[WebAssembly] Symbol changes #4: export relocatable, LLD only

[ncw]

Summary

Fourth chunk split out of D41955.

There is no corresponding LLVM patch to go along with this.

Headline: Fix some bugs in the existing handling of exports when LLD generates "relocatable" output

---

Changes:

• LLD's relocatable output was writing out an export for all globals (including file-local syms), but not for functions. Oops. To be consistent with non-relocatable output, all symbols (file-local and public) should be exported. Any symbol targetted by further relocations needs to be exported. The lack of local function exports was just an omission, I think.
• Second bug: Local symbol names can collide, causing an illegal Wasm file to be generated! Oops again. This only previously affected producing relocatable output from two files, where each had a global with the same name. We need to "budge" the symbol names for locals that are exported on relocatable output.
• Third bug: LLD's relocatable output wasn't writing out any symbol flags! Thus the local globals weren't being marked as local, and the hidden flag was also stripped...
• Added tests to exercise colliding local names with/without relocatable flag

[ncw]

Updated: Fix mistake not exporting weak flag

test/wasm/call-indirect.ll

96

Test expectations updated: some benign reordering of the imports, due to iterating over Symbols in order of definition, rather than in order of first use

test/wasm/init-fini.ll

146

Test expectation updated: HIDDEN/LOCAL flag should be written out for LLD's relocatable output

[ncw]

Updated: tiny tweak to calculateImports to fix up case of unresolved weak globals

[ncw]

wasm/Writer.cpp

617

I realise that std::set<std::string> isn't very idiomatic in LLVM, but you can why I chose it. I couldn't think of another way of doing it though that didn't require more code doing explicit buffer management.

Suggestions welcome - otherwise it's hopefully "good enough" for now, especially as it's short-lived and only used for exported functions (which I'd expect to be a small number compared to the overall output size).

[ncw]

Updated:

• Fixed test after rebase on top of __heap_base change

[sbc100]

Just a couple of minor nits

test/wasm/Inputs/locals-duplicate1.ll

2

Are there llvm terms you can use here rather than local and public? I think llvm this internal and external linkage, right?

test/wasm/locals-duplicate.test

2

Can we give these new files better names? Perhaps duplicate-symbols-internal.test. Locals makes me think of wasm locals, and llvm doesn't use the term local for these symbols either (I think?).

wasm/Writer.cpp

617

I think llvm::DenseSet<StringRef> is used elsewhere in lld and probably makes sense here. Or llvm::StringSet? I'm not sure what the tradeoffs are between those two.

[ncw]

test/wasm/Inputs/locals-duplicate1.ll

2

Yes, you're right, maybe those are better terms. "XXX_LOCAL" is the name of the flag in the MC source code corresponding to the IR keyword "internal". "public" is because I couldn't think of the correct opposite!

test/wasm/locals-duplicate.test

2

Well in LLD we have Symbol::isLocal. The name you suggested is better though.

wasm/Writer.cpp

617

DenseSet<StringRef> and StringSet both assume that the string itself is owned externally. But the "budged" names can't be stored just as a StringRef, something needs to actually own the buffer to the string itself, hence using std::string. And you can't use a StringRef to refer to things in a vector<std::string> either (can you?) because you have to careful mutating the vector not to reallocate the strings and invalidate any StringRefs (I suppose we can rely on move ctors these days).

Nuisance. I don't suppose it's good style to use make<std::string> or similar magic to allocate strings?

I could maybe see about doing some more explicit buffer management to allow use of an llvm::StringSet.

[sbc100]

test/wasm/locals-duplicate.test

2

Hmm, you are right. Confusing different nomenclature. I think its because in ELF and Wasm binary format we use local and global. Given that I'm OK with the local and global here.. but maybe just replace public with global?

wasm/Writer.cpp

617

In that case std::set seems reasonable to me.

[ncw]

Updated:

• Fixed terminology in comments
• Use llvm::StringSaver to get rid of std::set<std::string> in favour of llvm::StringSet

wasm/Writer.cpp

617

Aha! With some more searching, I've found the idiomatic LLVM solution.

It's called llvm::Saver, a global instance of llvm::StringSaver that lets you get a safe/stable StringRef for a fresh string.

Updated now to use that.

