Cargo panics on Arch Linux when compiling on exFAT partition

Cargo version

cargo 1.86.0 (adf9b6ad1 2025-02-28)

Problem

Whenever I try to cargo run or cargo build a project on my exFAT partition on Arch Linux, it fails with the following error:

   Compiling test-crate v0.1.0 (/run/mount/Data/test-crate)
warning: error copying object file `/run/mount/Data/test-crate/target/debug/deps/test_crate-171d3f4b5eb94014.1844j56bgs10zwdjmbmp4ewcl.rcgu.o` to incremental directory as `/run/mount/Data/test-crate/target/debug/incremental/test_crate-1cwjhrbi82tge/s-h75ofrd5kj-040rlag-working/1844j56bgs10zwdjmbmp4ewcl.o`: Operation not permitted (os error 1)

warning: error copying object file `/run/mount/Data/test-crate/target/debug/deps/test_crate-171d3f4b5eb94014.1xv4e2iaijt2221ugfejfkj9p.rcgu.o` to incremental directory as `/run/mount/Data/test-crate/target/debug/incremental/test_crate-1cwjhrbi82tge/s-h75ofrd5kj-040rlag-working/1xv4e2iaijt2221ugfejfkj9p.o`: Operation not permitted (os error 1)

warning: error copying object file `/run/mount/Data/test-crate/target/debug/deps/test_crate-171d3f4b5eb94014.6p6gfwaw87bt5ts5a6awdvy49.rcgu.o` to incremental directory as `/run/mount/Data/test-crate/target/debug/incremental/test_crate-1cwjhrbi82tge/s-h75ofrd5kj-040rlag-working/6p6gfwaw87bt5ts5a6awdvy49.o`: Operation not permitted (os error 1)

warning: error copying object file `/run/mount/Data/test-crate/target/debug/deps/test_crate-171d3f4b5eb94014.6q31c3ffz1ao19rvlsb4tomhl.rcgu.o` to incremental directory as `/run/mount/Data/test-crate/target/debug/incremental/test_crate-1cwjhrbi82tge/s-h75ofrd5kj-040rlag-working/6q31c3ffz1ao19rvlsb4tomhl.o`: Operation not permitted (os error 1)

warning: error copying object file `/run/mount/Data/test-crate/target/debug/deps/test_crate-171d3f4b5eb94014.8wg0ifnylxkm8sglnzmusehrx.rcgu.o` to incremental directory as `/run/mount/Data/test-crate/target/debug/incremental/test_crate-1cwjhrbi82tge/s-h75ofrd5kj-040rlag-working/8wg0ifnylxkm8sglnzmusehrx.o`: Operation not permitted (os error 1)

warning: error copying object file `/run/mount/Data/test-crate/target/debug/deps/test_crate-171d3f4b5eb94014.9edjogq1wwbwf6yxpzh8o80lw.rcgu.o` to incremental directory as `/run/mount/Data/test-crate/target/debug/incremental/test_crate-1cwjhrbi82tge/s-h75ofrd5kj-040rlag-working/9edjogq1wwbwf6yxpzh8o80lw.o`: Operation not permitted (os error 1)

warning: `test-crate` (bin "test-crate") generated 6 warnings
error: failed to link or copy `/run/mount/Data/test-crate/target/debug/deps/test_crate-171d3f4b5eb94014` to `/run/mount/Data/test-crate/target/debug/test-crate`

Caused by:
  Operation not permitted (os error 1)

Running with root permissions
When I use sudo cargo run (and the project has more files than the default main.rs), it panics like this:

   Compiling test-crate v0.1.0 (/run/mount/Data/test-crate)
warning: hard linking files in the incremental compilation cache failed. copying files instead. consider moving the cache directory to a file system which supports hard linking in session dir `/run/mount/Data/test-crate/target/debug/incremental/test_crate-3aiikf0zz4qco/s-h75olu36wq-0bx3gll-working`

error: cached cgu 3jc4qbatsnqtmfg9qzi0sbrfc should have an object file, but doesn't


