Support setting "-C linker=" for rustc

[hukka]

Some cross compilation tools have prefixes in their name and path, for example the armel linker on Debian is /usr/bin/arm-linux-gnueabi-gcc. Cross compile targets would need a way to specify -C linker for rustc in the manifest.

[alexcrichton]

This is currently possible today via target.$triple.linker, and more flags are covered by #544.

[hukka]

Mea culpa. Missed that whole page and just read the guide and the manifest docs.

[mpe]

For anyone else who doesn't read the documentation properly, the target.$triple.linker settings goes in .cargo/config not in Cargo.toml. If you put it in Cargo.toml it will be silently ignored.

eg:

[target.arm-unknown-linux-gnueabi]
linker = "/usr/bin/arm-linux-gnueabi-gcc"

[tigerleapgorge]

If you put it in Cargo.toml it will be silently ignored.

Isn't that rather error prone?

[rightfold]

How do I find my target triple?

[alexcrichton]

@rightfold if you run rustc -vV it'll tell you the default target that you compile for (under host), otherwise you're passing --target in which case that's the target triple.

[rightfold]

Thanks! 😃 Sent from my iPhone.

…

Op 12 feb. 2017 om 06:26 heeft Alex Crichton ***@***.***> het volgende geschreven: @rightfold if you run rustc -vV it'll tell you the default target that you compile for (under host), otherwise you're passing --target in which case that's the target triple. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or mute the thread.

[jeroen]

Is there any way to set the linker via an environment variable or cargo parameter rather than a config file?

[alexcrichton]

@jeroen you should be able to set configuration via env vars

[jeroen]

@alexcrichton what environment variable would I use to set the linker for target.x86_64-pc-windows-gnu and target.i686-pc-windows-gnu?

[jeroen]

Or just in general can I set the linker for the current cargo build (any target) with an environment variable? I tried:

• LD
• LINKER
• CARGO_BUILD_LINKER
• CARGO_TARGET_i686-pc-windows-gnu_LINKER

But none had the same effect as a config file containing:

[target.i686-pc-windows-gnu]
linker = "c:/Rtools/mingw_32/bin/gcc"

[alexcrichton]

@jeroen you'd use CARGO_TARGET_I686_PC_WINDOWS_GNU_LINKER

[jeroen]

Thanks @alexcrichton! Now I am stuck on one final issue:

We use a version of mingw-builds that was compiled with --static-gcc. Therefore our toolchain does not contain a copy of libgcc_eh.a, instead those objects are available from libgcc.a.

Currently when I try to build imageoptim-sys the linker fails because it can't find libgcc_eh.a. I think that is because this flag is hardcoded in rust. Is there some way I can tell rust that my linker wants to be linked with -lgcc instead of -lgcc_eh?

The cmake folks have a similar topic about not linking to libgcc_eh directly.

[alexcrichton]

@jeroen ah unforutnately you can't change that right now, so the only recourse would be to write a wrapper script that translates -lgcc_eh to -lgcc, it's not great :(

[lobianco]

For anyone who stumbles into this thread looking for an answer that doesn't involve .cargo/config, you can set the linker as a parameter of your cargo command like this:

RUSTFLAGS="-C linker=/path/to/linker" cargo run ...

[sanmai-NL]

@jeroen ah unforutnately you can't change that right now, so the only recourse would be to write a wrapper script that translates -lgcc_eh to -lgcc, it's not great :(

See rust-lang/rust#29527