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For my first C class in uni I wrote a curses-style CLI spreadsheet tool with a csv parser, reverse cell reference table, automatic modification-based recursive

For my first C class in uni I wrote a curses-style CLI spreadsheet tool with a csv parser, reverse cell reference table, automatic modification-based recursive recalculation, a basic formula parser, an infix notation to reverse polish notation "compiler", and a stack-based RPN evaluator (I may have gone a bit overboard on that assignment). The one multi-user unix server for all students that I wrote it on (named 'foley', some CS reference I think) had an ancient gcc compiler that compiled it just fine, but when run it would segfault. Hardly surprising, I created hundreds of segfaults, but this one would only segfault if I used -O0 and didn't add any logging statements. That's right, it ran fine with any level of optimization above 0 or if I used any logging statements, and only segfaulted on -O0. Utterly infuriating and flagrantly defied my expectations. I got help from some patient soul I found on freenode ##c (I wish I could remember their name) who didn't see any obvious issue or warning and couldn't reproduce any segfault with their much more recent compiler. -Wall+++, asan, nothing cracked it. Everything else was exhausted: it must be the compiler. But I couldn't just update the compiler package because it was a multi-user server and I had zero permissions, so I ended up bootstrapping a 10-years newer gcc through multiple intermediate versions and installing it in my profile (quotas be damned) and used that. It didn't segfault on -O0 anymore. I haven't voluntarily used C since.

kragen 4y ago
That's not related to C, except in the sense that GCC is written in C. GCC was just emitting incorrect code because it had a bug in its code generator. If there's a bug in the LLVM code generator (which is written in C++), rustc might end up doing the same thing. If you write the compiler in Rust it could still happen. Rust code (that compiles) has less bugs than the corresponding C but not zero bugs. It doesn't sound like you went overboard, it sounds like a good project. Maybe you should have written it in Perl 5.001 though.
- charcircuit 4y ago
  GCC is written in C++
  - kragen 4y ago
    There are small parts of GCC that are written in C++, but at the time when universities had "one multi-user unix server for all students" it was 100% C.
    - turminal 4y ago
      and there was no LLVM :)
      - kragen 4y ago
        Nor Rust!
    - pjmlp 4y ago
      Yeah, but that was 40 years ago, back when GCC still stood for GNU C Compiler.
      - kragen 4y ago
        I had pegged it as between 20 and 30 years ago, but someone pointed out that the author said they tried using asan. 40 years ago most universities didn't have Unix boxes accessible to random undergraduates at all. GCC started having parts written in C++ 12 years ago: https://lwn.net/Articles/542457/ https://lwn.net/Articles/542457/
- infogulch 4y ago
  Because it was C I couldn't be sure it was the compiler's fault until I really exhausted every other option. Maybe spent 100h between a few people getting to the end of it. If I had written in safe Rust (I would have, I wasn't doing anything weird) and it segfaulted I'd know immediately that the compiler was the problem because you can't make safe rust segfault.
  - kragen 4y ago
    Yes, that's true.
    - andrewchambers 4y ago
      Or he could do the normal thing and run valgrind to instantly see exactly where the problem is. I don't even disagree with the premise, but these are straw man arguments.
      - kragen 4y ago
        Valgrind didn't exist then. (Next you're going to say ASan and UBSan. Those didn't exist either.) They (he?) could have run GDB and disassembled the code around the crashing instruction and verified that the machine code there didn't make any fucking sense. But that implies they knew assembly language well enough to recognize when their compiler was spewing nonsense, which is a couple of steps above "can read working assembly emitted by the compiler" or even "can write applications in assembly language". Even with Valgrind it can be tough to distinguish whether your output code is wrong because of a bug in the compiler or because your code was just wrong. There was a change to GCC a few years back that introduced security holes into the FreeBSD and NetBSD kernel because it just threw away code that would only be invoked in "undefined behavior" scenarios. Signed integer overflow I think.
        andrewchambers 4y ago
        You are unfairly comparing ancient C with modern rust - Try comparing modern C with modern rust to avoid making a straw man argument. Like I said, I don't even disagree, I still think you are just doing everyone a disservice with this line of reasoning. He said if he had used rust - I am saying if he had used C when rust was available 1. The bug would have been fixed. 2. He could have used valgrind. Modern C also has something called ubsan, and another thing called frama-C. These tools may be inferior to what rust has, but ignoring they exist or comparing 10+ year old C with modern rust is a bad faith argument.
- deleted 4y ago
  [deleted]
- infogulch 4y ago
  Yes perl may have been a better choice for the projects sake, but alas the course was apparently a trial-by-~fire~segfault of C + string processing. Loved PCRE though... hmm I wonder if you could do it with just a regex...
  - kragen 4y ago
    I will be very surprised if you can write a working spreadsheet in a PCRE regex. Perl itself permits you to embed arbitrary Perl code in a "regex", though.
- pjmlp 4y ago
  GCC is being written in C++ for about a decade now.
andrewchambers 4y ago
This is not a good anecdote - You hit a 10 year old bug because your sysadmin was too lazy to update gcc and then formed a bad impression of the software? Guess what, if you install a 10 year old version rust none of your code would not compile at all. Your logic is so flawed its hard to believe you are being serious. If anything it's impressive that a 10 year old C compiler worked most of the time when most other languages are not stable on these timescales.
- duckerude 4y ago
  The oldest rustc version I target (for a tiny project, admittedly) is over 6 years old, and it's fine. When code works it also works on the latest release. When code doesn't work I get a reasonable compile-time error message, not a mysterious segfault at runtime. It's not easy, even in a few hundred lines I had to remove many conveniences to go that far back, but it's very legible. The compiler has my back, I'm never confused about whose fault it is. Rust is young, but I don't expect this to be any different in 2030.
- avgcorrection 4y ago
  > Guess what, if you install a 10 year old version rust none of your code would not compile at all. Rust was not stable in 2012 yet. I do agree with your overall point though.

