Cross-platform conflict while linking

[aristarh2704]

Now I try use nightly rustc on cygwin. While compiling libbacktrase-sys, mingw-gcc uses cygwin headers, for example, it take errno value as "__errno()", and after compiling, symbol dumping shows that library has undefined reference to "___errno" (with 3 underscores). While libmsvcrt adds this function named __errno (with 2 underscores). This makes it impossible to compile on the cygwin platform. I think the mingw compiler shipped with rustc must have its own headers.

$ rustc -vV
rustc 1.42.0-nightly (8a79d08fa 2020-01-27)
binary: rustc
commit-hash: 8a79d08fa57e1c257d647c9848e35defcb379c07
commit-date: 2020-01-27
host: i686-pc-windows-gnu
release: 1.42.0-nightly
LLVM version: 9.0

I can use the hack with editing errno.h, but it's not good solution.

[retep998]

Rust does not support Cygwin.

[aristarh2704]

Why does mingw come with the compiler? Indeed, in theory, the system should have its own mingw compiler, if in some situations headers are used

[retep998]

The pc-windows-gnu targets come with a minimal subset of MinGW sufficient to link pure Rust binaries. That currently causes some issues such as #47048 when you also have a full external MinGW toolchain, but #67429 is supposed to fix that so it'll favor your external MinGW toolchain over the bundled MinGW. That said, Rust still does not support Cygwin.

[aristarh2704]

Ok, it's possible define i686-pc-cygwin-gnu?

[mati865]

pc-windows-gnu nightly builds now use system MinGW if available with bundled one as a fallback.

@aristarh2704 do you want to crate binaries for Cygwin or native Windows?

[workingjubilee]

Any hypothetical new target would follow the target tier policy for how to add it, and you are welcome to do so if you also want to do the work of maintaining it. Judging by how often the existing pc-windows-gnu target gets flakey, it would be a LOT of work if you ever wanted it above tier 3. Not for the fainthearted. But if sufficient maintenance comes for it, I suppose we might.

Otherwise, I do not think the windows-gnu target includes cygwin, so closing this.