[sbc100]

wasm/Writer.cpp

617

Nice!

I'm not familiar with StringSaver, but would it make sense to use a saver that has the same lifetime as UsedNames? i.e. a function scoped saver?

[sbc100]

wasm/Writer.cpp

600

I think this is unrelated? At least all the tests still pass without this line.

[sbc100]

wasm/Writer.cpp

390

Don't we want to iterate through all symbols here, not just the exported ones? This can be a followup change I think.

[inglorion]

lld/trunk/wasm/Writer.cpp

67 ↗

(On Diff #130504)

gcc seems unhappy with this declaration. It complains:

llvm/tools/lld/wasm/Writer.cpp:67:17: error: declaration of ‘const lld::wasm::Symbol* {anonymous}::WasmExportEntry::Symbol’ [-fpermissive]
   const Symbol *Symbol;
             ^
In file included from llvm/tools/lld/wasm/Config.h:17:0,
                 from llvm/tools/lld/wasm/Writer.cpp:13:
llvm/tools/lld/wasm/Symbols.h:27:7: error: changes meaning of ‘Symbol’ from ‘class lld::wasm::Symbol’ [-fpermissive]
 class Symbol {
       ^

I have put up D42278 to rename the field and stop the naming collision.

[sbc100]

lld/trunk/wasm/Writer.cpp

67 ↗

(On Diff #130504)

Thanks! I already had a local version ready to go so I'll just push that if thats OK?

[ncw]

wasm/Writer.cpp

390

Oh! For "defined" symbols, we can't iterate through the non-exported ones (any functions not exported don't correspond to a Symbol).

But yes, the imports need to be included too. Oops.

600

It is needed eventually; Patch #5 will fail without it. This is similar to patch #4b (D42237). Maybe I split this badly and it should have gone in with that...

I'll pull this out into another patch.

617

A function-scoped one wouldn't work. The StringSet<> UsedNames is function-local, but the StringRefs that are returned get put into the WasmExportEntrys in ExportedSymbols, so are used outside this function.

test/wasm/Inputs/locals-duplicate1.ll

+; Will collide: local (internal linkage) with global (external) linkage
+@colliding_global1 = internal default global i32 0, align 4
+; Will collide: global with local
+@colliding_global2 = default global i32 0, align 4
+; Will collide: local with local
+@colliding_global3 = internal default global i32 0, align 4
+
+; Will collide: local with global
+define internal i32 @colliding_func1() {
+entry:
+  ret i32 2
+}
+; Will collide: global with local
+define i32 @colliding_func2() {
+entry:
+  ret i32 2
+}
+; Will collide: local with local
+define internal i32 @colliding_func3() {
+entry:
+  ret i32 2
+}
+
+
+define i32* @get_global1A() {
+entry:
+  ret i32* @colliding_global1
+}
+define i32* @get_global2A() {
+entry:
+  ret i32* @colliding_global2
+}
+define i32* @get_global3A() {
+entry:
+  ret i32* @colliding_global3
+}
+
+define i32 ()* @get_func1A() {
+entry:
+  ret i32 ()* @colliding_func1
+}
+define i32 ()* @get_func2A() {
+entry:
+  ret i32 ()* @colliding_func2
+}
+define i32 ()* @get_func3A() {
+entry:
+  ret i32 ()* @colliding_func3
+}

test/wasm/Inputs/locals-duplicate2.ll

+; Will collide: local (internal linkage) with global (external) linkage
+@colliding_global1 = default global i32 0, align 4
+; Will collide: global with local
+@colliding_global2 = internal default global i32 0, align 4
+; Will collide: local with local
+@colliding_global3 = internal default global i32 0, align 4
+
+; Will collide: local with global
+define i32 @colliding_func1() {
+entry:
+  ret i32 2
+}
+; Will collide: global with local
+define internal i32 @colliding_func2() {
+entry:
+  ret i32 2
+}
+; Will collide: local with local
+define internal i32 @colliding_func3() {
+entry:
+  ret i32 2
+}
+
+
+define i32* @get_global1B() {
+entry:
+  ret i32* @colliding_global1
+}
+define i32* @get_global2B() {
+entry:
+  ret i32* @colliding_global2
+}
+define i32* @get_global3B() {
+entry:
+  ret i32* @colliding_global3
+}
+
+define i32 ()* @get_func1B() {
+entry:
+  ret i32 ()* @colliding_func1
+}
+define i32 ()* @get_func2B() {
+entry:
+  ret i32 ()* @colliding_func2
+}
+define i32 ()* @get_func3B() {
+entry:
+  ret i32 ()* @colliding_func3
+}

