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fuhsnn
slimcc
C2024–2026
fuhsnn / slimcc

slimcc

C23 compiler with C2y/GNU extensions for x86-64 Linux/BSD, written in C99

Systems & InfrastructureLanguages & Compilers
Explore on GitHubRead Hacker News discussions
3Distinct people
10Mentions
0Explicit recommenders
341GitHub stars
REPOSITORY AT A GLANCE

What to know before exploring

What it is

C23 compiler with C2y/GNU extensions for x86-64 Linux/BSD, written in C99

GitHub

Where it is used

No documented product use has been verified yet.

What people are saying

No recommendation phrase was found in the indexed comments.

No classified warning is attached to this page. Read the discussions before treating silence as approval.

Also in these discussions

Mentioned in the same Hacker News threads. That is not proof they are substitutes.

This week on Hacker News

Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 3:56:07 PM UTC.

No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.

Mentions over time

HN mentions by month10 dated mentions

Observed mentions: 2024-08-19 19:25:35 UTC to 2026-10-18 18:49:08 UTC.

01232024-08-01 00:00:00 UTC to 2024-09-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 commentsAug 20242024-09-01 00:00:00 UTC to 2024-10-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2024-10-01 00:00:00 UTC to 2024-11-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2024-11-01 00:00:00 UTC to 2024-12-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2024-12-01 00:00:00 UTC to 2025-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-01-01 00:00:00 UTC to 2025-02-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-02-01 00:00:00 UTC to 2025-03-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-03-01 00:00:00 UTC to 2025-04-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments2025-04-01 00:00:00 UTC to 2025-05-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments2025-05-01 00:00:00 UTC to 2025-06-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-06-01 00:00:00 UTC to 2025-07-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-07-01 00:00:00 UTC to 2025-08-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2025-08-01 00:00:00 UTC to 2025-09-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments2025-09-01 00:00:00 UTC to 2025-10-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 commentsSep 20252025-10-01 00:00:00 UTC to 2025-11-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments2025-11-01 00:00:00 UTC to 2025-12-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 comments2025-12-01 00:00:00 UTC to 2026-01-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-01-01 00:00:00 UTC to 2026-02-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-02-01 00:00:00 UTC to 2026-03-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-03-01 00:00:00 UTC to 2026-04-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-04-01 00:00:00 UTC to 2026-05-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-05-01 00:00:00 UTC to 2026-06-01 00:00:00 UTC (exclusive): 3 mentions; 1 submissions, 2 comments2026-06-01 00:00:00 UTC to 2026-07-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-07-01 00:00:00 UTC to 2026-08-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-08-01 00:00:00 UTC to 2026-09-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-09-01 00:00:00 UTC to 2026-10-01 00:00:00 UTC (exclusive): 0 mentions; 0 submissions, 0 comments2026-10-01 00:00:00 UTC to 2026-11-01 00:00:00 UTC (exclusive): 1 mentions; 0 submissions, 1 commentsOct 2026

Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.

View mention counts and date ranges
UTC ranges include their start and exclude their end. Select a period to filter the source evidence.
PeriodStart (UTC)End (exclusive, UTC)MentionsSubmissionsComments
Aug 20242024-08-01 00:00:00 UTC2024-09-01 00:00:00 UTC101
Sep 20242024-09-01 00:00:00 UTC2024-10-01 00:00:00 UTC000
Oct 20242024-10-01 00:00:00 UTC2024-11-01 00:00:00 UTC000
Nov 20242024-11-01 00:00:00 UTC2024-12-01 00:00:00 UTC000
Dec 20242024-12-01 00:00:00 UTC2025-01-01 00:00:00 UTC000
Jan 20252025-01-01 00:00:00 UTC2025-02-01 00:00:00 UTC000
Feb 20252025-02-01 00:00:00 UTC2025-03-01 00:00:00 UTC000
Mar 20252025-03-01 00:00:00 UTC2025-04-01 00:00:00 UTC101
Apr 20252025-04-01 00:00:00 UTC2025-05-01 00:00:00 UTC101
May 20252025-05-01 00:00:00 UTC2025-06-01 00:00:00 UTC000
Jun 20252025-06-01 00:00:00 UTC2025-07-01 00:00:00 UTC000
Jul 20252025-07-01 00:00:00 UTC2025-08-01 00:00:00 UTC000
Aug 20252025-08-01 00:00:00 UTC2025-09-01 00:00:00 UTC101
Sep 20252025-09-01 00:00:00 UTC2025-10-01 00:00:00 UTC000
Oct 20252025-10-01 00:00:00 UTC2025-11-01 00:00:00 UTC101
Nov 20252025-11-01 00:00:00 UTC2025-12-01 00:00:00 UTC101
Dec 20252025-12-01 00:00:00 UTC2026-01-01 00:00:00 UTC000
Jan 20262026-01-01 00:00:00 UTC2026-02-01 00:00:00 UTC000
Feb 20262026-02-01 00:00:00 UTC2026-03-01 00:00:00 UTC000
Mar 20262026-03-01 00:00:00 UTC2026-04-01 00:00:00 UTC000
Apr 20262026-04-01 00:00:00 UTC2026-05-01 00:00:00 UTC000
May 20262026-05-01 00:00:00 UTC2026-06-01 00:00:00 UTC312
Jun 20262026-06-01 00:00:00 UTC2026-07-01 00:00:00 UTC000
Jul 20262026-07-01 00:00:00 UTC2026-08-01 00:00:00 UTC000
Aug 20262026-08-01 00:00:00 UTC2026-09-01 00:00:00 UTC000
Sep 20262026-09-01 00:00:00 UTC2026-10-01 00:00:00 UTC000
Oct 20262026-10-01 00:00:00 UTC2026-11-01 00:00:00 UTC101

