cross-compile to armv7-unknown-linux-gnueabihf fails

[stefson]

I'm kind of new to cross-compiling with rust, but I managed to set up a foreign rust-std, and also a gcc cross-compiler for linking. It's all in cargo's config:

$ cat >>~/.cargo/config

[target.armv7-unknown-linux-gnueabihf]
linker = "armv7a-unknown-linux-gnueabihf"

how to reproduce:

git clone https://github.com/nagisa/rust_libloading.git
cd rust_libloading
cargo build --target=armv7-unknown-linux-gnueabihf

    Updating crates.io index
   Compiling cc v1.0.31
   Compiling libloading v0.5.0 (/tmp/rust_libloading)                                                                                                                                   
error: failed to run custom build command for `libloading v0.5.0 (/tmp/rust_libloading)`                                                                                                
process didn't exit successfully: `/tmp/rust_libloading/target/debug/build/libloading-a41fce1a7453006f/build-script-build` (exit code: 101)
--- stdout
cargo:rustc-link-lib=dl
TARGET = Some("armv7-unknown-linux-gnueabihf")
OPT_LEVEL = Some("0")
HOST = Some("x86_64-unknown-linux-gnu")
CC_armv7-unknown-linux-gnueabihf = None
CC_armv7_unknown_linux_gnueabihf = None
TARGET_CC = None
CC = None
CROSS_COMPILE = None
CFLAGS_armv7-unknown-linux-gnueabihf = None
CFLAGS_armv7_unknown_linux_gnueabihf = None
TARGET_CFLAGS = None
CFLAGS = None
CRATE_CC_NO_DEFAULTS = None
DEBUG = Some("true")
CARGO_CFG_TARGET_FEATURE = None
running: "arm-linux-gnueabihf-gcc" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-fno-omit-frame-pointer" "-march=armv7-a" "-Wall" "-Wextra" "-o" "/tmp/rust_libloading/target/armv7-unknown-linux-gnueabihf/debug/build/libloading-b5a400997b94cd58/out/src/os/unix/global_static.o" "-c" "src/os/unix/global_static.c"

--- stderr
thread 'main' panicked at '

Internal error occurred: Failed to find tool. Is `arm-linux-gnueabihf-gcc` installed?

', /home/user/.cargo/registry/src/github.tiyicn.workers.dev-1ecc6299db9ec823/cc-1.0.31/src/lib.rs:2367:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[stefson]

Now, I don't really understand why this happens? .cargo/config is supposed to provide the gcc-linker, why does it end up with this debianism of arm-linux-gnueabihf?

[stefson]

verbose output with RUST_BACKTRACE=1 verbose.zip

[nagisa]

This is looking for a C compiler not a linker. You will need to set <target>_CC=theccompiler before building. The default of <target>-gcc has been guessed by the gcc crate.

…

On Wed, Mar 20, 2019, 13:45 stefson ***@***.***> wrote: verbose output with RUST_BACKTRACE=1 verbose.zip <https://github.com/nagisa/rust_libloading/files/2987948/verbose.zip> — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#51 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AApc0muyyqLylhtMhirjn9kpAFKFCqG_ks5vYh9AgaJpZM4b_GEN> .

[nagisa]

The exact environ variable you need to set is CC_armv7_unknown_linux_ gnueabihf.

…

On Wed, Mar 20, 2019, 13:52 Simonas Kazlauskas ***@***.***> wrote: This is looking for a C compiler not a linker. You will need to set <target>_CC=theccompiler before building. The default of <target>-gcc has been guessed by the gcc crate. On Wed, Mar 20, 2019, 13:45 stefson ***@***.***> wrote: > verbose output with RUST_BACKTRACE=1 verbose.zip > <https://github.com/nagisa/rust_libloading/files/2987948/verbose.zip> > > — > You are receiving this because you are subscribed to this thread. > Reply to this email directly, view it on GitHub > <#51 (comment)>, > or mute the thread > <https://github.com/notifications/unsubscribe-auth/AApc0muyyqLylhtMhirjn9kpAFKFCqG_ks5vYh9AgaJpZM4b_GEN> > . >

[stefson]

hmm, okay, rust_libloading doesn't use rustc at all then?

[nagisa]

It uses both a C and the Rust compiler. The C compiler is necessary to build a tiny snippet of C code that would require an unstable feature in Rust. When the feature becomes stable this crate will not contain any C code at all.

…

On Wed, Mar 20, 2019, 14:02 stefson ***@***.***> wrote: hmm, okay, rust_libloading doesn't use rustc at all then? — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#51 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AApc0pMk4BIiejyNy2ikPvdtQ4zPNSniks5vYiNogaJpZM4b_GEN> .

[stefson]

Would you mind to tell me more about how this feature is called? And in which rust version it's going to be stable, if you happen to know?

[nagisa]

The feature is linkage attribute and it is currently not on a path for stabilisation as it needs design work first.

[nagisa]

Closing as there has been no activity and we’re getting rid of the C component in the next release.

[stefson]

Totally forgot about this one. The reason for this messing up is the crate which determinates the correct gcc symlink, since it only accounts for debian name schemes. A simple symlink from the non debian cross compiler to /usr/bin/arm-linux-gnueabihf-gcc solves the compile issue.

Having done that, libloading v0.5.2 has no issues with cross compiling anymore.

However, there are many warnings:

   Compiling libloading v0.5.2 (/tmp/rust_libloading)
warning: use of deprecated item 'try': use the `?` operator instead
   --> src/os/unix/mod.rs:121:33
    |
121 |             Some(ref f) => Some(try!(cstr_cow_from_bytes(f.as_ref().as_bytes()))),
    |                                 ^^^
    |
    = note: `#[warn(deprecated)]` on by default

warning: use of deprecated item 'try': use the `?` operator instead
   --> src/os/unix/mod.rs:152:22
    |
152 |         let symbol = try!(cstr_cow_from_bytes(symbol));
    |                      ^^^

warning: use of deprecated item 'try': use the `?` operator instead
  --> src/util.rs:45:35
   |
45 |         Some(&0) => Cow::Borrowed(try!(CStr::from_bytes_with_nul(slice))),
   |                                   ^^^

warning: use of deprecated item 'try': use the `?` operator instead
  --> src/util.rs:47:31
   |
47 |         Some(_) => Cow::Owned(try!(CString::new(slice))),
   |                               ^^^

warning: use of deprecated item 'std::mem::uninitialized': use `mem::MaybeUninit` instead
   --> src/os/unix/mod.rs:339:36
    |
339 |             let mut info: DlInfo = mem::uninitialized();
    |                                    ^^^^^^^^^^^^^^^^^^

warning: module `rNEXT` should have a snake case name
 --> src/changelog.rs:9:9
  |
9 | pub mod rNEXT {}
  |         ^^^^^ help: convert the identifier to snake case: `r_next`
  |
  = note: `#[warn(non_snake_case)]` on by default

    Finished dev [unoptimized + debuginfo] target(s) in 0.48s