test/wasm/call-indirect.ll

 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           3
-; CHECK-NEXT:       - Name:            foo
-; CHECK-NEXT:         Kind:            FUNCTION
-; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            bar
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            call_bar_indirect
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
+; CHECK-NEXT:       - Name:            foo
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           2
 ; CHECK-NEXT:       - Name:            call_ptr
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:       - Name:            __heap_base
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:   - Type:            ELEM
 ; CHECK-NEXT:     Segments:

test/wasm/init-fini.ll

 ; CHECK-NEXT: ...
 
 
 ; RUN: lld -flavor wasm -r %t.o %t.global-ctor-dtor.o -o %t.reloc.wasm
 ; RUN: obj2yaml %t.reloc.wasm | FileCheck -check-prefix=RELOC %s
 
 ; RELOC:          Name:            linking
 ; RELOC-NEXT:     DataSize:        0
-; RELOC-NEXT:     InitFunctions:   
+; RELOC-NEXT:     SymbolInfo:      
+; RELOC-NEXT:       - Name:            func1
+; RELOC-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; RELOC-NEXT:       - Name:            func2
+; RELOC-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; RELOC-NEXT:       - Name:            func3
+; RELOC-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; RELOC-NEXT:       - Name:            func4
+; RELOC-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; RELOC-NEXT:       - Name:            _start
+; RELOC-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; RELOC-NEXT:       - Name:            .Lcall_dtors.101
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lregister_call_dtors.101
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lbitcast
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lcall_dtors.1001
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lregister_call_dtors.1001
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            myctor
+; RELOC-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; RELOC-NEXT:       - Name:            mydtor
+; RELOC-NEXT:         Flags:           [ VISIBILITY_HIDDEN ]
+; RELOC-NEXT:       - Name:            .Lcall_dtors.101.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lregister_call_dtors.101.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lcall_dtors.202
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lregister_call_dtors.202
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lcall_dtors.2002
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            .Lregister_call_dtors.2002
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:     InitFunctions:
 ; RELOC-NEXT:       - Priority:        101
 ; RELOC-NEXT:         FunctionIndex:   0
 ; RELOC-NEXT:       - Priority:        101
 ; RELOC-NEXT:         FunctionIndex:   1
 ; RELOC-NEXT:       - Priority:        101
 ; RELOC-NEXT:         FunctionIndex:   7
 ; RELOC-NEXT:       - Priority:        101
 ; RELOC-NEXT:         FunctionIndex:   11

