer_var_ ## N)
# define _Defer_C(F, V)                                                 \
  auto void F(int*);                                                    \
  __attribute__((__cleanup__(F), __deprecated__, __unused__))           \
     int V;                                                             \
  __attribute__((__always_inline__, __deprecated__, __unused__))        \
    inline auto void F(__attribute__((__unused__)) int*V)
#else
# error "The _Defer feature seems not available"
#endif

So this is already a large panel of compilers. Obviously it depends on your admissible compile platforms whether or not these are sufficient for you. In any case, with these you may compile for a very wide set of installs since defer does not need any specific software infrastructure or library once the code is compiled.

As already discussed many times, the gcc fallback uses the so-called “nested function” feature which is always subject of intense debate and even flame wars. Don’t worry, the implementation as presented here, even when compiled with no optimization at all, does not produce any hidden function in the executable, and in particular there is no “trampoline” or whatever that would put your execution at risk of a stack exploit.

You may also notice that there is no fallback for older clang version. This is because their so-called “blocks” extension cannot easily be used as a drop-in to replace nested function: their semantics to access variables from the surrounding scope are different and not compatible with the defer feature as defined by TS 25755.

So for example if you are scared of using big VLA on the stack, you may use the above code in headers and something like

double* BigArray
  = malloc(sizeof(double[aLot]));
if (!BigArray {
  exit(EXIT_FALURE);
}
defer { 
  free(BigArray); 
}

to have an implementation of a big array with a failure mode for the allocation.

Or if you want to be sure that all your mutexes are unlocked when you leave a critical section, use and idiom as here

{
  if (mtx_lock(&mtx) != thrd_success) {
    exit(EXIT_FAILURE);
  }
  defer {
    mtx_unlock(&mtx);
  }

  ... do something complicated ...

  if (rareCondition) {
    return 42;
  }

  ... do something even more complicated ...
}

Just notice, that you’d always have to use the defer feature with curly braces to ensure that the gcc fallback works smoothly.

Simple defer, ready to use

With this post I will concentrate on the here and now: how to use C’s future lifesaving defer feature with existing tools and compilers.

gustedt.wordpress.com · Jens Gustedt's Blog

Link author: Jens Gustedt's Blog@gustedt.wordpress.com@gustedt.wordpress.com

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Hacker News 50 @hn50@social.lansky.name
Public

Don't create .gitkeep files, use .gitignore instead (2023)

Link: adamj.eu/tech/2023/09/18/git-d
Discussion: news.ycombinator.com/item?id=4

Git: Don’t create .gitkeep files, use .gitignore instead - Adam Johnson

Git only tracks files, not directories. It will only create a directory if it contains a tracked file. But sometimes you need to “track” a directory, to ensure it exists for fresh clones of a repository. For example, you might need an output directory called build.

adamj.eu

Link author: Adam Johnson :django: :python:@adamchainz@fosstodon.org

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Erin Kissane @kissane.bsky.social@bsky.brid.gy
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Shared by kiding 🧑‍💻 | Dongsung "Donny" Kim

The headline does not convey how completely batshit this story is. The Archive Today (archive.ph etc) admin weaponized the site's captcha to attack a blogger who wrote about them and *altered archived screenshots* as part of the attack. arstechnica.com/tech-policy/...

Wikipedia blacklists Archive.t...

archive.md

archive.md allows you to create a copy of a webpage that will always be up even if the original link is down

archive.md · archive.md

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Eric Florenzano @ericflo@mastodon.xyz
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The whole software factory thing is real and powerful. Lately have been feeling the magnitude of the moment. The opportunity and the challenge of it. Things will be so different even in the next few years. And yet, we will be the same.

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Readmoo讀墨電子書（轉發） @readmoo@mistyreverie.org
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有些人覺得年輕時要努力打拚、盡量存錢，很多事可以等年紀大了、退休之後再做，例如什麼環遊世界啦學畫、學琴啦，反正年輕時你覺得浪費錢浪費時間，但好像很有趣的事，都可以等賺夠了錢再來做。

可是這些人到了年紀大了退休的時候，也常常會抱怨因為年輕時太打拚所以身體變得不大好或頭腦太疲勞，環遊世界學畫學琴什麼的，要嘛沒體力要嘛沒興致要嘛健康狀況不允許。

所以計劃不是不能做，但真該好好計劃的不見得是很具體的某件事──那件事可能在很多因素下忽然變得很容易完成或者失去魅力──真正該做的老年計劃，不見得是要去環遊世界學畫學琴，而是如何一個人好好過日子。

https://moo.ink/8qc9vv
https://moo.ink/8qca39

【一週E書】真該好好計劃的是怎樣才能開心順利地活著：《孤獨才是最棒的晚年》

moo.ink

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cliffle @cliffle@hachyderm.io
Public

Thinking through some PL design questions this evening, and it occurs to me...

There is very little, in practice, here in the year 2026, that prevents me from naming a programming language with an emoji.

