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by estebank 925 days ago
> Rust certainly performs runtime bounds-checking as well as some other tasks, so there is runtime code (even if it's just compiled into executables.)

I don't think I've ever seen anyone reference "C with bounds checks enabled" as "having a runtime". Does having stack probes also imply having a runtime? I guess I'd be less surprised if it had been worded as "some mitigations/features have a runtime cost".

> If you want features like async (standard in many language runtimes) you're also going to have to pull in some kind of external runtime dependency.

Yes, you can add a runtime to your application (if you need to use async/await). It has an additional cost over not doing that, but the "promise" is that it is "zero (additional) cost (over what you'd end up with if you wrote the functionality by hand)".
1 comments
mike_hearn 925 days ago
For sure C programs have a runtime. I'm debugging an issue right now that is to do with Windows not shipping VCRUNTIME140_1.DLL on out-of-the-box or old versions of Win10, so in that case it's very clear because you can make C programs that won't start due to a missing runtime library.

The runtime isn't all that large but every OS has one. On UNIX it's spread over libc, libpthread, libgcc, libm and so on.

On Linux stack probes usually have some support code in libgcc and/or glibc, if I recall correctly.

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biorach 925 days ago
That's a rather idiosyncratic definition of "runtime"
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steveklabnik 925 days ago
(not the parent) You're not wrong but you're not right either. There's basically a colloquialism where many developers say "runtime" to mean "large runtime" and "no runtime" to mean "small runtime," but that doesn't mean that crt0, the "c runtime starting from zero", doesn't exist, just that we've ended up in a place where this gets confusing to talk about because nobody uses the same definitions.

So if it's idiosyncratic really depends on what audience you're talking to.

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mike_hearn 925 days ago
It's the correct definition and I don't know of anyone familiar with OS design that would claim C doesn't have a runtime. It very much does. So does C++. Every language does, except assembly.

It may feel like C doesn't have a runtime if you're only familiar with UNIX, because the C runtime is guaranteed to come with the OS there whereas other language runtimes are optional and thus more visible. But every language has a runtime.

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