[WebAssembly] Symbol changes #4c: import weak, LLD only

[ncw]

Summary

When D42105 was landed, a chunk from it was discarded.

This review re-commits that specific chunk, plus a test that exercises it.

Changes:

• When using --emit-relocs or --relocatable, we really do need to import undefined weak symbols, since relocations are generated against them.
• The relocatable.ll test has been updated with an import of a weak undefined symbol to illustrate the issue.

It's not possible to commit the test separately from the fix - without the fix, the test crashes!

test/wasm/relocatable.ll

 ; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %p/Inputs/hello.ll -o %t.hello.o
 ; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %s -o %t.o
 ; RUN: lld -flavor wasm -r -o %t.wasm %t.hello.o %t.o
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 ; Function Attrs: nounwind
 define hidden i32 @my_func() local_unnamed_addr {
 entry:
   %call = tail call i32 @foo_import()
+  %call2 = tail call i32 @bar_import()
   ret i32 1
 }
 
 declare i32 @foo_import() local_unnamed_addr
+declare extern_weak i32 @bar_import() local_unnamed_addr
 @data_import = external global i64
 
 @func_addr1 = hidden global i32()* @my_func, align 4
 @func_addr2 = hidden global i32()* @foo_import, align 4
+@func_addr3 = hidden global i32()* @bar_import, align 4
 @data_addr1 = hidden global i64* @data_import, align 8
 
 $func_comdat = comdat any
 @data_comdat = weak_odr constant [3 x i8] c"abc", comdat($func_comdat)
 define linkonce_odr i32 @func_comdat() comdat {
 entry:
   ret i32 ptrtoint ([3 x i8]* @data_comdat to i32)
 }

