How do I fix "ld: error: unable to find library -lgcc" when cross-compiling rust to android? - linux

Question

I'm trying to get rust working on android. However, when I try to cross-compile to android I get the following linking error:
$ cargo build --target=arm-linux-androideabi
Compiling <project> v0.1.0 (<project>)
error: linking with `/opt/android-sdk/ndk/23.0.7599858/toolchains/llvm/prebuilt/linux-x86_64/bin/armv7a-linux-androideabi31-clang` failed: exit status: 1
(very long toolchain command from cargo)
ld: error: unable to find library -lgcc
clang-12: error: linker command failed with exit code 1 (use -v to see invocation)
I have installed the ndk and changed the linker in .cargo/config to the android clang linker. I also tried the standalone toolchains with the same result. The guide I used was the following: https://mozilla.github.io/firefox-browser-architecture/experiments/2017-09-21-rust-on-android.html
Cross-compilation does work when using crate-type = ["rlib"] instead of crate-type = ["cdylib"], but I need an .so file not an .rlib file.
In case it's relevant, i'm using Manjaro Linux.

Answer 1

UPDATE:
I found the following pull request: https://github.com/rust-lang/rust/pull/85806 After switching to ndk22 it worked. I havn't tried if the pull request fixes the issue (probably does).

Answer 2

Without switching to an older NDK version, I found using the workaround provided by ssrlive to work for me. Here's their comment:
Fixing build error for NDK 23 and above
find out all the 4 folders containing file libunwind.a, in my PC,
it's
C:\Users\Administrator\AppData\Local\Android\Sdk\ndk\23.1.7779620\toolchains\llvm\prebuilt\windows-x86_64\lib64\clang\12.0.8\lib\linux\x86_64\
and more. create 4 text files named libgcc.a in the same folders
with this contents
INPUT(-lunwind)
reference
link
In macOS, the paths are
~/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/14.0.1/lib/linux/i386/libunwind.a
~/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/14.0.1/lib/linux/arm/libunwind.a
~/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/14.0.1/lib/linux/aarch64/libunwind.a
~/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/14.0.1/lib/linux/x86_64/libunwind.a
In Linux, the paths are
~/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/14.0.1/lib/linux/i386/libunwind.a
~/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/14.0.1/lib/linux/aarch64/libunwind.a
~/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/14.0.1/lib/linux/x86_64/libunwind.a
~/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/14.0.1/lib/linux/arm/libunwind.a
In Windows, the paths are
~/AppData/Local/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/windows-x86_64/lib64/clang/14.0.1/lib/linux/aarch64/libunwind.a
~/AppData/Local/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/windows-x86_64/lib64/clang/14.0.1/lib/linux/arm/libunwind.a
~/AppData/Local/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/windows-x86_64/lib64/clang/14.0.1/lib/linux/i386/libunwind.a
~/AppData/Local/Android/Sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/windows-x86_64/lib64/clang/14.0.1/lib/linux/x86_64/libunwind.a
create file command in Linux/macOS
cat << EOF > libgcc.a
INPUT(-lunwind)
EOF
This is of course extremely brittle and not the "right" solution, but the workaround works fine as of 2022-10-12 with ndk version 25.1.8937393.