test/wasm/locals-duplicate.test

+; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %p/Inputs/locals-duplicate1.ll -o %t1.o
+; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %p/Inputs/locals-duplicate2.ll -o %t2.o
+; RUN: lld -flavor wasm --no-entry -o %t.wasm %t1.o %t2.o
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; CHECK:      --- !WASM
+; CHECK-NEXT: FileHeader:      
+; CHECK-NEXT:   Version:         0x00000001
+; CHECK-NEXT: Sections:        
+; CHECK-NEXT:   - Type:            TYPE
+; CHECK-NEXT:     Signatures:      
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         ReturnType:      I32
+; CHECK-NEXT:         ParamTypes:      
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         ReturnType:      NORESULT
+; CHECK-NEXT:         ParamTypes:      
+; CHECK-NEXT:   - Type:            FUNCTION
+; CHECK-NEXT:     FunctionTypes:   [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+; CHECK-NEXT:                        0, 0, 1 ]
+; CHECK-NEXT:   - Type:            TABLE
+; CHECK-NEXT:     Tables:          
+; CHECK-NEXT:       - ElemType:        ANYFUNC
+; CHECK-NEXT:         Limits:          
+; CHECK-NEXT:           Flags:           [ HAS_MAX ]
+; CHECK-NEXT:           Initial:         0x00000007
+; CHECK-NEXT:           Maximum:         0x00000007
+; CHECK-NEXT:   - Type:            MEMORY
+; CHECK-NEXT:     Memories:        
+; CHECK-NEXT:       - Initial:         0x00000002
+; CHECK-NEXT:   - Type:            GLOBAL
+; CHECK-NEXT:     Globals:         
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         true
+; CHECK-NEXT:         InitExpr:        
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           66592
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         false
+; CHECK-NEXT:         InitExpr:
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           66592
+; CHECK-NEXT:   - Type:            EXPORT
+; CHECK-NEXT:     Exports:         
+; CHECK-NEXT:       - Name:            memory
+; CHECK-NEXT:         Kind:            MEMORY
+; CHECK-NEXT:         Index:           0
+; CHECK-NEXT:       - Name:            colliding_func2
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           1
+; CHECK-NEXT:       - Name:            get_global1A
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           3
+; CHECK-NEXT:       - Name:            get_global2A
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           4
+; CHECK-NEXT:       - Name:            get_global3A
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           5
+; CHECK-NEXT:       - Name:            get_func1A
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           6
+; CHECK-NEXT:       - Name:            get_func2A
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           7
+; CHECK-NEXT:       - Name:            get_func3A
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           8
+; CHECK-NEXT:       - Name:            colliding_func1
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           9
+; CHECK-NEXT:       - Name:            get_global1B
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           12
+; CHECK-NEXT:       - Name:            get_global2B
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           13
+; CHECK-NEXT:       - Name:            get_global3B
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           14
+; CHECK-NEXT:       - Name:            get_func1B
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           15
+; CHECK-NEXT:       - Name:            get_func2B
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           16
+; CHECK-NEXT:       - Name:            get_func3B
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           17
+; CHECK-NEXT:       - Name:            __heap_base
+; CHECK-NEXT:         Kind:            GLOBAL
+; CHECK-NEXT:         Index:           1
+; CHECK-NEXT:   - Type:            ELEM
+; CHECK-NEXT:     Segments:        
+; CHECK-NEXT:       - Offset:          
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           1
+; CHECK-NEXT:         Functions:       [ 0, 1, 2, 9, 10, 11 ]
+; CHECK-NEXT:   - Type:            CODE
+; CHECK-NEXT:     Functions:       
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            41020B
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            41020B
+; CHECK-NEXT:       - Index:           2
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            41020B
+; CHECK-NEXT:       - Index:           3
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4180888080000B
+; CHECK-NEXT:       - Index:           4
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4184888080000B
+; CHECK-NEXT:       - Index:           5
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4188888080000B
+; CHECK-NEXT:       - Index:           6
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4181808080000B
+; CHECK-NEXT:       - Index:           7
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4182808080000B
+; CHECK-NEXT:       - Index:           8
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4183808080000B
+; CHECK-NEXT:       - Index:           9
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            41020B
