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[WebAssembly][lld] excessive undefined symbol errors when building a shared library #103592

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yamt opened this issue Aug 14, 2024 · 2 comments · May be fixed by #128223
Open

[WebAssembly][lld] excessive undefined symbol errors when building a shared library #103592

yamt opened this issue Aug 14, 2024 · 2 comments · May be fixed by #128223
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lld:wasm

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@yamt
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yamt commented Aug 14, 2024

after 22b7b84,
wasm-ld complains on undefined symbols when building -shared/-pie. it's nice.

however, it even complains on symbols which are expected to be provided/imported by wasm-ld itself. (eg. __heap_base)
i consider it a bug.

i saw it while buliding wasi-libc: WebAssembly/wasi-libc#526

a smaller recipe to reproduce: https://github.com/yamt/garbage/tree/master/wasm/ld-shared

with:

clang version 20.0.0git (https://github.com/llvm/llvm-project.git c31ac810910ac87531de636ea508abec6e29e8ff)

spacetanuki% ./test.sh

+ CC=/Volumes/PortableSSD/llvm/build/bin/clang
+ /Volumes/PortableSSD/llvm/build/bin/clang -o liba.so -nostdlib -shared -mexception-handling -fPIC -fvisibility=default -Wl,--no-entry a.c
wasm-ld: warning: creating shared libraries, with -shared, is not yet stable
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __heap_base
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __heap_end
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __cpp_exception
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __c_longjmp
clang: error: linker command failed with exit code 1 (use -v to see invocation)
@github-actions github-actions bot added the lld label Aug 14, 2024
yamt added a commit to yamt/wasi-libc that referenced this issue Aug 14, 2024
@yamt
mention llvm/llvm-project#103592
8513933
@yamt yamt mentioned this issue Aug 14, 2024
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llvmbot commented Aug 14, 2024

@llvm/issue-subscribers-lld-wasm

Author: YAMAMOTO Takashi (yamt)

after 22b7b84, wasm-ld complains on undefined symbols when building -shared/-pie. it's nice.

however, it even complains on symbols which are expected to be provided/imported by wasm-ld itself. (eg. __heap_base)
i consider it a bug.

i saw it while buliding wasi-libc: WebAssembly/wasi-libc#526

a smaller recipe to reproduce: https://github.com/yamt/garbage/tree/master/wasm/ld-shared

with:

clang version 20.0.0git (https://github.com/llvm/llvm-project.git c31ac810910ac87531de636ea508abec6e29e8ff)

spacetanuki% ./test.sh

+ CC=/Volumes/PortableSSD/llvm/build/bin/clang
+ /Volumes/PortableSSD/llvm/build/bin/clang -o liba.so -nostdlib -shared -mexception-handling -fPIC -fvisibility=default -Wl,--no-entry a.c
wasm-ld: warning: creating shared libraries, with -shared, is not yet stable
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __heap_base
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __heap_end
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __cpp_exception
wasm-ld: error: /var/folders/74/hw1sphgx0lv63q6pq_n5grw00000gn/T/a-7ab945.o: undefined symbol: __c_longjmp
clang: error: linker command failed with exit code 1 (use -v to see invocation)

@sbc100 sbc100 linked a pull request Feb 21, 2025 that will close this issue
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sbc100 commented Feb 21, 2025 •
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I have fix for the linker-generated symbols here: #128223

For __cpp_exception and __c_longjmp I think the idea is that they get defined some shared object such as libc.so or by the embedder. In emscripten the embedder provides them: https://github.com/emscripten-core/emscripten/blob/f7f639510c9f33d0aedf08a176d2f88b22259544/src/lib/libcore.js#L2201-L2207

sbc100 added a commit to sbc100/llvm-project that referenced this issue Feb 21, 2025
@sbc100
[lld][WebAssembly] Allow linker-synthetic symbols to be undefine when…
46ebbc2 
… building shared libraries

Fixes: llvm#103592
@CathalMullan CathalMullan mentioned this issue Mar 11, 2025
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