 ; CHECK-NEXT:         Field:           puts
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         SigIndex:        1
 ; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           foo_import
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         SigIndex:        2
 ; CHECK-NEXT:       - Module:          env
+; CHECK-NEXT:         Field:           bar_import
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         SigIndex:        2
+; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           data_import
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         GlobalType:      I32
 ; CHECK-NEXT:         GlobalMutable:   false
 ; CHECK-NEXT:   - Type:            FUNCTION
 ; CHECK-NEXT:     FunctionTypes:   [ 0, 2, 2 ]
 ; CHECK-NEXT:   - Type:            TABLE
 ; CHECK-NEXT:     Tables:
 ; CHECK-NEXT:       - ElemType:        ANYFUNC
 ; CHECK-NEXT:         Limits:
 ; CHECK-NEXT:           Flags:           [ HAS_MAX ]
-; CHECK-NEXT:           Initial:         0x00000002
-; CHECK-NEXT:           Maximum:         0x00000002
+; CHECK-NEXT:           Initial:         0x00000003
+; CHECK-NEXT:           Maximum:         0x00000003
 ; CHECK-NEXT:   - Type:            MEMORY
 ; CHECK-NEXT:     Memories:
 ; CHECK-NEXT:       - Initial:         0x00000001
 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           0
 ; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           20
+; CHECK-NEXT:           Value:           28
 ; CHECK-NEXT:       - Index:           3
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           8
 ; CHECK-NEXT:       - Index:           4
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           12
 ; CHECK-NEXT:       - Index:           5
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           16
+; CHECK-NEXT:       - Index:           6
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         false
+; CHECK-NEXT:         InitExpr:
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           24
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            hello
 ; CHECK-NEXT:         Kind:            FUNCTION
-; CHECK-NEXT:         Index:           2
+; CHECK-NEXT:         Index:           3
 ; CHECK-NEXT:       - Name:            my_func
 ; CHECK-NEXT:         Kind:            FUNCTION
-; CHECK-NEXT:         Index:           3
+; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:       - Name:            func_comdat
 ; CHECK-NEXT:         Kind:            FUNCTION
-; CHECK-NEXT:         Index:           4
+; CHECK-NEXT:         Index:           5
 ; CHECK-NEXT:       - Name:            hello_str
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:       - Name:            data_comdat
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            func_addr1
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           3
 ; CHECK-NEXT:       - Name:            func_addr2
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           4
-; CHECK-NEXT:       - Name:            data_addr1
+; CHECK-NEXT:       - Name:            func_addr3
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           5
+; CHECK-NEXT:       - Name:            data_addr1
+; CHECK-NEXT:         Kind:            GLOBAL
+; CHECK-NEXT:         Index:           6
 ; CHECK-NEXT:   - Type:            ELEM
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           0
-; CHECK-NEXT:         Functions:       [ 3, 1 ]
+; CHECK-NEXT:         Functions:       [ 4, 1, 2 ]
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Relocations:
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:         Offset:          0x00000004
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_FUNCTION_INDEX_LEB
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:         Offset:          0x0000000A
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_FUNCTION_INDEX_LEB
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:         Offset:          0x00000013
+; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_FUNCTION_INDEX_LEB
+; CHECK-NEXT:         Index:           2
+; CHECK-NEXT:         Offset:          0x0000001A
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
 ; CHECK-NEXT:         Index:           2
-; CHECK-NEXT:         Offset:          0x0000001F
+; CHECK-NEXT:         Offset:          0x00000026
 ; CHECK-NEXT:     Functions:
-; CHECK-NEXT:       - Index:         2
-; CHECK-NEXT:         Locals:
-; CHECK-NEXT:         Body:          4180808080001080808080000B
 ; CHECK-NEXT:       - Index:         3
 ; CHECK-NEXT:         Locals:
-; CHECK-NEXT:         Body:          1081808080001A41010B
-; CHECK-NEXT:       - Index:           4
+; CHECK-NEXT:         Body:          4180808080001080808080000B
+; CHECK-NEXT:       - Index:         4
 ; CHECK-NEXT:         Locals:
-; CHECK-NEXT:         Body:            4194808080000B
+; CHECK-NEXT:         Body:          1081808080001A1082808080001A41010B
+; CHECK-NEXT:       - Index:         5
+; CHECK-NEXT:         Locals:
+; CHECK-NEXT:         Body:          419C808080000B
 ; CHECK-NEXT:   - Type:            DATA
 ; CHECK-NEXT:     Relocations:
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_I32
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:         Offset:          0x00000012
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_I32
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:         Offset:          0x0000001B
+; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_I32
+; CHECK-NEXT:         Index:           2
+; CHECK-NEXT:         Offset:          0x00000024
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_I32
 ; CHECK-NEXT:         Index:           0
-; CHECK-NEXT:         Offset:          0x00000024
+; CHECK-NEXT:         Offset:          0x0000002D
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - SectionOffset:   6
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           0
 ; CHECK-NEXT:         Content:         68656C6C6F0A00
 ; CHECK-NEXT:       - SectionOffset:   18
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           8
 ; CHECK-NEXT:         Content:         '00000000'
 ; CHECK-NEXT:       - SectionOffset:   27
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           12
 ; CHECK-NEXT:         Content:         '01000000'
 ; CHECK-NEXT:       - SectionOffset:   36
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           16
-; CHECK-NEXT:         Content:         '00000000'
+; CHECK-NEXT:         Content:         '02000000'
 ; CHECK-NEXT:       - SectionOffset:   45
 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           20
+; CHECK-NEXT:           Value:           24
+; CHECK-NEXT:         Content:         '00000000'
+; CHECK-NEXT:       - SectionOffset:   54
+; CHECK-NEXT:         MemoryIndex:     0
+; CHECK-NEXT:         Offset:
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           28
 ; CHECK-NEXT:         Content:         '616263'
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            linking
-; CHECK-NEXT:     DataSize:        23
+; CHECK-NEXT:     DataSize:        31
 ; CHECK-NEXT:     SymbolInfo:
 ; CHECK-NEXT:       - Name:            hello
 ; CHECK-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
 ; CHECK-NEXT:       - Name:            my_func
 ; CHECK-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
 ; CHECK-NEXT:       - Name:            func_comdat
 ; CHECK-NEXT:         Flags:           [ BINDING_WEAK ]
 ; CHECK-NEXT:       - Name:            data_comdat
 ; CHECK-NEXT:         Flags:           [ BINDING_WEAK ]
 ; CHECK-NEXT:       - Name:            func_addr1
 ; CHECK-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
 ; CHECK-NEXT:       - Name:            func_addr2
 ; CHECK-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; CHECK-NEXT:       - Name:            func_addr3
+; CHECK-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
 ; CHECK-NEXT:       - Name:            data_addr1
 ; CHECK-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
 ; CHECK-NEXT:     SegmentInfo:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Name:            .rodata.hello_str
 ; CHECK-NEXT:         Alignment:       1
 ; CHECK-NEXT:         Flags:           [  ]
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Name:            .data.func_addr1
 ; CHECK-NEXT:         Alignment:       4
 ; CHECK-NEXT:         Flags:           [  ]
 ; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Name:            .data.func_addr2
 ; CHECK-NEXT:         Alignment:       4
 ; CHECK-NEXT:         Flags:           [  ]
 ; CHECK-NEXT:       - Index:           3
+; CHECK-NEXT:         Name:            .data.func_addr3
+; CHECK-NEXT:         Alignment:       4
+; CHECK-NEXT:         Flags:           [  ]
+; CHECK-NEXT:       - Index:           4
 ; CHECK-NEXT:         Name:            .data.data_addr1
 ; CHECK-NEXT:         Alignment:       8
 ; CHECK-NEXT:         Flags:           [  ]
-; CHECK-NEXT:       - Index:           4
+; CHECK-NEXT:       - Index:           5
 ; CHECK-NEXT:         Name:            .rodata.data_comdat
 ; CHECK-NEXT:         Alignment:       1
 ; CHECK-NEXT:         Flags:           [  ]
 ; CHECK-NEXT:     Comdats:
 ; CHECK-NEXT:       - Name:            func_comdat
 ; CHECK-NEXT:         Entries:
 ; CHECK-NEXT:           - Kind:            FUNCTION
-; CHECK-NEXT:             Index:           4
+; CHECK-NEXT:             Index:           5
 ; CHECK-NEXT:           - Kind:            DATA
-; CHECK-NEXT:             Index:           4
+; CHECK-NEXT:             Index:           5
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            name
 ; CHECK-NEXT:     FunctionNames:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Name:            puts
 ; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         Name:            foo_import
 ; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         Name:            hello
+; CHECK-NEXT:         Name:            bar_import
 ; CHECK-NEXT:       - Index:           3
-; CHECK-NEXT:         Name:            my_func
+; CHECK-NEXT:         Name:            hello
 ; CHECK-NEXT:       - Index:           4
+; CHECK-NEXT:         Name:            my_func
+; CHECK-NEXT:       - Index:           5
 ; CHECK-NEXT:         Name:            func_comdat
 ; CHECK-NEXT: ...

wasm/Writer.cpp

for (OutputSection *S : OutputSections) {
     S->setOffset(FileSize);
     S->finalizeContents();
     FileSize += S->getSize();
   }
 }
 
 void Writer::calculateImports() {
   for (Symbol *Sym : Symtab->getSymbols()) {
-    if (!Sym->isUndefined() || Sym->isWeak())
+    if (!Sym->isUndefined() || (Sym->isWeak() && !Config->EmitRelocs))
       continue;
 
     if (Sym->isFunction()) {
       Sym->setOutputIndex(ImportedFunctions.size());
       ImportedFunctions.push_back(Sym);
     } else {
       Sym->setOutputIndex(ImportedGlobals.size());
       ImportedGlobals.push_back(Sym);