Use bulk libunwind section registration when available - #14304
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Register and deregister whole .eh_frame sections with libunwind when both section APIs are available. Remember the registration mode for matching cleanup, and retain individual-FDE registration as the fallback. The libgcc path continues using its existing whole-section interface. On macOS, resolve the optional APIs at runtime from the library supplying the linked frame API. Verify the registration and deregistration identities and restrict lookup to that image so custom unwinders cannot mix registries. Cache the matched pair while allowing builds against older macOS SDKs. Add native registry lifecycle and x86-64 stack-walking tests on macOS and Linux, controlled API-availability and provider-mismatch tests, and a linked-provider fixture that exercises the real macOS loader.
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I encountered performance issues when working with large Wasm modules similar to those described in issue #6541. That issue led to a configuration fix making it possible to opt out of native unwinding on macOS.
However,
libunwindprovides whole-section APIs that Wasmtime currently doesn’t use:__unw_add_dynamic_eh_frame_sectionand__unw_remove_dynamic_eh_frame_section. These allow registering full.eh_framesections rather than registering each frame description entry (FDE) individually.Testing against my large Wasm module, I measured the following median total process wall times, including teardown. Most of the improvement comes from teardown after the workload finishes.
For the x86-64 Linux measurements, I explicitly selected LLVM
libunwindinstead of the machine’s defaultlibgcc. LLVMlibunwindis also used by configurations such as Rust’s default static musl builds, Chimera Linux, and Gentoo’s LLVM profiles. The existinglibgccregistration path is unchanged.This PR checks whether both batch registration APIs are available and uses them when they are, falling back to the existing APIs otherwise.
The
native_unwind_walks_nested_wasm_framestest currently runs on x86-64 macOS and Linux. Developing it exposed an existing native stack-walking bug on ARM64 macOS, addressed in #14303. Once that fix lands, I can enable the test on ARM64 macOS as well.