+; CHECK-NEXT:       - Index:           10
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            41020B
+; CHECK-NEXT:       - Index:           11
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            41020B
+; CHECK-NEXT:       - Index:           12
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            418C888080000B
+; CHECK-NEXT:       - Index:           13
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4190888080000B
+; CHECK-NEXT:       - Index:           14
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4194888080000B
+; CHECK-NEXT:       - Index:           15
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4184808080000B
+; CHECK-NEXT:       - Index:           16
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4185808080000B
+; CHECK-NEXT:       - Index:           17
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            4186808080000B
+; CHECK-NEXT:       - Index:           18
+; CHECK-NEXT:         Locals:          
+; CHECK-NEXT:         Body:            0B
+; CHECK-NEXT:   - Type:            DATA
+; CHECK-NEXT:     Segments:        
+; CHECK-NEXT:       - SectionOffset:   7
+; CHECK-NEXT:         MemoryIndex:     0
+; CHECK-NEXT:         Offset:          
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           1024
+; CHECK-NEXT:         Content:         '000000000000000000000000000000000000000000000000'
+; CHECK-NEXT:   - Type:            CUSTOM
+; CHECK-NEXT:     Name:            linking
+; CHECK-NEXT:     DataSize:        24
+; CHECK-NEXT:   - Type:            CUSTOM
+; CHECK-NEXT:     Name:            name
+; CHECK-NEXT:     FunctionNames:   
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Name:            colliding_func1
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         Name:            colliding_func2
+; CHECK-NEXT:       - Index:           2
+; CHECK-NEXT:         Name:            colliding_func3
+; CHECK-NEXT:       - Index:           3
+; CHECK-NEXT:         Name:            get_global1A
+; CHECK-NEXT:       - Index:           4
+; CHECK-NEXT:         Name:            get_global2A
+; CHECK-NEXT:       - Index:           5
+; CHECK-NEXT:         Name:            get_global3A
+; CHECK-NEXT:       - Index:           6
+; CHECK-NEXT:         Name:            get_func1A
+; CHECK-NEXT:       - Index:           7
+; CHECK-NEXT:         Name:            get_func2A
+; CHECK-NEXT:       - Index:           8
+; CHECK-NEXT:         Name:            get_func3A
+; CHECK-NEXT:       - Index:           9
+; CHECK-NEXT:         Name:            colliding_func1
+; CHECK-NEXT:       - Index:           10
+; CHECK-NEXT:         Name:            colliding_func2
+; CHECK-NEXT:       - Index:           11
+; CHECK-NEXT:         Name:            colliding_func3
+; CHECK-NEXT:       - Index:           12
+; CHECK-NEXT:         Name:            get_global1B
+; CHECK-NEXT:       - Index:           13
+; CHECK-NEXT:         Name:            get_global2B
+; CHECK-NEXT:       - Index:           14
+; CHECK-NEXT:         Name:            get_global3B
+; CHECK-NEXT:       - Index:           15
+; CHECK-NEXT:         Name:            get_func1B
+; CHECK-NEXT:       - Index:           16
+; CHECK-NEXT:         Name:            get_func2B
+; CHECK-NEXT:       - Index:           17
+; CHECK-NEXT:         Name:            get_func3B
+; CHECK-NEXT:       - Index:           18
+; CHECK-NEXT:         Name:            __wasm_call_ctors
+; CHECK-NEXT: ...
+
+
+; RUN: lld -flavor wasm -r --no-entry -o %t.reloc.wasm %t1.o %t2.o
+; RUN: obj2yaml %t.reloc.wasm | FileCheck -check-prefix=RELOC %s
+
+; RELOC:      --- !WASM
+; RELOC-NEXT: FileHeader:      
+; RELOC-NEXT:   Version:         0x00000001
+; RELOC-NEXT: Sections:        
+; RELOC-NEXT:   - Type:            TYPE
+; RELOC-NEXT:     Signatures:      
+; RELOC-NEXT:       - Index:           0
+; RELOC-NEXT:         ReturnType:      I32
+; RELOC-NEXT:         ParamTypes:      
+; RELOC-NEXT:   - Type:            FUNCTION
+; RELOC-NEXT:     FunctionTypes:   [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+; RELOC-NEXT:                        0, 0 ]
+; RELOC-NEXT:   - Type:            TABLE
+; RELOC-NEXT:     Tables:          
+; RELOC-NEXT:       - ElemType:        ANYFUNC
+; RELOC-NEXT:         Limits:          
+; RELOC-NEXT:           Flags:           [ HAS_MAX ]
+; RELOC-NEXT:           Initial:         0x00000007
+; RELOC-NEXT:           Maximum:         0x00000007
+; RELOC-NEXT:   - Type:            MEMORY
+; RELOC-NEXT:     Memories:        
+; RELOC-NEXT:       - Initial:         0x00000001
+; RELOC-NEXT:   - Type:            GLOBAL
+; RELOC-NEXT:     Globals:         
+; RELOC-NEXT:       - Index:           0
+; RELOC-NEXT:         Type:            I32
+; RELOC-NEXT:         Mutable:         false
+; RELOC-NEXT:         InitExpr:        
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           0
+; RELOC-NEXT:       - Index:           1
+; RELOC-NEXT:         Type:            I32
+; RELOC-NEXT:         Mutable:         false
+; RELOC-NEXT:         InitExpr:        
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           8
+; RELOC-NEXT:       - Index:           2
+; RELOC-NEXT:         Type:            I32