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Yappy Yowlidays! - He/Him @sec_yote_agenda@mstdn.party
Public

The Discord situation just keeps getting 'better'.

malwarebytes.com/blog/news/202

Age verification vendor Persona left frontend exposed, researchers say

Behind a basic age check, researchers say Persona’s system runs extensive identity, watchlist, and adverse-media screening.

www.malwarebytes.com · Malwarebytes

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Natasha Jay 🇪🇺 @Natasha_Jay@tech.lgbt
Public
Shared by earthling

NewScientist: "Antibodies harvested from the blood of paediatricians are up to 25 times better at protecting against the common respiratory infection RSV than existing antibody therapies, and are now being developed as preventative treatments"

This is both so logical and yet absurdly like a science fiction story ...

newscientist.com/article/25160

Paediatricians’ blood used to make new treatments for RSV and colds

Antibodies harvested from the blood of paediatricians are up to 25 times better at protecting against the common respiratory infection RSV than existing antibody therapies, and are now being developed as preventative treatments

www.newscientist.com · New Scientist

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Julia Evans @b0rk@jvns.ca
Public
Shared by jnkrtech

out of curiosity, when did you first start using unix systems?

(please no replies with details on this one, if none of them fit exactly that's ok, just trying to get a very rough sense)

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Silverkey | 은열쇠 @silverkey.social@bsky.brid.gy
Public

대법원 맹폭한 트럼프 “국가의 수치들이 내린 판결” 트럼프 대통령은 관세 위헌 판결을 내린 대법관들을 ‘반애국적’이라며 맹비난하는 한편, 1974년 무역법 등을 동원해 10% 추가 보편 관세를 재부과하겠다는 계획을 발표했다.

대법원 맹폭한 트럼프 “국가의 수치들이 내린 판결”

대법원 맹폭한 트럼프 “국가의 수치들이 내린 판결”

Jason Ma & 김다린 기자 · 대법원이 국제긴급경제권한법(IEEPA)을 근거로 한 보편 관세에 위헌 판결을 내리자, 도널드 트럼프 대통령은 즉각 기자회견을 열고 분노를 표출했다. 그는 이번 판결을 ‘애국심 없는 행위’로 규정하며 행정부의 관세 주권을 포기하지 않겠다고 선언했다.트럼프 대통령은 위헌 판결을 내린 6명의 대법관을 향해 “부끄러운 줄 알라”며 “우리나라를 위해 옳은 일을 할 용기가 없다”고 비난했다. 그는 이들을 ‘RINO(무늬만 공화당원)’와 ‘급진 좌파’의 앞잡이라 지칭하며, 심지어 “법원이 외국 이익에 휘둘리고 있다는 것이 내 생각”이라고 주장했

www.fortunekorea.co.kr · 포춘코리아

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은열쇠🥨 :ivory_boost: @Silverkey027@mastodon.social
Public

대법원 맹폭한 트럼프 “국가의 수치들이 내린 판결”

트럼프 대통령은 관세 위헌 판결을 내린 대법관들을 ‘반애국적’이라며 맹비난하는 한편, 1974년 무역법 등을 동원해 10% 추가 보편 관세를 재부과하겠다는 계획을 발표했다. fortunekorea.co.kr/news/articl

대법원 맹폭한 트럼프 “국가의 수치들이 내린 판결”

Jason Ma & 김다린 기자 · 대법원이 국제긴급경제권한법(IEEPA)을 근거로 한 보편 관세에 위헌 판결을 내리자, 도널드 트럼프 대통령은 즉각 기자회견을 열고 분노를 표출했다. 그는 이번 판결을 ‘애국심 없는 행위’로 규정하며 행정부의 관세 주권을 포기하지 않겠다고 선언했다.트럼프 대통령은 위헌 판결을 내린 6명의 대법관을 향해 “부끄러운 줄 알라”며 “우리나라를 위해 옳은 일을 할 용기가 없다”고 비난했다. 그는 이들을 ‘RINO(무늬만 공화당원)’와 ‘급진 좌파’의 앞잡이라 지칭하며, 심지어 “법원이 외국 이익에 휘둘리고 있다는 것이 내 생각”이라고 주장했

www.fortunekorea.co.kr · 포춘코리아

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ballotproof vest @starchy@infosec.exchange
Public
Shared by Paul Cantrell

'A note reading “Hahaha get wrecked ya surveilling fucks” was attached to one of the destroyed poles, and somewhat incredibly, broadcast on the local news.'
bloodinthemachine.com/p/across

Across the US, people are dismantling and destroying Flock surveillance cameras

Anger over ICE connections and privacy violations is fueling the sabotage. PLUS: 10,000 drivers call on Uber to repay stolen wages, a man is arrested at a public hearing about a data center and more.

www.bloodinthemachine.com

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Natasha Jay 🇪🇺 @Natasha_Jay@tech.lgbt
Public
Shared by Paul Cantrell

NewScientist: "Antibodies harvested from the blood of paediatricians are up to 25 times better at protecting against the common respiratory infection RSV than existing antibody therapies, and are now being developed as preventative treatments"

This is both so logical and yet absurdly like a science fiction story ...

newscientist.com/article/25160

Paediatricians’ blood used to make new treatments for RSV and colds

Antibodies harvested from the blood of paediatricians are up to 25 times better at protecting against the common respiratory infection RSV than existing antibody therapies, and are now being developed as preventative treatments

www.newscientist.com · New Scientist

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