Failed to compile libunwind

[iulianR]

Hello!

With the following config:

$ cat .cargo/config
[target.aarch64-unknown-linux-musl]
linker = "aarch64-openwrt-linux-musl-gcc"
rustflags = [
    "-C", "target-feature=-crt-static",
    "-C", "prefer-dynamic",
    "-C", "link_arg=-lgcc",
    "-C", "link_arg=-s",
    "-L/opt/toolchain/sdk-aarch64-gcc7-musl/staging_dir/toolchain-aarch64_cortex-a72_gcc-7.3.0_musl/lib64/",
    "-L/opt/toolchain/sdk-aarch64-gcc7-musl/staging_dir/target-aarch64_cortex-a72_musl/usr/lib",
]

This in $PATH:

$ echo $PATH
/opt/toolchain/sdk-aarch64-gcc7-musl/staging_dir/toolchain-aarch64_cortex-a72_gcc-7.3.0_musl/bin:<...>

With the directory containing:

$ ls /opt/toolchain/sdk-aarch64-gcc7-musl/staging_dir/toolchain-aarch64_cortex-a72_gcc-7.3.0_musl/bin | grep aarch64-openwrt-linux-musl-gcc
aarch64-openwrt-linux-musl-gcc
aarch64-openwrt-linux-musl-gcc-7.3.0
aarch64-openwrt-linux-musl-gcc-ar
aarch64-openwrt-linux-musl-gcc-nm
aarch64-openwrt-linux-musl-gcc-ranlib

Cargo.toml:

[profile.dev]
panic = "abort"

[profile.release]
panic = "abort"

Xargo.toml:

[dependencies]
std = {}

This command fails:

$ xargo build --release --target aarch64-unknown-linux-musl
   Compiling unwind v0.0.0 (/home/master/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libunwind)
error: failed to run custom build command for `unwind v0.0.0 (/home/master/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libunwind)`

Caused by:
  process didn't exit successfully: `/tmp/xargo.Q543O70KJ1oj/target/release/build/unwind-080da0be54a1605a/build-script-build` (exit code: 1)
--- stdout
cargo:rerun-if-changed=build.rs
cargo:rustc-link-search=native=/tmp/xargo.Q543O70KJ1oj/target/aarch64-unknown-linux-musl/release/build/unwind-a98e36b91a645d82/out
running: "aarch64-linux-musl-gcc" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-I" "../llvm-project/libunwind/include" "-std=c99" "-std=c++11" "-nostdinc++" "-fno-exceptions" "-fno-rtti" "-fstrict-aliasing" "-funwind-tables" "-D__LITTLE_ENDIAN__=1" "-o" "/tmp/xargo.Q543O70KJ1oj/target/aarch64-unknown-linux-musl/release/build/unwind-a98e36b91a645d82/out/../llvm-project/libunwind/src/Unwind-EHABI.o" "-c" "../llvm-project/libunwind/src/Unwind-EHABI.cpp"

--- stderr

error occurred: Failed to find tool. Is `aarch64-linux-musl-gcc` installed?

Anyone has any idea? I can't figure it out where the problem comes from.

[RalfJung]

libstd has an unconditional dependency on libunwind. But building libunwind seems to fail because you don't have aarch64-linux-musl-gcc which it requires for cross-building. You seem to have aarch64-openwrt-linux-musl-gcc, but well, that's not the same thing.

I'm afraid I have no experience cross-building for such platforms, so that is about all I can tell you...

[iulianR]

Oops, I ended up pasting the wrong error (one where the linker was not in PATH) while trying to prepare a minimal setup. Here is the error that I'm getting:

error: failed to run custom build command for `unwind v0.0.0 (/home/master/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libunwind)`
Caused by:
  process didn't exit successfully: `/tmp/xargo.C5ty0ZI1mUUm/target/release/build/unwind-080da0be54a1605a/build-script-build` (exit code: 1)
--- stdout
cargo:rerun-if-changed=build.rs
cargo:rustc-link-search=native=/tmp/xargo.C5ty0ZI1mUUm/target/aarch64-unknown-linux-musl/release/build/unwind-a98e36b91a645d82/out
running: "aarch64-openwrt-linux-musl-gcc" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-I" "../llvm-project/libunwind/include" "-std=c99" "-std=c++11" "-nostdinc++" "-fno-exceptions" "-fno-rtti" "-fstrict-aliasing" "-funwind-tables" "-D__LITTLE_ENDIAN__=1" "-o" "/tmp/xargo.C5ty0ZI1mUUm/target/aarch64-unknown-linux-musl/release/build/unwind-a98e36b91a645d82/out/../llvm-project/libunwind/src/Unwind-EHABI.o" "-c" "../llvm-project/libunwind/src/Unwind-EHABI.cpp"
cargo:warning=aarch64-openwrt-linux-musl-gcc: error: ../llvm-project/libunwind/src/Unwind-EHABI.cpp: No such file or directory
cargo:warning=aarch64-openwrt-linux-musl-gcc: fatal error: no input files
cargo:warning=compilation terminated.
exit code: 1
--- stderr
error occurred: Command "aarch64-openwrt-linux-musl-gcc" "-O3" "-ffunction-sections" "-fdata-sections" "-fPIC" "-I" "../llvm-project/libunwind/include" "-std=c99" "-std=c++11" "-nostdinc++" "-fno-exceptions" "-fno-rtti" "-fstrict-aliasing" "-funwind-tables" "-D__LITTLE_ENDIAN__=1" "-o" "/tmp/xargo.C5ty0ZI1mUUm/target/aarch64-unknown-linux-musl/release/build/unwind-a98e36b91a645d82/out/../llvm-project/libunwind/src/Unwind-EHABI.o" "-c" "../llvm-project/libunwind/src/Unwind-EHABI.cpp" with args "aarch64-openwrt-linux-musl-gcc" did not execute successfully (status code exit code: 1).

