Call clang directly when cross-compiling from Windows to Android

[maxded]

On Windows, the Android clang compiler is provided as a .cmd file instead of a .exe file. The .cmd file is spawned as a process and thus has a command-line limit of around 32000 characters, which you will most likely not reach. However, the .cmd launches the clang.exe, which results in a command-line limit of around 8200 characters, which larger projects with lots of include directories will easily reach.

As a fix, I've reintroduced response files when compiling from Windows to Android.

[alexcrichton]

Thanks for the PR!

I was hoping it wouldn't come to this though since response files were just removed in #564. Is there any way to reasonably shorten the command line for your project? Or perhaps consider this a bug for Android that we can spawn the process but it can't spawn a subprocess?

[maxded]

Good point! Was unsure myself whos responsibility this was to "fix". As shortening the command line for my project is not possible I've come up with a second, better, solution.

All the .cmd files do on Windows is call the main clang binary with the proper --target argument. As all that data is known to us we can construct this ourselves and call the main clang binary directly. :)

[alexcrichton]

Seems like a nice strategy if we can get it to work! I think though that one of the purposes of #495 is that the wrapper scripts pass a different --target than rustc, and that's intentional for the compilation of the C code?

[maxded]

Yes they do pass a different --target, which instead of having the shell script pass it, I construct the proper --target myself and call clang directly.

A call to the aarch64-linux-android21-clang.cmd shell script internally calls clang.exe with --target=aarch64-linux-android21. Basically, the proper target and clang "version" (clang or clang++) is in the .cmd file name. So by extracting those ourselves we can call clang.exe or clang++.exe directly.

On Windows, I've checked all .cmd files and being able to extract the the proper --target is true for all of them! The i686-linux-android16 to 24 .cmd files also add the -mstackrealign argument, which I've done as well.

So unless I'm misunderstanding or missing something I think we're good to go. :)

[alexcrichton]

I think the inner closure should be ok here to remove, it's fine to just have one if let for the file_name binding and avoid the closure business.

[alexcrichton]

Is this what the current scripts do? Is there a reason to perhaps not pass this unconditionally? (I have no idea what this flag does)

[maxded]

Yea that's what the scripts do. Only the i686-linux-android16-23 have the -mstackrealign option added in the script, which force realigns the stack at entry of every function. Don't think we want to do that unconditionally as I am not sure what the flag does as well.

[alexcrichton]

Hm ok, can you add a comment for why this arg is added? Also, is 23 the latest version? Or do newer versions not require this argument?

[maxded]

Newer versions do not require the arguments

[alexcrichton]

Hm ok, in that case could this perhaps be tweaked a bit differently to instead of looping over versions to instead take a look at the target and try to parse a version at the end? If this no longer happens then this is basically just handling older historical compilers then.

[maxded]

Done!

[alexcrichton]

👍

Thanks again!

[suqiernb]

// build.rs
extern crate cc;

fn main() {
    let mut build = cc::Build::new();
    let tool = build.get_compiler();
    println!("{:#?}", tool);
    build.file("src/core.c")
        .compile("core");
}

D:\XXX\demo>cargo build --release --target i686-linux-android
   Compiling demo v0.1.0 (D:\Development\WorkSpace\clion\rust\study\demo)
error: failed to run custom build command for `demo v0.1.0 (D:XXX\demo)`

Caused by:
  process didn't exit successfully: `D:\XXX\demo\target\release\build\demo-eaac7e9af5279e16\build-s
cript-build` (exit code: 1)
  --- stdout
  OPT_LEVEL = Some("3")
  TARGET = Some("i686-linux-android")
  HOST = Some("x86_64-pc-windows-msvc")
  CC_i686-linux-android = None
  CC_i686_linux_android = None
  TARGET_CC = None
  CC = None
  CFLAGS_i686-linux-android = None
  CFLAGS_i686_linux_android = None
  TARGET_CFLAGS = None
  CFLAGS = None
  CRATE_CC_NO_DEFAULTS = None
  DEBUG = Some("false")
  Tool {
      path: "clang.exe",
      cc_wrapper_path: None,
      cc_wrapper_args: [],
      args: [
          "--target=i686-linux-android",
          "-O3",
          "-DANDROID",
          "-ffunction-sections",
          "-fdata-sections",
          "-fPIC",
          "--target=i686-linux-android",
          "-Wall",
          "-Wextra",
      ],
      env: [],
      family: Clang,
      cuda: false,
      removed_args: [],
  }
  running: "clang.exe" "--target=i686-linux-android" "-O3" "-DANDROID" "-ffunction-sections" "-fdata-sections" "-fPIC" "--target=i686-linux-android" "-Wall" "-Wextra" "-o" "D:XXX\\demo\\target\\i686-linux-android\\release\\build\\demo-0d1113bc106cefdd\\out\\src/ffi/core.o" "-c" "src/ffi/core.c"

  --- stderr


  error occurred: Failed to find tool. Is `clang.exe` installed? (see https://github.com/alexcrichton/cc-rs#compile-time-requirements for help)