Compilation for mips64-unknown-linux-gnu

[operutka]

I'm trying to compile the std crate using a custom target specification for mips64-unknown-linux-gnu. I've got stuck a little and I'd appreciate a little help. My specification is a copy of the built-in specification for mips64-unknown-linux-gnuabi64 with the following differences:

1. The data-layout field has been changed to match the data layout used in clang for the same target.
2. The is-builtin field has been set to false.
3. The llvm-target field has been set to mips64-unknown-linux-gnu.
4. The max-atomic-width field has been set to 32 (it was 64 before).
5. The target-pointer-width field has been set to 32 to match the data layout.

This is the whole target specification:

{
  "arch": "mips64",
  "cpu": "mips64r2",
  "data-layout": "E-m:e-p:32:32-i8:8:32-i16:16:32-i64:64-n32:64-S128",
  "dynamic-linking": true,
  "env": "gnu",
  "executables": true,
  "features": "+mips64r2",
  "has-elf-tls": true,
  "has-rpath": true,
  "is-builtin": false,
  "linker-flavor": "gcc",
  "linker-is-gnu": true,
  "llvm-target": "mips64-unknown-linux-gnu",
  "max-atomic-width": 32,
  "os": "linux",
  "position-independent-executables": true,
  "pre-link-args": {
    "gcc": [
      "-Wl,--as-needed",
      "-Wl,-z,noexecstack"
    ]
  },
  "relro-level": "full",
  "target-c-int-width": "32",
  "target-endian": "big",
  "target-family": "unix",
  "target-pointer-width": "32",
  "vendor": "unknown"
}

I end up with the following output:

   Compiling compiler_builtins v0.0.0 (file:///root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/rustc/compiler_builtins_shim)
   Compiling std v0.0.0 (file:///root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd)
     Running `rustc --crate-name build_script_build /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/rustc/compiler_builtins_shim/../../libcompiler_builtins/build.rs --crate-type bin --emit=dep-info,link -C opt-level=3 --cfg 'feature="c"' --cfg 'feature="compiler-builtins"' --cfg 'feature="default"' --cfg 'feature="rustbuild"' -C metadata=90fbb7fd0c7442d5 -C extra-filename=-90fbb7fd0c7442d5 --out-dir /tmp/xargo.606pX8cxT6GH/target/release/build/compiler_builtins-90fbb7fd0c7442d5 -L dependency=/tmp/xargo.606pX8cxT6GH/target/release/deps --extern cc=/tmp/xargo.606pX8cxT6GH/target/release/deps/libcc-786ac8d380309a5a.rlib`
     Running `rustc --crate-name build_script_build /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/build.rs --crate-type bin --emit=dep-info,link -C opt-level=3 -C metadata=0e769dbdf5eed459 -C extra-filename=-0e769dbdf5eed459 --out-dir /tmp/xargo.606pX8cxT6GH/target/release/build/std-0e769dbdf5eed459 -L dependency=/tmp/xargo.606pX8cxT6GH/target/release/deps --extern build_helper=/tmp/xargo.606pX8cxT6GH/target/release/deps/libbuild_helper-ca4cc909bb4adcb1.rlib --extern cc=/tmp/xargo.606pX8cxT6GH/target/release/deps/libcc-786ac8d380309a5a.rlib`
     Running `/tmp/xargo.606pX8cxT6GH/target/release/build/std-0e769dbdf5eed459/build-script-build`
     Running `/tmp/xargo.606pX8cxT6GH/target/release/build/compiler_builtins-90fbb7fd0c7442d5/build-script-build`
warning: ../../libcompiler_builtins/compiler-rt/lib/builtins/divdc3.c:21:1: warning: conflicting types for built-in function '__divdc3'
warning:  __divdc3(double __a, double __b, double __c, double __d)
warning:  ^
warning: ../../libcompiler_builtins/compiler-rt/lib/builtins/divsc3.c:21:1: warning: conflicting types for built-in function '__divsc3'
warning:  __divsc3(float __a, float __b, float __c, float __d)
warning:  ^
warning: ../../libcompiler_builtins/compiler-rt/lib/builtins/muldc3.c:21:1: warning: conflicting types for built-in function '__muldc3'
warning:  __muldc3(double __a, double __b, double __c, double __d)
warning:  ^
warning: ../../libcompiler_builtins/compiler-rt/lib/builtins/mulsc3.c:21:1: warning: conflicting types for built-in function '__mulsc3'
warning:  __mulsc3(float __a, float __b, float __c, float __d)
warning:  ^
LLVM ERROR: Not supported instr: <MCInst 0 <MCOperand Reg:416> <MCOperand Reg:321>>
error: Could not compile `core`.