+; RELOC-NEXT:         Mutable:         false
+; RELOC-NEXT:         InitExpr:        
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           16
+; RELOC-NEXT:       - Index:           3
+; RELOC-NEXT:         Type:            I32
+; RELOC-NEXT:         Mutable:         false
+; RELOC-NEXT:         InitExpr:        
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           4
+; RELOC-NEXT:       - Index:           4
+; RELOC-NEXT:         Type:            I32
+; RELOC-NEXT:         Mutable:         false
+; RELOC-NEXT:         InitExpr:        
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           12
+; RELOC-NEXT:       - Index:           5
+; RELOC-NEXT:         Type:            I32
+; RELOC-NEXT:         Mutable:         false
+; RELOC-NEXT:         InitExpr:        
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           20
+; RELOC-NEXT:   - Type:            EXPORT
+; RELOC-NEXT:     Exports:         
+; RELOC-NEXT:       - Name:            colliding_func1.1
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           0
+; RELOC-NEXT:       - Name:            colliding_func2
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           1
+; RELOC-NEXT:       - Name:            colliding_func3
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           2
+; RELOC-NEXT:       - Name:            get_global1A
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           3
+; RELOC-NEXT:       - Name:            get_global2A
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           4
+; RELOC-NEXT:       - Name:            get_global3A
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           5
+; RELOC-NEXT:       - Name:            get_func1A
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           6
+; RELOC-NEXT:       - Name:            get_func2A
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           7
+; RELOC-NEXT:       - Name:            get_func3A
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           8
+; RELOC-NEXT:       - Name:            colliding_func1
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           9
+; RELOC-NEXT:       - Name:            colliding_func2.1
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           10
+; RELOC-NEXT:       - Name:            colliding_func3.1
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           11
+; RELOC-NEXT:       - Name:            get_global1B
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           12
+; RELOC-NEXT:       - Name:            get_global2B
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           13
+; RELOC-NEXT:       - Name:            get_global3B
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           14
+; RELOC-NEXT:       - Name:            get_func1B
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           15
+; RELOC-NEXT:       - Name:            get_func2B
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           16
+; RELOC-NEXT:       - Name:            get_func3B
+; RELOC-NEXT:         Kind:            FUNCTION
+; RELOC-NEXT:         Index:           17
+; RELOC-NEXT:       - Name:            colliding_global1.1
+; RELOC-NEXT:         Kind:            GLOBAL
+; RELOC-NEXT:         Index:           0
+; RELOC-NEXT:       - Name:            colliding_global2
+; RELOC-NEXT:         Kind:            GLOBAL
+; RELOC-NEXT:         Index:           1
+; RELOC-NEXT:       - Name:            colliding_global3
+; RELOC-NEXT:         Kind:            GLOBAL
+; RELOC-NEXT:         Index:           2
+; RELOC-NEXT:       - Name:            colliding_global1
+; RELOC-NEXT:         Kind:            GLOBAL
+; RELOC-NEXT:         Index:           3
+; RELOC-NEXT:       - Name:            colliding_global2.1
+; RELOC-NEXT:         Kind:            GLOBAL
+; RELOC-NEXT:         Index:           4
+; RELOC-NEXT:       - Name:            colliding_global3.1
+; RELOC-NEXT:         Kind:            GLOBAL
+; RELOC-NEXT:         Index:           5
+; RELOC-NEXT:   - Type:            ELEM
+; RELOC-NEXT:     Segments:        
+; RELOC-NEXT:       - Offset:          
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           1
+; RELOC-NEXT:         Functions:       [ 0, 1, 2, 9, 10, 11 ]
+; RELOC-NEXT:   - Type:            CODE
+; RELOC-NEXT:     Relocations:     
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
+; RELOC-NEXT:         Index:           0
+; RELOC-NEXT:         Offset:          0x00000013
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
+; RELOC-NEXT:         Index:           1
+; RELOC-NEXT:         Offset:          0x0000001C
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
+; RELOC-NEXT:         Index:           2
+; RELOC-NEXT:         Offset:          0x00000025
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_SLEB
+; RELOC-NEXT:         Index:           0
+; RELOC-NEXT:         Offset:          0x0000002E
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_SLEB
+; RELOC-NEXT:         Index:           1
+; RELOC-NEXT:         Offset:          0x00000037
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_SLEB
+; RELOC-NEXT:         Index:           2
+; RELOC-NEXT:         Offset:          0x00000040
