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by jarjoura 154 days ago
Wouldn't C++ and Rust eventually call down into those same libc functions?

I guess for your example, qsort() it is optional, and you can chose another implementation of that. Though I tend to find that both standard libraries tend to just delegate those lowest level calls to the posix API.
2 comments
steveklabnik 154 days ago
Rust doesn't call into libc for sort, it has its own implementation in the standard library.
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oguz-ismail2 153 days ago
Obviously. How about more complex things like multi-threading APIs though? Can the Rust compiler determine that the subject program doesn't need TLS and produce a binary that doesn't set it up at all, for example?
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dwattttt 153 days ago
Optimising out TLS isn't going to be a good example of compiler capability. Whether another thread exists is a global property of a process, and beyond that the system that process operates in.

The compiler isn't going to know for instance that an LD_PRELOAD variable won't be set that would create a thread.

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oguz-ismail2 153 days ago
> Whether another thread exists is a global property of a process, and beyond that the system that process operates in.

TLS is a language feature. Whether another thread exists doesn't mean it has to use the same facilities as the main program.

> The compiler isn't going to know for instance that an LD_PRELOAD variable won't be set that would create a thread.

Say the program is not dynamically linked. Still no?

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dwattttt 153 days ago
> Say the program is not dynamically linked. Still no?

Whether the program has dynamic dependencies does not dictate whether a thread can be created, that's a property of the OS. Windows has CreateRemoteThread, and I'd be shocked if similar capabilities didn't exist elsewhere.

If I mark something as thread-local, I want it to be thread-local.

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steveklabnik 153 days ago
I mean, it’s not that obvious, your parent asked about it directly, and you could easily imagine calling it libc for this.

I beehive the answer to your question is “yes” because no-std binaries can be mere bytes in size, but I suspect that more complex programs will almost always have some dependency somewhere (possibly even the standard library, but I don’t know offhand) that uses TLS somewhere in it.

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adgjlsfhk1 153 days ago
Many of the libc functions are bad apis with traditionally bad implementations.
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