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[lld][WebAssembly] Work around limited architecture detection for wasm64 shared libraries #98961

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Jul 16, 2024
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[lld][WebAssembly] Work around limited architecture detection for wasm64 shared libraries #98961

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10 changes: 10 additions & 0 deletions lld/test/wasm/dylink.s
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,16 @@
# RUN: wasm-ld --experimental-pic -pie -o %t.wasm %t.o %t.lib.so
# RUN: obj2yaml %t.wasm | FileCheck %s

# Same again for wasm64

# RUN: llvm-mc -filetype=obj -triple=wasm64-unknown-emscripten -o %t.o %s
# RUN: llvm-mc -filetype=obj -triple=wasm64-unknown-emscripten %p/Inputs/ret32.s -o %t.ret32.o
# RUN: llvm-mc -filetype=obj -triple=wasm64-unknown-emscripten %p/Inputs/libsearch-dyn.s -o %t.dyn.o
# RUN: wasm-ld --experimental-pic -mwasm64 -shared %t.ret32.o %t.dyn.o -o %t.lib.so
# RUN: not wasm-ld --experimental-pic -mwasm64 -pie -o %t.wasm %t.o 2>&1 | FileCheck --check-prefix=ERROR %s
# RUN: wasm-ld --experimental-pic -mwasm64 -pie -o %t.wasm %t.o %t.lib.so
# RUN: obj2yaml %t.wasm | FileCheck %s

# ERROR: error: {{.*}}: undefined symbol: ret32
# ERROR: error: {{.*}}: undefined symbol: _bar
.functype ret32 (f32) -> (i32)
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8 changes: 6 additions & 2 deletions lld/wasm/InputFiles.cpp
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Expand Up @@ -408,6 +408,12 @@ ObjFile::ObjFile(MemoryBufferRef m, StringRef archiveName, bool lazy)
this->lazy = lazy;
this->archiveName = std::string(archiveName);

// Currently we only do this check for regular object file, and not for shared
// object files. This is because architecture detection for shared objects is
// currently based on a heuristic, which is fallable:
// https://github.com/llvm/llvm-project/issues/98778
checkArch(wasmObj->getArch());
Comment on lines +411 to +415
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Does this problem (that we cannot determine arch if there is no memory) only happen with shared objects? If so, why? If non-shared objects don't have a memory, how do we determine the arch?

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Yes, non-shared objects, produced by llvm always import the memory. We just get lucky that is the case.

In fact even shared object do, just not once they have been though wasm-opt, which will eliminate the memory completely if its unused.


// If this isn't part of an archive, it's eagerly linked, so mark it live.
if (archiveName.empty())
markLive();
Expand Down Expand Up @@ -456,8 +462,6 @@ WasmFileBase::WasmFileBase(Kind k, MemoryBufferRef m) : InputFile(k, m) {

bin.release();
wasmObj.reset(obj);

checkArch(obj->getArch());
}

void ObjFile::parse(bool ignoreComdats) {
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