Figure out how to get static linkage for MSVCRT

[brson]

In order to get the MSI installers working we need to build with the MSVC toolchain and link statically to the CRT.

@alexcrichton without an upstream solution how can we solve this the hard way? I'm thinking something like:

• Modify gcc-rs to interpret some environment variable to mean pass /MT, in a fork if necessary
• Build our own i686-pc-windows-msvc toolchain while setting that environment variable
• Use that toolchain to build rustup, while setting the environment variable

cc #635 (comment)
cc rust-lang/rfcs#1684
cc @Boddlnagg @retep998

[retep998]

The libc crate forces msvcrt.lib to be linked. Either it would have to be modified both for crates.io and the one used in std, or you'd have to set the linker to a wrapper program that strips any mentions of msvcrt.lib before forwarding it on to the actual linker.

Aside from libc, there's nothing else in rust itself that would have to be fixed to solve it the hard way.

In addition to gcc-rs, there is also cmake-rs and anything else that has a build script which compiles C/C++ code in some way.

[brson]

Maybe the linker wrapper is the easiest solution to all these. We can strip msvcrt.lib and convert /MD to /MT.

So we don't need to build a custom toolchain at all, right? Just fix the linker invocation? Is there just one invocation of link.exe globally here, for the final exe/dll? This seems almost easy...

[retep998]

/MD and /MT are flags passed to cl.exe for C/C++ code, not link.exe.

[brson]

So that sounds like we do need a custom toolchain.

• Create a new static-link.exe project that strips the msvcrt.lib
• Modify gcc-rs to interpret some environment variable to mean pass /MT, in a fork if necessary
• Build our own i686-pc-windows-msvc toolchain while setting that environment variable
• Use that toolchain to build rustup, while setting the environment variable and the fake linker

[retep998]

@brson If you do use a linker wrapper, then there is no need to rebuild the Rust toolchain. There is no C/C++ code in libstd and friends that could be affected. There is in rustc itself but that has no effect on code built by rustc.

[Boddlnagg]

To pass /MT in gcc-rs I just used a local fork with a cargo override. A [replace] in Cargo.toml should be sufficient, right (in addition to the linker wrapper)?

[alexcrichton]

@brson I think custom linker shenanigans would work here, but having never done it I'm not 100% sure it'd actually work.

[brson]

To pass /MT in gcc-rs I just used a local fork with a cargo override. A [replace] in Cargo.toml should be sufficient, right (in addition to the linker wrapper)?

I think so.

[retep998]

If this does turn out to work, then I can totally use this as an example to push along my RFC.

[retep998]

This can now be implemented fairly easily considering Rust now has a built in way to link to the static CRT. rust-lang/rust#37406

[tesuji]

@kinnison I think this issue is resolved.