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Fix LTO build #712

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Fix LTO build #712

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@alexcrichton alexcrichton commented Jan 13, 2026

  • Don't use LTO for startup objects
  • Put startup objects in the normal sysroot without LTO
  • Pass -flto in linker flags
  • Disable a test that fails with LTO enabled (unsure why)

@alexcrichton
Fix LTO build
118a2d5 
* Don't use LTO for startup objects
* Put startup objects in the normal sysroot without LTO
* Pass `-flto` in linker flags
* Disable a test that fails with LTO enabled (unsure why)
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alexcrichton commented Jan 13, 2026

This was discovered as part of WebAssembly/wasi-sdk#584 where the wasm-tools command run on startup objects failed because the startup objects weren't actually wasm, they're bitcode. I don't believe enabling LTO in this repository has ever worked for running tests, only for building. This attempts to get everything working. I did a bit of digging to figure out what's going wrong in the failing test, but in the end I have no idea why. It's probably some strict aliasing thing or something like that, so I've just disabled it for now.

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yamt commented Jan 13, 2026

This was discovered as part of WebAssembly/wasi-sdk#584 where the wasm-tools command run on startup objects failed because the startup objects weren't actually wasm, they're bitcode. I don't believe enabling LTO in this repository has ever worked for running tests, only for building. This attempts to get everything working. I did a bit of digging to figure out what's going wrong in the failing test, but in the end I have no idea why. It's probably some strict aliasing thing or something like that, so I've just disabled it for now.

is this something specific to p2/p3?

yamt
yamt reviewed Jan 13, 2026
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test/CMakeLists.txt
endif()
add_libc_test(functional/search_insque.c)
if (LTO STREQUAL "full")
set_tests_properties(libc_test_functional_search_insque.wasm PROPERTIES WILL_FAIL TRUE)
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can you add a link to a bug report?

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@alexcrichton alexcrichton Jan 13, 2026

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I don't have a bug report to link to. This repository does not control the source of this test, nor does this repository have WASI-specific source for insque and other functions. (I barely know what those functions are). If you'd like to open an issue I'd be happy to link it here.

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yamt commented Jan 13, 2026

Don't use LTO for startup objects

why?

Put startup objects in the normal sysroot without LTO

why?

Pass -flto in linker flags

this makes sense.

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alexcrichton commented Jan 13, 2026

Yes, startup objects are per-target. LTO is diasbles so the wasm-tools processing works. They're put in the normal sysroot because otherwise clang-19 locally didn't seem to find them.

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