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Merged
merged 10 commits into from
Jun 21, 2024
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[lld][WebAssembly] Return 0 for synthetic function offsets #96134

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d5ba71e
[lld][WebAssembly] Return 0 for synthetic function offsets
aheejin Jun 20, 2024
f463f91
Remove `entry`
aheejin Jun 20, 2024
88a48b2
Add 'weak' linkage to duplicate functions
aheejin Jun 20, 2024
ea4eb9a
Remove DILocations
aheejin Jun 20, 2024
6f7d8cd
Add s files
aheejin Jun 20, 2024
607b92a
Simplify .s files a little
aheejin Jun 20, 2024
165246a
Simplify .s files very much
aheejin Jun 20, 2024
dc1ad4c
Remove .ll files
aheejin Jun 20, 2024
9cd6790
Test comment fix
aheejin Jun 20, 2024
98d9243
Add newline in test
aheejin Jun 20, 2024
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31 changes: 31 additions & 0 deletions lld/test/wasm/Inputs/signature-mismatch-debug-info-a.ll
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@@ -0,0 +1,31 @@
target triple = "wasm32-unknown-emscripten"

define void @foo(i32 %a) !dbg !6 {
ret void
}

define void @test0() !dbg !10 {
entry:
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Why does this function have entry: but not the one above?

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I generated these tests from .c file and manually removed some unnecessary parts, and I think I left some entrys. Removed them for consistency.

call void @foo(i32 3), !dbg !13
ret void, !dbg !14
}

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!2, !3, !4}
!llvm.ident = !{!5}

!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 19.0.0git", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "a.c", directory: "")
!2 = !{i32 7, !"Dwarf Version", i32 4}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!4 = !{i32 1, !"wchar_size", i32 4}
!5 = !{!"clang version 19.0.0git"}
!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !7, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
!7 = !DISubroutineType(types: !8)
!8 = !{null, !9}
!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!10 = distinct !DISubprogram(name: "test0", scope: !1, file: !1, line: 7, type: !11, scopeLine: 7, spFlags: DISPFlagDefinition, unit: !0)
!11 = !DISubroutineType(types: !12)
!12 = !{null}
!13 = !DILocation(line: 8, column: 3, scope: !10)
!14 = !DILocation(line: 9, column: 1, scope: !10)
31 changes: 31 additions & 0 deletions lld/test/wasm/Inputs/signature-mismatch-debug-info-b.ll
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target triple = "wasm32-unknown-emscripten"

define void @foo(i32 %a, i32 %b) !dbg !6 {
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Why does this not result in a link error due to multiple definitions of foo?

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I don't know. They are not marked as weak, so it's weird... I tested with system (x86) clang and gcc and they all seem to error out.

When we do this by LTO, meaning running wasm-ld directly on bitcode, they error out saying duplicate definition. When does this "signature mismatch" occur usually? When a definition and a callsite do not match in the signature?

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IIUC, regardless of signature... you can't have two global definitions of foo in the same program unless one of them is weak. So I can't see why this wouldn't fail, even with matching signatures.

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Not sure why the current non-weak functions don't error out, but changed the test function linkages to be weak, which should not error out.

ret void
}

define void @test1() !dbg !10 {
entry:
call void @foo(i32 4, i32 5), !dbg !13
ret void, !dbg !14
}

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!2, !3, !4}
!llvm.ident = !{!5}

!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 19.0.0git", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "b.c", directory: "")
!2 = !{i32 7, !"Dwarf Version", i32 4}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!4 = !{i32 1, !"wchar_size", i32 4}
!5 = !{!"clang version 19.0.0git"}
!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !7, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
!7 = !DISubroutineType(types: !8)
!8 = !{null, !9, !9}
!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!10 = distinct !DISubprogram(name: "test1", scope: !1, file: !1, line: 7, type: !11, scopeLine: 7, spFlags: DISPFlagDefinition, unit: !0)
!11 = !DISubroutineType(types: !12)
!12 = !{null}
!13 = !DILocation(line: 8, column: 3, scope: !10)
!14 = !DILocation(line: 9, column: 1, scope: !10)
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These tests include a lot of stuff that is perhaps not completely relevant to the bug I guess? Can we remove any of these lines that are not needed? Or is it better to keep them more like clang-generated bitcode?

