bfc does not compile on ARM

[MagaTailor]

The issue I've been tracking from the beginning says hullo:

 Compiling bfc v1.3.0 (file:///tmp/bfc-master)
src/llvm.rs:44:38: 44:49 error: mismatched types:
 expected `*const u8`,
    found `*mut i8`
(expected u8,
    found i8) [E0308]
src/llvm.rs:44         let llvm_ir = CStr::from_ptr(llvm_ir_ptr);
                                                    ^~~~~~~~~~~
src/llvm.rs:44:38: 44:49 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to previous error
Could not compile `bfc`.

Also, please update tempfile in Cargo.toml due to the same issue.

[MagaTailor]

Well no, that was an old source file. Nowadays it's going to need more casts:

Compiling bfc v1.4.0 (file:///tmp/bfc-master)
src/llvm.rs:53:42: 53:53 error: mismatched types:
 expected `*const u8`,
    found `*mut i8`
(expected u8,
    found i8) [E0308]
src/llvm.rs:53             let llvm_ir = CStr::from_ptr(llvm_ir_ptr);
                                                        ^~~~~~~~~~~
src/llvm.rs:53:42: 53:53 help: run `rustc --explain E0308` to see a detailed explanation
src/llvm.rs:270:36: 270:66 error: mismatched types:
 expected `*const i8`,
    found `*const u8`
(expected i8,
    found u8) [E0308]
src/llvm.rs:270         LLVMSetTarget(llvm_module, target_triple_cstring.as_ptr());
                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/llvm.rs:270:36: 270:66 help: run `rustc --explain E0308` to see a detailed explanation
src/llvm.rs:773:40: 773:57 error: mismatched types:
 expected `*const u8`,
    found `*mut i8`
(expected u8,
    found i8) [E0308]
src/llvm.rs:773         target_triple = CStr::from_ptr(target_triple_ptr).to_owned();
                                                       ^~~~~~~~~~~~~~~~~
src/llvm.rs:773:40: 773:57 help: run `rustc --explain E0308` to see a detailed explanation
src/llvm.rs:803:41: 803:53 error: mismatched types:
 expected `*const i8`,
    found `*const u8`
(expected i8,
    found u8) [E0308]
src/llvm.rs:803                                         cpu.as_ptr(),
                                                        ^~~~~~~~~~~~
src/llvm.rs:803:41: 803:53 help: run `rustc --explain E0308` to see a detailed explanation
src/llvm.rs:804:41: 804:58 error: mismatched types:
 expected `*const i8`,
    found `*const u8`
(expected i8,
    found u8) [E0308]
src/llvm.rs:804                                         features.as_ptr(),
                                                        ^~~~~~~~~~~~~~~~~
src/llvm.rs:804:41: 804:58 help: run `rustc --explain E0308` to see a detailed explanation
src/llvm.rs:843:56: 843:65 error: mismatched types:
 expected `*const u8`,
    found `*mut i8`
(expected u8,
    found i8) [E0308]
src/llvm.rs:843             println!("obj_error: {:?}", CStr::from_ptr(obj_error));
                                                                       ^~~~~~~~~
<std macros>:2:25: 2:56 note: in this expansion of format_args!
<std macros>:3:1: 3:54 note: in this expansion of print! (defined in <std macros>)
src/llvm.rs:843:13: 843:68 note: in this expansion of println! (defined in <std macros>)
src/llvm.rs:843:56: 843:65 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to 6 previous errors
Could not compile `bfc`.

So, after casting llvm_ir_ptr as *const _ and so on I managed to get it to compile. It works as expected.

[Wilfred]

Yikes. I've upgraded to the latest libc, but sounds like we'll still need those casts. Would you like to send a pull request?

[MagaTailor]

No problem. Give me a few minutes.

[Wilfred]

Closed by #5.

[MagaTailor]

Hi again,

Another one has just popped up ;)

src/llvm.rs:795:51: 795:62 error: mismatched types:
 expected `*const u8`,
    found `*mut i8`
(expected u8,
    found i8) [E0308]
src/llvm.rs:795                 let err_msg_cstr = CStr::from_ptr(err_msg_ptr);

Have you considered a possible switch away from libc in favour of std::os::raw?

[Wilfred]

OK, I've removed the dependency on libc -- we're not actually using it.

[Wilfred]

Regarding the compilation failure, I'm trying to cross-compile to ARM to reproduce the issue. . I've downloaded the .rlib files for rustc from RustBuild to ~/.multirust/toolchains/stable/lib/rustlib as documented in ruststrap.

I've also set up .cargo/config with:

[target.arm-unknown-linux-gnueabihf]
linker = "arm-none-eabi-gcc-5.3.0"

This is the ARM compiler on arch linux as far as I can see. I'm now getting linking errors:

/usr/lib/gcc/arm-none-eabi/5.3.0/../../../../arm-none-eabi/bin/ld: cannot find crt0.o: No such file or directory

Any ideas? Ideally we'd configure Travis to cross-compile too, to verify that the build isn't broken again in future.

[MagaTailor]

Yes, you have the linker but not the rest of the multilib/multarch stuff. The failure should still happen in rust, though.

[MagaTailor]

The libc crate is being added back cause others depend on it (tempfile needs 0.2) and anyway, where are you going to get your c_char, etc from?

Have a look here for a possible solution.

[MagaTailor]

It's not about bfc at all - it was caused by systemic breakage (called a fix) and there's no sign of a top-down solution.

For now I suggest we simply add another cast while investigating the alternative.