[WebAssembly][Object]Use file offset as function symbol address for linked files (#76198)
WebAssembly doesn't have a single virtual memory space the way other object formats or architectures do, so "addresses" mean different things depending on the context. Function symbol addresses in object files are offsets from the start of the code section. This is good for linking and relocation. However when dealing with linked binaries, offsets from the start of the file/module are more often used (e.g. for stack traces in browsers), and are more useful for use cases like binary size attribution. This PR changes Object to use the file offset instead of the section offset for function symbols, but only for linked (non-DSO) files. This implements item number 4 from #76107
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Derek Schuff authored and 
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@@ -1667,10 +1667,18 @@ Expected<StringRef> WasmObjectFile::getSymbolName(DataRefImpl Symb) const {
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Expected<uint64_t> WasmObjectFile::getSymbolAddress(DataRefImpl Symb) const {
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auto &Sym = getWasmSymbol(Symb);
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if (Sym.Info.Kind == wasm::WASM_SYMBOL_TYPE_FUNCTION &&
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isDefinedFunctionIndex(Sym.Info.ElementIndex))
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return getDefinedFunction(Sym.Info.ElementIndex).CodeSectionOffset;
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else
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return getSymbolValue(Symb);
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isDefinedFunctionIndex(Sym.Info.ElementIndex)) {
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// For object files, use the section offset. The linker relies on this.
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// For linked files, use the file offset. This behavior matches the way
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// browsers print stack traces and is useful for binary size analysis.
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// (see https://webassembly.github.io/spec/web-api/index.html#conventions)
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uint32_t Adjustment = isRelocatableObject() || isSharedObject()
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? 0
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: Sections[CodeSection].Offset;
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return getDefinedFunction(Sym.Info.ElementIndex).CodeSectionOffset +
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Adjustment;
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}
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return getSymbolValue(Symb);
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}
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uint64_t WasmObjectFile::getWasmSymbolValue(const WasmSymbol &Sym) const {
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@@ -0,0 +1,74 @@
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# RUN: yaml2obj %s -o %t.wasm
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# RUN: llvm-nm %t.wasm | FileCheck %s
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# CHECK: 0000009f T my_func_export
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# CHECK-NEXT: 0000002a D my_global_export
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# CHECK-NEXT: 00000000 D my_table_export
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--- !WASM
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FileHeader:
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Version: 0x1
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Sections:
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- Type: TYPE
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Signatures:
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- Index: 0
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ParamTypes: []
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ReturnTypes: []
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- Type: IMPORT
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Imports:
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- Module: env
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Field: foo
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Kind: FUNCTION
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SigIndex: 0
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- Module: env
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Field: bar
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Kind: GLOBAL
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GlobalType: I32
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GlobalMutable: true
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- Module: env
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Field: memory
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Kind: MEMORY
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Memory:
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Minimum: 0x1
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- Type: FUNCTION
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FunctionTypes: [ 0 ]
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- Type: TABLE
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Tables:
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- Index: 0
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ElemType: FUNCREF
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Limits:
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Flags: [ HAS_MAX ]
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Minimum: 0x1
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Maximum: 0x1
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- Type: GLOBAL
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Globals:
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- Index: 1
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Mutable: false
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Type: I32
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InitExpr:
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Opcode: I32_CONST
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Value: 42
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- Type: EXPORT
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Exports:
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- Name: my_func_export
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Kind: FUNCTION
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Index: 1
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- Name: my_global_export
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Kind: GLOBAL
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Index: 1
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- Name: my_table_export
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Kind: TABLE
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Index: 0
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- Type: CODE
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Functions:
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- Index: 1
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Locals:
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Body: 00
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- Type: DATA
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Segments:
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- SectionOffset: 0
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InitFlags: 0
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Offset:
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Opcode: I32_CONST
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Value: 0
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Content: ''
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@@ -0,0 +1,75 @@
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# RUN: yaml2obj %s -o %t.wasm
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# RUN: llvm-objdump -t %t.wasm | FileCheck %s
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#
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# CHECK: SYMBOL TABLE:
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# CHECK-NEXT: 0000009f g F CODE my_func_export
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# CHECK-NEXT: 0000002a g O DATA my_global_export
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# CHECK-NEXT: 00000000 g TABLE my_table_export
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--- !WASM
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FileHeader:
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Version: 0x1
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Sections:
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- Type: TYPE
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Signatures:
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- Index: 0
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ParamTypes: []
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ReturnTypes: []
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- Type: IMPORT
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Imports:
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- Module: env
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Field: foo
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Kind: FUNCTION
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SigIndex: 0
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- Module: env
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Field: bar
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Kind: GLOBAL
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GlobalType: I32
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GlobalMutable: true
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- Module: env
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Field: memory
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Kind: MEMORY
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Memory:
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Minimum: 0x1
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- Type: FUNCTION
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FunctionTypes: [ 0 ]
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- Type: TABLE
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Tables:
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- Index: 0
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ElemType: FUNCREF
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Limits:
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Flags: [ HAS_MAX ]
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Minimum: 0x1
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Maximum: 0x1
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- Type: GLOBAL
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Globals:
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- Index: 1
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Mutable: false
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Type: I32
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InitExpr:
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Opcode: I32_CONST
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Value: 42
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- Type: EXPORT
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Exports:
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- Name: my_func_export
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Kind: FUNCTION
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Index: 1
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- Name: my_global_export
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Kind: GLOBAL
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Index: 1
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- Name: my_table_export
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Kind: TABLE
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Index: 0
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- Type: CODE
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Functions:
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- Index: 1
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Locals:
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Body: 00
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- Type: DATA
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Segments:
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- SectionOffset: 0
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InitFlags: 0
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Offset:
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Opcode: I32_CONST
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Value: 0
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Content: ''
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