dtolnay/linkme

"The encapsulation symbol needs to be retained under --gc-sections properly"

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#49 opened on Jul 9, 2022

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Description

The current master branch fails to build on FreeBSD 14.0-CURRENT amd64, even though it still works on FreeBSD stable/13.

$ cargo test
...
  = note: ld: error: undefined symbol: __start_linkme_SHENANIGANS
          >>> referenced by x4z07wsgcl2z4i4
          >>>               /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::SHENANIGANS::hca25c6519cd4df0f)
          >>> the encapsulation symbol needs to be retained under --gc-sections properly; consider -z nostart-stop-gc (see https://lld.llvm.org/ELF/start-stop-gc)
          
          ld: error: undefined symbol: __stop_linkme_SHENANIGANS
          >>> referenced by x4z07wsgcl2z4i4
          >>>               /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::SHENANIGANS::hca25c6519cd4df0f)
          
          ld: error: undefined symbol: __start_linkme_EMPTY
          >>> referenced by x4z07wsgcl2z4i4
          >>>               /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_empty::EMPTY::h31c7f9e37773eb8f)
          >>> the encapsulation symbol needs to be retained under --gc-sections properly; consider -z nostart-stop-gc (see https://lld.llvm.org/ELF/start-stop-gc)
          
          ld: error: undefined symbol: __stop_linkme_EMPTY
          >>> referenced by x4z07wsgcl2z4i4
          >>>               /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_empty::EMPTY::h31c7f9e37773eb8f)
          
          ld: error: undefined symbol: __start_linkme_NONCOPY
          >>> referenced by x4z07wsgcl2z4i4
          >>>               /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_non_copy::NONCOPY::h920eb5b4a050a94d)
          >>> the encapsulation symbol needs to be retained under --gc-sections properly; consider -z nostart-stop-gc (see https://lld.llvm.org/ELF/start-stop-gc)
          
          ld: error: undefined symbol: __stop_linkme_NONCOPY
          >>> referenced by x4z07wsgcl2z4i4
          >>>               /usr/home/somers/src/rust/linkme/target/debug/deps/distributed_slice-425b465e5440679a.x4z07wsgcl2z4i4.rcgu.o:(distributed_slice::test_non_copy::NONCOPY::h920eb5b4a050a94d)
          cc: error: linker command failed with exit code 1 (use -v to see invocation)
          

error: could not compile `linkme` due to previous error
error: could not compile `linkme` due to previous error
error: could not compile `linkme` due to previous error

Contributor guide

Research direction
Investigate the linker error on FreeBSD 14.0 CURRENT. The error indicates that encapsulation symbols start linkme * and stop linkme * are undefined when gc sections is used. According to the LLVM documentation, this can be resolved by adding z nostart stop gc to the linker flags. Look into the Rust build configuration (e.g., .cargo/config.toml) or the crate's build.rs to apply this flag conditionally for FreeBSD. Alternatively, explore whether the crate's approach to defining these symbols needs adjustment for the new linker behavior.
Tech stack
rust
Domain
build system
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Rust
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70