kragen 4y ago

That's not related to C, except in the sense that GCC is written in C. GCC was just emitting incorrect code because it had a bug in its code generator. If there's a bug in the LLVM code generator (which is written in C++), rustc might end up doing the same thing. If you write the compiler in Rust it could still happen. Rust code (that compiles) has less bugs than the corresponding C but not zero bugs. It doesn't sound like you went overboard, it sounds like a good project. Maybe you should have written it in Perl 5.001 though.

charcircuit 4y ago
GCC is written in C++
- kragen 4y ago
  There are small parts of GCC that are written in C++, but at the time when universities had "one multi-user unix server for all students" it was 100% C.
  - turminal 4y ago
    and there was no LLVM :)
    - kragen 4y ago
      Nor Rust!
  - pjmlp 4y ago
    Yeah, but that was 40 years ago, back when GCC still stood for GNU C Compiler.
    - kragen 4y ago
      I had pegged it as between 20 and 30 years ago, but someone pointed out that the author said they tried using asan. 40 years ago most universities didn't have Unix boxes accessible to random undergraduates at all. GCC started having parts written in C++ 12 years ago: https://lwn.net/Articles/542457/ https://lwn.net/Articles/542457/
infogulch 4y ago
Because it was C I couldn't be sure it was the compiler's fault until I really exhausted every other option. Maybe spent 100h between a few people getting to the end of it. If I had written in safe Rust (I would have, I wasn't doing anything weird) and it segfaulted I'd know immediately that the compiler was the problem because you can't make safe rust segfault.
- kragen 4y ago
  Yes, that's true.
  - andrewchambers 4y ago
    Or he could do the normal thing and run valgrind to instantly see exactly where the problem is. I don't even disagree with the premise, but these are straw man arguments.
    - kragen 4y ago
      Valgrind didn't exist then. (Next you're going to say ASan and UBSan. Those didn't exist either.) They (he?) could have run GDB and disassembled the code around the crashing instruction and verified that the machine code there didn't make any fucking sense. But that implies they knew assembly language well enough to recognize when their compiler was spewing nonsense, which is a couple of steps above "can read working assembly emitted by the compiler" or even "can write applications in assembly language". Even with Valgrind it can be tough to distinguish whether your output code is wrong because of a bug in the compiler or because your code was just wrong. There was a change to GCC a few years back that introduced security holes into the FreeBSD and NetBSD kernel because it just threw away code that would only be invoked in "undefined behavior" scenarios. Signed integer overflow I think.
      - andrewchambers 4y ago
        You are unfairly comparing ancient C with modern rust - Try comparing modern C with modern rust to avoid making a straw man argument. Like I said, I don't even disagree, I still think you are just doing everyone a disservice with this line of reasoning. He said if he had used rust - I am saying if he had used C when rust was available 1. The bug would have been fixed. 2. He could have used valgrind. Modern C also has something called ubsan, and another thing called frama-C. These tools may be inferior to what rust has, but ignoring they exist or comparing 10+ year old C with modern rust is a bad faith argument.
deleted 4y ago
[deleted]
infogulch 4y ago
Yes perl may have been a better choice for the projects sake, but alas the course was apparently a trial-by-~fire~segfault of C + string processing. Loved PCRE though... hmm I wonder if you could do it with just a regex...
- kragen 4y ago
  I will be very surprised if you can write a working spreadsheet in a PCRE regex. Perl itself permits you to embed arbitrary Perl code in a "regex", though.
pjmlp 4y ago
GCC is being written in C++ for about a decade now.

andrewchambers 4y ago

This is not a good anecdote - You hit a 10 year old bug because your sysadmin was too lazy to update gcc and then formed a bad impression of the software? Guess what, if you install a 10 year old version rust none of your code would not compile at all. Your logic is so flawed its hard to believe you are being serious. If anything it's impressive that a 10 year old C compiler worked most of the time when most other languages are not stable on these timescales.

duckerude 4y ago
The oldest rustc version I target (for a tiny project, admittedly) is over 6 years old, and it's fine. When code works it also works on the latest release. When code doesn't work I get a reasonable compile-time error message, not a mysterious segfault at runtime. It's not easy, even in a few hundred lines I had to remove many conveniences to go that far back, but it's very legible. The compiler has my back, I'm never confused about whose fault it is. Rust is young, but I don't expect this to be any different in 2030.
avgcorrection 4y ago
> Guess what, if you install a 10 year old version rust none of your code would not compile at all. Rust was not stable in 2012 yet. I do agree with your overall point though.