What Hacker News says

10 sources
fuhsnn·Oct 18, 2026
There was a "__VA_TAIL__" WG14 proposal[1] that made it pretty simple to build custom map-like expansions, the OP's map example would be like: > #define T(x, ...) printf(#x " = %d\n", x); __VA_TAIL__() > T(1, 2, 3, 4, x, y, z) You can play with it in the proposal author's ellipsis[2] and my slimcc[3], it's simple enough to implement (only about 30 lines of C) so I kept it in despite not seeing signs of it getting accepted. [1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3307.htm [2] https://codeberg.org/gustedt/ellipsis [3] https://github.com/fuhsnn/slimcc
In Fun Extending the C Preprocessor
fuhsnn·May 25, 2026
For those who are making indie C compilers that don't pretend to be __GNUC__ but want to compile real world projects, slimcc's test script[1] and platform header hacks[2] might save you some time. [1] https://github.com/fuhsnn/slimcc/blob/main/scripts/linux_thi... [2] https://github.com/fuhsnn/slimcc/blob/main/slimcc_headers/pl... Some more fun stories: - Game projects default to using SIMD so for example SDL and STB you always need to pass -DSDL_DISABLE_IMMINTRIN_H and -DSTB_NO_SIMD - math.h's NAN usually fall back to (0.0f / 0.0f), which will print "-nan" with printf, some projects test suite fail because of it (they expected "nan"). - NetBSD's sys/cdefs.h straight up #error's if you don't pretend to be GCC or PCC. - Some projects can't compile without __attribute__((always_inline)) because they use it on non-static functions. - Many pr
Read the rest
ojects probe -fvisibility in the build system and pass -fvisibility=hidden to compile, but in the headers they gate __attribute__((visibility(default))) behind __GNUC__ checks, so you'll get missing symbols. - Some projects use if(0) { undefined_function() } to fake static_assert(), there is even a bug report from QEMU to Clang because it failed to optimize in -O0 a certain `if` written this way. - Even if you define __STDC_NO_VLA__, projects might fall back to alloca() code path that's untested and broken (python and jemalloc both had this problem, already reported) - Valkey has broken __builtin_ctzll fallback nobody noticed (reported). - Zig's C bootstrap path expects the compiler to have GCC/Clang-tier optimization and stack overflows if you don't (reported). - I contributed stdatomic.h code path for Ruby just to compile it with slimcc, pretty sure it's still the only user of the code path. - I implemented __has_extension in the hope that projects can use it to query gnu_asm; but SQLite broke because they use __has_extension(c_atomic) to query GNU atomics builtin, but c_atomic actually is meant for C11 _Atomic (IMO they should use __has_builtin)
In C extensions, portability, and alternative compilers
fuhsnn·Aug 17, 2025
Thanks for the tips! Yes it can always be worked around, however the intuition I developed from doing it for over a hundred of projects [1] is that, with script like that there usually would be more compiler assumptions in C code as well, then I just move on to other projects. (And it also feels awkward whether to report portability issues to projects with such script because it's like a clear "not for other compilers" message, similar to projects that adopted Meson) [1] https://github.com/fuhsnn/slimcc/blob/94dde1b8080e02b188ea89...
In Comparison of different C libraries providing generic containers capabilities
fuhsnn·Apr 22, 2025
It's great of programmers to aim for portability, but frankly it's kind of a stretch that an arbitrary C compiler that is limited in standard support would the same time be sophisticated enough to process these tricks as intended. In my fork of chibicc (a small C11 compiler) there are plenty of additional logic that were implemented solely to play nice with C tricks from real world projects that could have been easier if they target later standards. The most recent being how curl's build script determines the size of primitive types: they use (sizeof(T) == N) as a case index and expect the compiler to error on case-duplication[1], I had to add a backtracking loop to check exactly that[2]. I'm not complaining as more error checks isn't a bad thing, however, I'll advise programmers willing to invest in obscure tricks to actually test them o
Read the rest
n obscure compilers (instead of just flipping -std). [1]: https://github.com/curl/curl/blob/339464432555b9bd71a5e4a4c4... [2]: https://github.com/fuhsnn/slimcc/blob/54563ecae8480f836a0bb2...
In Detecting if an expression is constant in C
fuhsnn·Aug 19, 2024
>[[musttail]] also ends the lifetime of local objects AFAICS. That's good to know. I had this github issue [0] in the back of my mind, as well as witnessing occasions of clang turning [[musttail]] into inner loops, and concluded clang's implementation must be more sophisticated than simply replacing calls with jumps. Just a little paranoia from trying to be serious with compiler dev[1]: fulfilling a laid-out spec feels more sound versus imitating something out there. >this constraint is unnecessarily strict I would agree, at least for x86 psABI, it can be pretty elaborative as long as the return value is the same register and argument stack don't exceed what's provided. Debug/profiling side might hate it, though. [0] https://github.com/llvm/llvm-project/issues/72555 [1] https://github.com/fuhsnn/slimcc/
In Parsing protobuf at 2+GB/s: how I learned to love tail calls in C (2021)

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