Caused by:
  process didn't exit successfully: `rustc --crate-name core /root/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/lib.rs --crate-type lib --emit=dep-info,link -C opt-level=3 -C panic=abort -C metadata=59ab99930ed6da97 -C extra-filename=-59ab99930ed6da97 --out-dir /tmp/xargo.606pX8cxT6GH/target/mips64-unknown-linux-gnu/release/deps --target mips64-unknown-linux-gnu -C ar=mips64-buildroot-linux-gnu-ar -C linker=mips64-buildroot-linux-gnu-gcc -L dependency=/tmp/xargo.606pX8cxT6GH/target/mips64-unknown-linux-gnu/release/deps -L dependency=/tmp/xargo.606pX8cxT6GH/target/release/deps --sysroot /root/.xargo -Z force-unstable-if-unmarked` (exit code: 1)
error: `"cargo" "build" "--release" "--manifest-path" "/tmp/xargo.606pX8cxT6GH/Cargo.toml" "--target" "mips64-unknown-linux-gnu" "-v" "-p" "std"` failed with exit code: Some(101)
note: run with `RUST_BACKTRACE=1` for a backtrace

The reason why I'm trying this is that I have an existing Debian system with this target (it's Ubiquiti EdgeRouter) and I'd like to compile a Rust application for this system. It's a big endian MIPS64 system with n32 ABI. Unfortunately, Rust supports only n64.

[operutka]

Steps to reproduce:

1. Switch to Rust nightly, update and get the rust-src component:

rustup toolchain add nightly
rustup update
rustup default nightly
rustup component add rust-src

2. Install xargo:

cargo install xargo

3. Get a mips64-unknown-linux-gnu toolchain and set some env. variables:

wget http://download.angelcam.com/toolchains/mips64-buildroot-linux-gnu.tar.gz
tar xzf mips64-buildroot-linux-gnu.tar.gz
export PATH=$(pwd)/mips64-buildroot-linux-gnu/usr/bin:$PATH
export CC_mips64_unknown_linux_gnu=mips64-buildroot-linux-gnu-gcc

4. Create a dummy Rust project:

cargo new dummy
cd dummy

5. Put the target specification mentioned above into mips64-unknown-linux-gnu.json.
6. Create .cargo/config:

mkdir .cargo
cat << EOF > .cargo/config
[target.mips64-unknown-linux-gnu]
ar = "mips64-buildroot-linux-gnu-ar"
linker = "mips64-buildroot-linux-gnu-gcc"
EOF

7. Build the project:

xargo build --target mips64-unknown-linux-gnu --verbose

Note: This dummy project actually dies when building the core crate but with the same error.

[draganmladjenovic]

I haven't tried to reproduce this issue yet, but only json specification won't work. You need somehow to pass ABI information akin to clang/llc's "-mabi=n32" to the LLVM backend because MIPS target can't infer n32 ABI from the target triple and arch alone.

[operutka]

I've checked the librustc_target crate and I haven't found any option to pass -mabi=XXX to LLVM. Is it even possible? Or maybe a better question - could you point me to the code responsible for telling LLVM which ABI it should use?

[draganmladjenovic]

Probably you should look here

rust/src/rustllvm/PassWrapper.cpp

Line 355 in dbd10f8

extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(

and set Options.MCOptions.ABIName to "n32" (http://llvm.org/doxygen/classllvm_1_1TargetOptions.html#a3cdbd949eef9cd8a1d5267d627cd9fb1).

[operutka]

Thanks. It seems like I'll have to find some time to build the whole Rust.

[draganmladjenovic]

Hi, Sorry I still haven't found time to verify it myself, but I also think that you JSON spec file should contain something no_integrated_as: true and asm_args : "-mabi=n32". N32 seems to be unfinished on LLVM 6.0 so relaying on GNU AS might help. Best regards.

[operutka]

OK, I'll try it with GNU AS at first. Thanks.

[operutka]

I've tried it with the "no_integrated_as" option in the JSON target specification but I'm not sure if it had any effect. It ended up with the same LLVM error. I also did a second experiment where I passed -C no-integrated-as to rustc via cargo config and the compiler ended up with SIGSEGV.

[wzssyqa]

Debian's N32 triples support has been merged just only, and maybe you can have a try with
mips64-unknown-linux-gnuabin32
not
mips64-unknown-linux-gnu

In Debian with use gnuabin32 instead of just -gnu for n32.

[wzssyqa]

and Ubiquiti EdgeRouter is endian switchable, I guess you can have a try mips64el.

[operutka]

Thanks a lot. I really appreciate it. I'll try it next week.

[operutka]

I forgot about this for a while and got back to it today again. These are my updates:

I've tested it with a custom target specification for mips64-unknown-linux-gnuabin32 and the compilation itself works, however, I'm unable to link libstd because xargo seems to be stubborn and uses system linker instead of my cross-linker. I guess I'll have to wait until the xargo features are ready in cargo.

[nw0]

Are you still pursuing this issue?

I managed to get a process working for a different architecture, but with similar linkage issues. This only went as far as libcore and liballoc, however.

1. Compile a dylib or "Rust library" for the relevant libraries; see documentation on linkage
2. Use rustc to emit LLVM IR, linking to the libraries with --extern
3. Run llc to produce object files targeting your abi
4. Clang should successfully link the resulting object files with your dynamic libs.

You may be able to skip one or more of the above steps.

I can provide more detailed help; the above is something I tried in April (c. 1.35 nightly).