thread 'coordinator' panicked at /usr/src/debug/rust/rustc-1.86.0-src/compiler/rustc_codegen_ssa/src/back/write.rs:1680:29:
/usr/src/debug/rust/rustc-1.86.0-src/compiler/rustc_codegen_ssa/src/back/write.rs:1680:29: worker thread panicked
stack backtrace:
   0:     0x7cd9e10dd6b0 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h1a61e653684797d4
   1:     0x7cd9e112c6e3 - core::fmt::write::hef3878caa31fc074
   2:     0x7cd9e10d1db3 - <unknown>
   3:     0x7cd9e10dd502 - <unknown>
   4:     0x7cd9e10dfabf - <unknown>
   5:     0x7cd9e10df92a - std::panicking::default_hook::hf5b5ddbe229b04b3
   6:     0x7cd9dddd059d - <unknown>
   7:     0x7cd9e10e05f3 - std::panicking::rust_panic_with_hook::h85e74030df1c120f
   8:     0x7cd9e0b29ce5 - <unknown>
   9:     0x7cd9e0b231d9 - std[425a963a3e5d7a57]::sys::backtrace::__rust_end_short_backtrace::<std[425a963a3e5d7a57]::panicking::begin_panic<alloc[4540294945132585]::string::String>::{closure#0}, !>
  10:     0x7cd9e0a25cbd - std[425a963a3e5d7a57]::panicking::begin_panic::<alloc[4540294945132585]::string::String>
  11:     0x7cd9e0baf799 - <unknown>
  12:     0x7cd9e0ba866f - <unknown>
  13:     0x7cd9e0ba862e - <unknown>
  14:     0x7cd9e0baf6b3 - rustc_middle[a294d822c310247b]::util::bug::bug_fmt
  15:     0x7cd9de16fd5e - std[425a963a3e5d7a57]::sys::backtrace::__rust_begin_short_backtrace::<<rustc_codegen_llvm[ac121063ebf01a90]::LlvmCodegenBackend as rustc_codegen_ssa[2746cc10987e5ed]::traits::backend::ExtraBackendMethods>::spawn_named_thread<rustc_codegen_ssa[2746cc10987e5ed]::back::write::start_executing_work<rustc_codegen_llvm[ac121063ebf01a90]::LlvmCodegenBackend>::{closure#5}, core[f10772f7cf65ba1b]::result::Result<rustc_codegen_ssa[2746cc10987e5ed]::back::write::CompiledModules, ()>>::{closure#0}, core[f10772f7cf65ba1b]::result::Result<rustc_codegen_ssa[2746cc10987e5ed]::back::write::CompiledModules, ()>>
  16:     0x7cd9de08857c - <unknown>
  17:     0x7cd9e10e9cab - <unknown>
  18:     0x7cd9dc6a370a - <unknown>
  19:     0x7cd9dc727aac - <unknown>
  20:                0x0 - <unknown>

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.86.0 (05f9846f8 2025-03-31) (Arch Linux rust 1:1.86.0-1) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
warning: `test-crate` (lib) generated 1 warning
error: could not compile `test-crate` (lib) due to 1 previous error; 1 warning emitted

My system:

This only happens on my exFAT partition, not on the normal linux partition. It's mounted like this in the fstab:

LABEL=Data              /run/mount/Data exfat           rw,relatime,fmask=0000,dmask=0000

Every file has rwxrwxrwx permissions. Also, I'm able to build and run projects on that partition using my windows installation.

How to reproduce

I have no idea if you are able to reproduce it like this, but maybe give it a try:

• Use arch linux
• Get yourself an exFAT partition, and add it to the fstab with a 0000 mask and mountpoint somewhere under /run
• cd into the partition and create a new crate using cargo new
• create an empty lib.rs file in the src directory
• Go sudo cargo run and you should get the error

Stackoverflow post

Here's the link to a stackoverflow post where I asked about this:
https://stackoverflow.com/questions/79612554/cargo-says-operation-not-permitted-when-compiling-on-arch-linux

Reproduce the failure with Cargo on an Arch Linux exFAT mount using the fstab options and crate steps in the report. Start at rustc_codegen_ssa/src/back/write.rs:1680 and inspect the incremental compilation path after the hard-link fallback; compare cargo run/build behavior on exFAT and a normal Linux filesystem. Done means the same setup no longer causes a compiler panic and reports the failure safely.