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  • > Imagine a definition of g() that calls exit() if b is zero.

    Imagine a definition of g() that uses longjmp to jump out of f to a jmp_buf context set up by a caller of f bypassing the division by b in the abstract semantics.

    by kazinator
  • i've seen static analyzers catch many ub patterns, but guaranteeing zero ub needs whole‑program analysis that blows up compile time and still produces false positives that drown developers
    by elais-dev
  • We need to learn to use assembly and call it from C. C was never meant to be the end of programming. Reducing undefined behavior is the least the standards body can do. Fil-C is also an extremely useful tool.

    The real problem I see is the inability of independent compiler writers upgrading to the latest standard. I think this is also an issue that the standards body should pay attention. Help implementers.

    by fithisux
  • I believe this is barking up the wrong tree since IMHO C is just "high level assembly" for systems programming. As soon as you add runtime behavior to combat Undefined Behavior (UB) you're blowing up execution times. And static analysis can only go so far without blowing up compile times.

    C is "the right tool for the right job" which is operating systems and its code which is called thousands of times per second. You cannot afford even one iota of runtime checks in that code. The developer must know what he's doing or he should get out of the kitchen.

    We should discourage the usage of C in application programming and prod application developers towards memory safe languages like Rust or Go.

    And I'm not even sure if Rust solves this case as far as UB is concerned.

    by hn_submit
  • 1790620504 | Reducing undefined behavior in the C language | https://lwn.net/SubscriberLink/1095811/b9325731ea9b61e0/ | https://news.ycombinator.com/item?id=49882419 | 15 comments

    1790673092 | Reducing undefined behavior in the C language | https://lwn.net/SubscriberLink/1095811/efcdbcf080cfa4c6/ | https://news.ycombinator.com/item?id=49890290 | 0 comments

    by 1vuio0pswjnm7
  • My main issue with UB in C is that it's silent.

    I'm OK with compiler doing wild thing, OK, whatever. Well, I'm not OK but I can accept it in this crazy world.

    But I want to have loud warnings! Like WARNING: this conditional operator has been collapsed to one branch because earlier division by zero is UB. And now I can notice it and rewrite it or just remove that condition.

    I understand that this code can be result of macro expansion. That's OK. Macros should either include some pragmas to temporary disable specific diagnostics or user should surround macro usage with these pragmas, if they can't edit the macro. It's already happening with other warnings.

    Or maybe compiler could be smart enough to distinguish macro expansion from honest user mistake, I don't know.

    I remember when C++ compiler just removed function epilogue where I wrote simple infinite loop. That was so crazy. So instead of entering the infinite loop, my program just continued to execute the function that happened to be linked below. Imagine debugging that. Zero diagnostics.

    by vbezhenar
  • It’s cool that this mentions Fil-C but it also undersells it. TFA also undersells CHERI. Fil-C doesn’t just “find a lot of temporal-safety” bugs. It closes off memory safety bugs (special and temporal) for exploit writers and ascribes a tight semantics to the whole language. CHERI makes some different trade offs but also gives a tight enough semantics that memory safety exploits aren’t going to work. Both CHERI and Fil-C are more comprehensive than Rust, since they attack the problem at the ABI level (and so you don’t get the problem that the protection only applies to the parts that were rewritten in the safe subset of a new language). Rust could be claimed to be better in that its compile time, but that doesn’t make a significant difference if you’re worried about the definedness of semantics or exploitability.
    by pizlonator
  • "Some Honeywell machines, for example, had nine-bit bytes."

    OS 2200 has 36-bit words. It is still a supported platform.

    https://en.wikipedia.org/wiki/UNIVAC_1100/2200_series

    This platform was the first SMP UNIX implementation:

    "Any configuration supplied by Sperry, including multiprocessor ones, can run the UNIX system."

    https://www.nokia.com/bell-labs/about/dennis-m-ritchie/other...

    by chasil

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