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rust-lang / wg-cargo-std-aware

Repo for working on "std aware cargo"
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Adjust libstd to make non-Rust dependencies optional #54

Open nagisa opened 4 years ago

nagisa commented 4 years ago

Cross-compiling C dependencies is a major pain. The only such dependency libstd has currently to the best of my knowledge is backtrace-sys. I would much rather have an easy time building libstd without an ability to produce backtraces than having to fiddle getting full toolchain set-up for a thing as obscure as, say, netbsd.

RalfJung commented 4 years ago

FWIW, here's the libstd feature config that Miri uses to avoid any C dependencies. Since https://github.com/rust-lang/backtrace-rs/pull/297 landed, that avoids any C dependency, and we have CI on the Miri side to ensure this remains the case.

Another problem is that libstd by default is built as rlib and dylib, and building a dylib also usually requires a target toolchain. However, std-aware cargo might already work around this, I am not sure. (Miri works around this by only doing a check-build of libstd.)

ehuss commented 4 years ago

However, std-aware cargo might already work around this, I am not sure.

There is a hack in Cargo to force it to skip the dylib. You even commented on it. 😜 Ideally there would be first-class support for that, but that is off-topic.

RalfJung commented 4 years ago

Ah lol, my memory is getting worse it seems. ;) But good to hear that that will not be a problem! That solution is not accessible to Miri, but we have our own solution, so that's okay.

joshtriplett commented 3 years ago

At this point, std now uses gimli rather than libbacktrace.

runiq commented 3 years ago

Triage: Given that the only C dependency has been replaced with a Rust dependency, can this be closed or is the underlying issue still worth solving?

RalfJung commented 3 years ago

I'd say the underlying issue has been solved -- even working backtraces requires no non-Rust dependency.

ehuss commented 3 years ago

linux-musl still requires a C compiler (and I think fortanix-sgx does, too). I'm not sure if there needs to be 100% coverage for all targets, but I'm not sure where to draw the line.

12101111 commented 3 years ago

linux-musl still requires a C compiler (and I think fortanix-sgx does, too). I'm not sure if there needs to be 100% coverage for all targets, but I'm not sure where to draw the line.

I'm working on refactoring libunwind and the c/c++ part will not link into libunwind.rlib ( by kind = "static-nobundle" or kind = "static", modifiers = "-bundle" from linking modifiers rfc), It will copy to self-contained directory by rustbuild. If we handle https://github.com/rust-lang/wg-cargo-std-aware/issues/46 properly , the linker will use libunwind.a either from old self-contained directory or provided by system, and unwind crate don't need c/c++ compiler to compile. https://github.com/rust-lang/rust/pull/85600