Cross-compile rust libs for ARMv5 target

[joerg-krause]

I want to cross-compile the rust libs, eg std, for an ARMv5 target. For now, I am able to cross-compile libcore with an armv5te-none-eabi.json target and cross-compile a no-std program without the libc crate by linking with a target libc from musl.

However, I am not sure how to cross-compile the std library for the ARMv5 target as the included target arm-unknown-linux-gnueabi builds for ARMv6.

[MagaTailor]

What if you modified the target to use v5?
Together with arm-unknown-linux-gnueabi.mk.

[joerg-krause]

My first attempt was to create a new target armv5te-unknown-linux-gnueabi.mk, but this fails because my host (Arch Linux) rust compiler backend does not include such a target.

My second attempt was to replace the existing arm-unknown-linux-gnueabi.mk target with:

# arm-unknown-linux-gnueabi configuration
CROSS_PREFIX_arm-unknown-linux-gnueabi=arm-linux-gnueabi-
CC_arm-unknown-linux-gnueabi=gcc
CXX_arm-unknown-linux-gnueabi=g++
CPP_arm-unknown-linux-gnueabi=gcc -E
AR_arm-unknown-linux-gnueabi=ar
CFG_LIB_NAME_arm-unknown-linux-gnueabi=lib$(1).so
CFG_STATIC_LIB_NAME_arm-unknown-linux-gnueabi=lib$(1).a
CFG_LIB_GLOB_arm-unknown-linux-gnueabi=lib$(1)-*.so
CFG_LIB_DSYM_GLOB_arm-unknown-linux-gnueabi=lib$(1)-*.dylib.dSYM
CFG_JEMALLOC_CFLAGS_arm-unknown-linux-gnueabi := -D__arm__ -msoft-float $(CFLAGS)
CFG_GCCISH_CFLAGS_arm-unknown-linux-gnueabi := -Wall -g -fPIC -D__arm__ -msoft-float $(CFLAGS)
CFG_GCCISH_CXXFLAGS_arm-unknown-linux-gnueabi := -fno-rtti $(CXXFLAGS)
CFG_GCCISH_LINK_FLAGS_arm-unknown-linux-gnueabi := -shared -fPIC -g -msoft-float
CFG_GCCISH_DEF_FLAG_arm-unknown-linux-gnueabi := -Wl,--export-dynamic,--dynamic-list=
CFG_LLC_FLAGS_arm-unknown-linux-gnueabi :=
CFG_INSTALL_NAME_arm-unknown-linux-gnueabi =
CFG_EXE_SUFFIX_arm-unknown-linux-gnueabi :=
CFG_WINDOWSY_arm-unknown-linux-gnueabi :=
CFG_UNIXY_arm-unknown-linux-gnueabi := 1
CFG_LDPATH_arm-unknown-linux-gnueabi :=
CFG_RUN_arm-unknown-linux-gnueabi=$(2)
CFG_RUN_TARG_arm-unknown-linux-gnueabi=$(call CFG_RUN_arm-unknown-linux-gnueabi,,$(2))
RUSTC_FLAGS_arm-unknown-linux-gnueabi :=
RUSTC_CROSS_FLAGS_arm-unknown-linux-gnueabi := -C target-cpu=arm926ej-s -C target-feature="+v5te" -C soft-float
CFG_GNU_TRIPLE_arm-unknown-linux-gnueabi := arm-unknown-linux-gnueabi

... and the librustc target backend arm_unknown_linux_gnueabi.rs with:

use target::Target;

pub fn target() -> Target {
    Target {
        llvm_target: "arm-unknown-linux-gnueabi".to_string(),
        target_endian: "little".to_string(),
        target_pointer_width: "32".to_string(),
        arch: "arm".to_string(),
        target_os: "linux".to_string(),
        target_env: "gnueabi".to_string(),
        target_vendor: "unknown".to_string(),
        options: super::linux_base::opts()
    }
}

Cross-compiling rust:

$ ./configure --target=arm-unknown-linux-gnueabi --prefix=$HOME/rust-cross --disable-jemalloc
$ make
$ make install
$ LD_LIBRARY_PATH=$HOME/rust-cross/lib $HOME/rust-cross/bin/rustc --version
rustc 1.7.0-dev (4c111e990 2016-01-05)

I need to configure Rust with --disable-jemalloc otherwise building hello world will fail with:

note: /home/joerg/rust-cross/lib/rustlib/arm-unknown-linux-gnueabi/lib/liballoc_jemalloc-ca1c970e.rlib(jemalloc.pic.o): In function `secure_getenv':
/home/joerg/git/rust/src/jemalloc/src/jemalloc.c:734: undefined reference to `issetugid'

As building rust with --disable-jemalloc is currently broken (#30592) I had to patch current HEAD revision (dbacacd) with simartin@4c68110 and simartin@4c111e9.

Cross-compile hello:

$ cat hello.rs 
fn main() {
    println!("Hello, world!");
}
$ LD_LIBRARY_PATH=$HOME/rust-cross/lib $HOME/rust-cross/bin/rustc --target=arm-unknown-linux-gnueabi -C linker=/usr/bin/arm-linux-gcc hello.rs
$ file hello 
hello: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 2.6.32, not stripped
$ size hello 
   text    data     bss     dec     hex filename
 115129    2452      68  117649   1cb91 hello

Running on target:

$ ./hello 
Hello, world!

Finally, it works!!!

I am very new to Rust and I will be happy about any comments or suggestions. Furthermore, I would be glad if we can have a ARMv5(te) target with soft float supported by Rust.

My next attempt will be to cross-compile using the musl library (instead of glibc).

[MagaTailor]

What host are you building the cross-compiler on? And btw, it's no longer necessary to set LD_LIBRARY_PATH I believe.

[joerg-krause]

Host is Arch Linux.

[MagaTailor]

I meant host architecture.

[joerg-krause]

Host architecture is x86_64.

[MagaTailor]

Alright, if you continue experimenting with custom targets, remember to add them to mod.rs before trying to bootstrap the compiler.

[joerg-krause]

I followed the explanations from https://doc.rust-lang.org/nightly/book/advanced-linking.html#linux to build a musl-enabled Rust. However, using my arm-unknown-linux-musl target (https://gist.github.com/joerg-krause/7a7351b6e4ae7267a0ae) fails with some mismatched types errors, like:

[..]
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/arm-unknown-linux-musl/lib/libstd
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd
warning: dropping unsupported crate type `dylib` for target `arm-unknown-linux-musl`
../src/libstd/dynamic_lib.rs:111:37: 111:56 error: mismatched types:
 expected `*const i8`,
    found `*const u8`
(expected i8,
    found u8) [E0308]
[..]

Any idea what's wrong here?

[MagaTailor]

Ah, yes - I'm an expert on that ;)

#29867

[joerg-krause]

Ouch! Does it mean I have to fix the std library?

[joerg-krause]

Okay, I guess https://github.com/rust-lang-nursery/libc/blob/master/src/unix/notbsd/linux/musl.rs#L9 is not true for ARM devices. The ARM architecture defines char as unsigned, wheras x86(_64) defines it as signed.

[MagaTailor]

You'll probably have to add some casts if you want to compile it from this machine - is it just this one instance or are there more?

[joerg-krause]

A lot more.

I'll try to patch libc by editing https://github.com/rust-lang-nursery/libc/blob/master/src/unix/notbsd/linux/musl.rs#L9:

#[cfg(target_arch = "arm")]
pub type c_char = u8;
#[cfg(not(target_arch = "arm"))]
pub type c_char = i8;

Unfortunatly, building rust takes really long ...