Bug: the static perf variant fails to link on Linux (undefined __atomic_compare_exchange) #38

Ladybug version: lbug crate from main with engine v0.20.4 (LBUG_VERSION=0.20.4). I first hit it with the 0.19.1 crate and engine v0.20.0, and it has been the same on every release since.

OS: Ubuntu 24.04.5 LTS, x86_64. Also reproduces on aarch64.

What happened?

Setting LBUG_LINUX_VARIANT=perf makes the final link fail:

/usr/bin/ld: liblbug.a(buffer_manager.cpp.o): in function
  `lbug::storage::EvictionQueue::insert(unsigned int, unsigned int)':
  buffer_manager.cpp:(.text+0x66): undefined reference to `__atomic_compare_exchange'
  ... also in EvictionQueue::clear, EvictionQueue::tryClear,
      BufferManager::pin, BufferManager::evictPages
collect2: error: ld returned 1 exit status

The perf archive has an undefined reference to __atomic_compare_exchange, and the compat archive doesn't. Same on both architectures in v0.20.4:

nm -u liblbug.a | grep -c '__atomic_compare_exchange$'
  x86_64 compat: 0    x86_64 perf: 1
  aarch64 compat: 0   aarch64 perf: 1

It comes from the 16-byte atomics in the buffer manager's eviction queue, which GCC turns into libatomic calls. build.rs links stdc++, ssl and crypto but not atomic, so nothing provides the symbol. Compat is the default, which is probably why nobody has run into it.

I expected the perf variant to link the same way compat does.

Steps to reproduce

1. On Linux, from a clean build directory, depend on lbug and build with the perf variant: LBUG_VERSION=0.20.4 LBUG_LINUX_VARIANT=perf cargo build --release.
2. The link fails with the error above.

Fix

I've opened #39, which links libatomic next to libstdc++ on Linux static builds. Rust passes --as-needed to the linker, so compat binaries don't pick up a new runtime dependency; their NEEDED list is identical before and after. Happy to change it if you'd rather fix it on the engine side.