RUSTFLAGS breaks linker

[rva3]

RUSTFLAGS environment variable breaks linker , e.g RUSTFLAGS="-Ctarget-cpu=cortex-a55" x build --platform android --arch arm64 --format apk -r (happens on both master and release)

Log:

[1/3] Fetch precompiled artifacts
info: component 'rust-std' for target 'aarch64-linux-android' is up to date
[1/3] Fetch precompiled artifacts [177ms]
[2/3] Build rust `xtest`
   Compiling jni-sys v0.3.0
   Compiling bytes v1.10.1
   Compiling memchr v2.7.4
   Compiling log v0.4.27
   Compiling libc v0.2.172
   Compiling thiserror v1.0.69
   Compiling raw-window-handle v0.6.2
   Compiling bitflags v2.9.0
   Compiling cfg-if v1.0.0
   Compiling cesu8 v1.1.0
   Compiling pin-project-lite v0.2.16
   Compiling tracing-core v0.1.33
   Compiling ndk-context v0.1.1
   Compiling android-properties v0.2.2
   Compiling num_enum v0.7.3
   Compiling android-activity v0.6.0
   Compiling winit v0.30.10
   Compiling dpi v0.1.2
   Compiling smol_str v0.2.2
   Compiling ndk-sys v0.6.0+11769913
   Compiling cursor-icon v1.1.0
   Compiling tracing v0.1.41
   Compiling combine v4.6.7
   Compiling ndk v0.9.0
   Compiling jni v0.21.1
   Compiling xtest v0.1.0 (/home/user/projects/xtest)
warning: unused variable: `app`
 --> src/lib.rs:2:17
  |
2 | fn android_main(app: winit::platform::android::activity::AndroidApp) {
  |                 ^^^ help: if this is intentional, prefix it with an underscore: `_app`
  |
  = note: `#[warn(unused_variables)]` on by default

error: linking with `clang` failed: exit status: 1
  |
  = note:  "clang" "-Wl,--version-script=/tmp/rustcHNwBIP/list" "-Wl,--no-undefined-version" "/tmp/rustcHNwBIP/symbols.o" "<2 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "/home/user/projects/xtest/target/x/release/android/arm64/cargo/aarch64-linux-android/release/deps/{libwinit-2d0d06393b0532b2.rlib,libtracing-fa22f4f7a3c74579.rlib,libpin_project_lite-8c02c0c8121277bc.rlib,libtracing_core-b14b3c5b20e3b021.rlib,libandroid_activity-95d9d4acda35c272.rlib,libandroid_properties-86f90dd59382ac44.rlib,libndk_context-7afdd6d37142ed81.rlib,libjni-1870b546a7cddd7f.rlib,libcesu8-275e35db99e5f8e8.rlib,libcombine-6bc08c0f2216f6d7.rlib,libmemchr-fae525c0d294fe4e.rlib,libbytes-e232ddd7ba4cafd3.rlib,libndk-be97ebade109e8d1.rlib,libndk_sys-dd40e89905e0beea.rlib,liblog-01ff5d3cf4346918.rlib,libjni_sys-679338b93a9821e2.rlib,libthiserror-922c5551c6972e69.rlib,libnum_enum-f5a9aa2efb69bebe.rlib,liblibc-cd11e0bae91f144d.rlib,libbitflags-67ddfff8af95bb2b.rlib,libsmol_str-2db20c8117ecb1e5.rlib,libcursor_icon-49d01c142604477d.rlib,libdpi-09fd2f0da5cb9f48.rlib,libraw_window_handle-3831b38bb83ea891.rlib}.rlib" "<sysroot>/lib/rustlib/aarch64-linux-android/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,libcfg_if-*,liblibc-*,liballoc-*,librustc_std_workspace_core-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-landroid" "-ldl" "-llog" "-lunwind" "-ldl" "-lm" "-lc" "-L" "/tmp/rustcHNwBIP/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-o" "/home/user/projects/xtest/target/x/release/android/arm64/cargo/aarch64-linux-android/release/deps/libxtest.so" "-Wl,--gc-sections" "-shared" "-Wl,-z,relro,-z,now" "-Wl,-O1" "-Wl,--strip-debug" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: ld.lld: error: unable to find library -landroid
          ld.lld: error: unable to find library -llog
          clang: error: linker command failed with exit code 1 (use -v to see invocation)
          

warning: `xtest` (lib) generated 1 warning
error: could not compile `xtest` (lib) due to 1 previous error; 1 warning emitted

Steps to reproduce:

• cargo new xtest --lib
• cargo add winit --features android-native-activity
• src/lib.rs contents:

#[unsafe(no_mangle)]
fn android_main(app: winit::platform::android::activity::AndroidApp) {
    println!("test");
}

• Cargo.toml contents:

[package]
name = "xtest"
version = "0.1.0"
edition = "2024"

[lib]
crate-type = ["cdylib"]

[dependencies]
winit = { version = "0.30.10", features = ["android-native-activity"] }

x doctor output:

--------------------clang/llvm toolchain--------------------
clang                +pgo,               /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/clang
clang++              +pgo,               /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/clang++
llvm-ar              unknown             /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/llvm-ar
llvm-lib             unknown             /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/llvm-lib
llvm-readobj         20.0.0              /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/llvm-readobj
lld                  20.0.0              /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/lld
lld-link             20.0.0              /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/lld-link
lldb                 unknown             /home/user/Android/Sdk//ndk/29.0.13113456//toolchains/llvm/prebuilt/linux-x86_64/bin/lldb
lldb-server          unknown             /usr/bin/lldb-server

----------------------------rust----------------------------
rustup               1.28.2              /usr/bin/rustup
cargo                1.88.0-nightly      /usr/bin/cargo

--------------------------android---------------------------
adb                  1.0.41              /usr/bin/adb
javac                17.0.15             /usr/bin/javac
java                 17.0.15             /usr/bin/java
kotlin               not found
gradle               not found

[MarijnS95]

This might be because we set linker flags via CARGO_TARGET_<triple>_RUSTFLAGS, which has a lower precedence than your RUSTFLAGS resulting in this xbuild configuration being skipped:

xbuild/xbuild/src/cargo/mod.rs

Lines 301 to 303 in 5662af2

	self.add_link_arg(&format!("-B{}", sdk_lib_dir.display()));
	self.add_link_arg(&format!("-L{}", sdk_lib_dir.display()));
	self.add_link_arg(&format!("-L{}", lib_dir.display()));

xbuild/xbuild/src/cargo/mod.rs

Line 468 in 5662af2

self.cargo_target_env("RUSTFLAGS", &self.rust_flags.clone());

Realistically a few things should happen:

1. xbuild should read out RUSTFLAGS and error out with this useful guidance;
2. xbuild should read CARGO_TARGET_<triple>_RUSTFLAGS and merge its compiler configuration rather than overwriting it;
3. Now you should be able to set your target-specific flags via CARGO_TARGET_<triple>_RUSTFLAGS instead.

[rva3]

Thanks! I've added the following to .cargo/config.toml:

[target.aarch64-linux-android]
rustflags = ["-C", "target-cpu=cortex-a55"]

[MarijnS95]

Reopening because there is something for xbuild to improve here, otherwise we should re-close this as "not planned".

[shahn]

Should xbuild add to RUSTFLAGS instead of CARGO_TARGET_<triple>_RUSTFLAGS, iff RUSTFLAGS is set? At least for my usecase (setting -D warnings globally in CI) that would be preferable to unsetting the variable only for the xbuild build.