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[lld][WebAssembly] Fix for --import-table when combined with reference types #97451

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Jul 2, 2024
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[lld][WebAssembly] Fix for --import-table when combined with reference types #97451

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26 changes: 26 additions & 0 deletions lld/test/wasm/import-table-explicit.s
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
# RUN: llvm-mc -mattr=+reference-types -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.o
# RUN: wasm-ld --import-table -o %t.wasm %t.o
# RUN: obj2yaml %t.wasm | FileCheck %s

.globl __indirect_function_table
.tabletype __indirect_function_table, funcref

.globl _start
_start:
.functype _start () -> ()
i32.const 1
call_indirect __indirect_function_table, () -> ()
end_function

# Verify the --import-table flag creates a table import

# CHECK: - Type: IMPORT
# CHECK-NEXT: Imports:
# CHECK-NEXT: - Module: env
# CHECK-NEXT: Field: __indirect_function_table
# CHECK-NEXT: Kind: TABLE
# CHECK-NEXT: Table:
# CHECK-NEXT: Index: 0
# CHECK-NEXT: ElemType: FUNCREF
# CHECK-NEXT: Limits:
# CHECK-NEXT: Minimum: 0x1
16 changes: 8 additions & 8 deletions lld/test/wasm/import-table.test → lld/test/wasm/import-table.s
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Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %p/Inputs/start.s -o %t.start.o
# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.o
# RUN: wasm-ld --export-all --import-table -o %t.wasm %t.start.o %t.o
# RUN: wasm-ld --export-all --import-table -o %t.wasm %t.o
# RUN: obj2yaml %t.wasm | FileCheck %s

.globl require_function_table
require_function_table:
.functype require_function_table () -> ()
i32.const 1
call_indirect () -> ()
end_function
.globl _start
_start:
.functype _start () -> ()
i32.const 1
# call_indirect instruction implicitly references the function table
call_indirect () -> ()
end_function

# Verify the --import-table flag creates a table import

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9 changes: 6 additions & 3 deletions lld/wasm/SymbolTable.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -681,10 +681,10 @@ TableSymbol *SymbolTable::createUndefinedIndirectFunctionTable(StringRef name) {
WasmTableType *type = make<WasmTableType>();
type->ElemType = ValType::FUNCREF;
type->Limits = limits;
StringRef module(defaultModule);
uint32_t flags = config->exportTable ? 0 : WASM_SYMBOL_VISIBILITY_HIDDEN;
flags |= WASM_SYMBOL_UNDEFINED;
Symbol *sym = addUndefinedTable(name, name, module, flags, nullptr, type);
Symbol *sym =
addUndefinedTable(name, name, defaultModule, flags, nullptr, type);
sym->markLive();
sym->forceExport = config->exportTable;
return cast<TableSymbol>(sym);
Expand Down Expand Up @@ -724,8 +724,11 @@ TableSymbol *SymbolTable::resolveIndirectFunctionTable(bool required) {
}

if (config->importTable) {
if (existing)
if (existing) {
existing->importModule = defaultModule;
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Is it possible to import a table from a non-default module? If so, how do we do it?

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Also, before this PR, what was this importModule set to?

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This function only deal with one very particular table (__indirect_function_table). This table is implicitly generated by the linker and we don't support defining it explicitly anywhere. The import name is also fixed. It should not be possible to attach any kind of custom import name to it.

existing->importName = functionTableName;
return cast<TableSymbol>(existing);
}
if (required)
return createUndefinedIndirectFunctionTable(functionTableName);
} else if ((existing && existing->isLive()) || config->exportTable ||
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