One thing that would be great would be if we could write this in .s format... how does the .s format look for these tests? is it even more verbose?

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@aheejin aheejin Jun 20, 2024 •
edited
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This is what I got after I spent some time deleting unnecessary debug info already... I can further delete DILocation nodes and the line debug info attached to instructions. But we at least need DICompileUnit and DISubprogram and other nodes that are (transitively) referenced by those nodes.

Can I attach debug info in .s files? If so, can you point me to an example?

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I think simply converting these files to .s will include the debug info. I'm not sure it will be harder to easier to read.

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@aheejin aheejin Jun 20, 2024 •
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Converting these files to .s files generated this, which was too verbose: 6f7d8cd

So I just rewrote them just enough to reproduce the error: 165246a
(Turns out just mentioning the function name in .debug_info section was sufficient to reproduce the error)

30 changes: 30 additions & 0 deletions lld/test/wasm/Inputs/signature-mismatch-debug-info-main.ll
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@@ -0,0 +1,30 @@
target triple = "wasm32-unknown-emscripten"

define i32 @main() !dbg !6 {
entry:
call void @test0(), !dbg !10
call void @test1(), !dbg !11
ret i32 0, !dbg !12
}

declare void @test0()

declare void @test1()

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!2, !3, !4}
!llvm.ident = !{!5}

!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 19.0.0git", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "main.c", directory: "")
!2 = !{i32 7, !"Dwarf Version", i32 4}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!4 = !{i32 1, !"wchar_size", i32 4}
!5 = !{!"clang version 19.0.0git"}
!6 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 4, type: !7, scopeLine: 4, spFlags: DISPFlagDefinition, unit: !0)
!7 = !DISubroutineType(types: !8)
!8 = !{!9}
!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!10 = !DILocation(line: 5, column: 3, scope: !6)
!11 = !DILocation(line: 6, column: 3, scope: !6)
!12 = !DILocation(line: 7, column: 3, scope: !6)
8 changes: 8 additions & 0 deletions lld/test/wasm/signature-mismatch-debug-info.test
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# This is a regression test that checks whether a function signature mismatch
# in functions with debug info does not cause does not cause a segmentation
# fault when writing .debug_info section.

; RUN: llc -filetype=obj %p/Inputs/signature-mismatch-debug-info-a.ll -o %t.a.o
; RUN: llc -filetype=obj %p/Inputs/signature-mismatch-debug-info-b.ll -o %t.b.o
; RUN: llc -filetype=obj %p/Inputs/signature-mismatch-debug-info-main.ll -o %t.main.o
; RUN: wasm-ld -o %t.wasm %t.a.o %t.b.o %t.main.o --export=main --no-entry
11 changes: 9 additions & 2 deletions lld/wasm/InputChunks.h
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Expand Up @@ -279,7 +279,14 @@ class InputFunction : public InputChunk {
}
void setExportName(std::string exportName) { this->exportName = exportName; }
uint32_t getFunctionInputOffset() const { return getInputSectionOffset(); }
uint32_t getFunctionCodeOffset() const { return function->CodeOffset; }
uint32_t getFunctionCodeOffset() const {
// For generated synthetic functions, such as unreachable stubs generated
// for signature mismatches, 'function' reference does not exist. This
// function is used to get function offsets for .debug_info section, and for
// those generated stubs function offsets are not meaningful anyway. So just
// return 0 in those cases.
return function ? function->CodeOffset : 0;
}
uint32_t getFunctionIndex() const { return *functionIndex; }
bool hasFunctionIndex() const { return functionIndex.has_value(); }
void setFunctionIndex(uint32_t index);
Expand All @@ -301,7 +308,7 @@ class InputFunction : public InputChunk {
return compressedSize;
}

const WasmFunction *function;
const WasmFunction *function = nullptr;

protected:
std::optional<std::string> exportName;
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