It seems that path ../llvm-project/libunwind/src/Unwind-EHABI.cpp does not exist. I replaced the compiler path with a bash script that does ls .. and the llvm-project directory does not seem to exist:

total 52
drwxr-xr-x.  2 master master 4096 Mar  9 12:06 build_helper
drwxr-xr-x. 10 master master 4096 Mar  9 12:06 liballoc
drwxr-xr-x. 22 master master 4096 Mar  9 12:06 libcore
drwxr-xr-x.  2 master master 4096 Mar  9 12:06 libpanic_abort
drwxr-xr-x.  3 master master 4096 Mar  9 12:06 libpanic_unwind
drwxr-xr-x.  3 master master 4096 Mar  9 12:06 libproc_macro
drwxr-xr-x.  2 master master 4096 Mar  9 12:06 libprofiler_builtins
drwxr-xr-x. 14 master master 4096 Mar  9 12:06 libstd
drwxr-xr-x.  3 master master 4096 Mar  9 12:06 libterm
drwxr-xr-x.  5 master master 4096 Mar  9 12:06 libtest
drwxr-xr-x.  2 master master 4096 Mar  9 12:06 libunwind
drwxr-xr-x.  6 master master 4096 Mar  9 12:06 stdarch
drwxr-xr-x.  5 master master 4096 Mar  9 12:06 tools

This is what led me to believe that it's not a problem related to the compiler. rust-src and rustc seem up to date.

$ rustup component add rust-src                            
info: component 'rust-src' is up to date

$ rustc -V                     
rustc 1.43.0-nightly (564758c4c 2020-03-08)

Any idea what I should investigate next? I did manage to compile in the same manner some months ago, so it might be something that changed in Rust or Xargo since then.

[RalfJung]

The rustc src directory contains llvm-project... so it looks like some change in rustc's libunwind made that depend on the LLVM checkout, and therefore rust-src is not self-contained any more.

Looking at the libunwind build script, LLVM libunwind is always used for Linux musl targets. That behavior got introduced by https://github.com/rust-lang/rust/pull/63173, so I would guess that PR broke xargo for such targets.

[RalfJung]

That said, it looks like before it relied on libunwind.a being available somehow, and it is not clear how you got that file either.

[iulianR]

That said, it looks like before it relied on libunwind.a being available somehow, and it is not clear how you got that file either.

It probably comes from -L/opt/toolchain/sdk-aarch64-gcc7-musl/staging_dir/target-aarch64_cortex-a72_musl/usr/lib as my toolchain contains libunwind.a compiled for aarch64 musl.

[iulianR]

The rustc src directory contains llvm-project... so it looks like some change in rustc's libunwind made that depend on the LLVM checkout, and therefore rust-src is not self-contained any more.

Then this is mostly a problem of the rust-src component in rustup?

[RalfJung]

Well... either rust-src should contain llvm-project/libunwind, or else the libunwind build.rs should be smart enough to pick up the libunwind.a that is present on your system.

[iulianR]

For now I was able to progress by cloning llvm-project in the rust/src directory, but this not ideal. If I have time, I will try to see if this issue is already reported somewhere in rustup or in rust.

[RalfJung]

rustup just installs archives created by rust, so that would be the right repo to report in. Probably the solution is to add src/llvm-project/libunwind in this list, but I am not sure.

[iulianR]

Ok, unless you want to (as you have more experience with the process), I will report this issue in rustup. Thanks for help!

[RalfJung]

The issue should go to rust, not rustup. :)

You know all the actual details of what you want to do so it is probably better if you report it. Feel free to reference the discussion here.

EDIT: Ah, you already did.

[iulianR]

The issue should go to rust, not rustup. :)

Right, I was under the impression that the list is actually maintained by rustup and I didn't pay attention. I assume you talked with someone to move the issue, so thanks for that.

[RalfJung]

They moved the issue without my intervention, but anyway it is in the right place now. ;)