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
+; RELOC-NEXT:         Index:           3
+; RELOC-NEXT:         Offset:          0x00000058
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
+; RELOC-NEXT:         Index:           4
+; RELOC-NEXT:         Offset:          0x00000061
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_SLEB
+; RELOC-NEXT:         Index:           5
+; RELOC-NEXT:         Offset:          0x0000006A
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_SLEB
+; RELOC-NEXT:         Index:           9
+; RELOC-NEXT:         Offset:          0x00000073
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_SLEB
+; RELOC-NEXT:         Index:           10
+; RELOC-NEXT:         Offset:          0x0000007C
+; RELOC-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_SLEB
+; RELOC-NEXT:         Index:           11
+; RELOC-NEXT:         Offset:          0x00000085
+; RELOC-NEXT:     Functions:       
+; RELOC-NEXT:       - Index:           0
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            41020B
+; RELOC-NEXT:       - Index:           1
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            41020B
+; RELOC-NEXT:       - Index:           2
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            41020B
+; RELOC-NEXT:       - Index:           3
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4180808080000B
+; RELOC-NEXT:       - Index:           4
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4188808080000B
+; RELOC-NEXT:       - Index:           5
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4190808080000B
+; RELOC-NEXT:       - Index:           6
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4181808080000B
+; RELOC-NEXT:       - Index:           7
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4182808080000B
+; RELOC-NEXT:       - Index:           8
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4183808080000B
+; RELOC-NEXT:       - Index:           9
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            41020B
+; RELOC-NEXT:       - Index:           10
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            41020B
+; RELOC-NEXT:       - Index:           11
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            41020B
+; RELOC-NEXT:       - Index:           12
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4184808080000B
+; RELOC-NEXT:       - Index:           13
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            418C808080000B
+; RELOC-NEXT:       - Index:           14
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4194808080000B
+; RELOC-NEXT:       - Index:           15
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4184808080000B
+; RELOC-NEXT:       - Index:           16
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4185808080000B
+; RELOC-NEXT:       - Index:           17
+; RELOC-NEXT:         Locals:          
+; RELOC-NEXT:         Body:            4186808080000B
+; RELOC-NEXT:   - Type:            DATA
+; RELOC-NEXT:     Segments:        
+; RELOC-NEXT:       - SectionOffset:   6
+; RELOC-NEXT:         MemoryIndex:     0
+; RELOC-NEXT:         Offset:          
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           0
+; RELOC-NEXT:         Content:         '0000000000000000'
+; RELOC-NEXT:       - SectionOffset:   19
+; RELOC-NEXT:         MemoryIndex:     0
+; RELOC-NEXT:         Offset:          
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           8
+; RELOC-NEXT:         Content:         '0000000000000000'
+; RELOC-NEXT:       - SectionOffset:   32
+; RELOC-NEXT:         MemoryIndex:     0
+; RELOC-NEXT:         Offset:          
+; RELOC-NEXT:           Opcode:          I32_CONST
+; RELOC-NEXT:           Value:           16
+; RELOC-NEXT:         Content:         '0000000000000000'
+; RELOC-NEXT:   - Type:            CUSTOM
+; RELOC-NEXT:     Name:            linking
+; RELOC-NEXT:     DataSize:        24
+; RELOC-NEXT:     SymbolInfo:      
+; RELOC-NEXT:       - Name:            colliding_func1.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            colliding_func3
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            colliding_func2.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            colliding_func3.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            colliding_global1.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            colliding_global3
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            colliding_global2.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:       - Name:            colliding_global3.1
+; RELOC-NEXT:         Flags:           [ BINDING_LOCAL ]
+; RELOC-NEXT:     SegmentInfo:     
+; RELOC-NEXT:       - Index:           0
+; RELOC-NEXT:         Name:            .bss.colliding_global1
+; RELOC-NEXT:         Alignment:       4
+; RELOC-NEXT:         Flags:           [  ]
+; RELOC-NEXT:       - Index:           1
+; RELOC-NEXT:         Name:            .bss.colliding_global2
+; RELOC-NEXT:         Alignment:       4
+; RELOC-NEXT:         Flags:           [  ]
+; RELOC-NEXT:       - Index:           2
+; RELOC-NEXT:         Name:            .bss.colliding_global3
+; RELOC-NEXT:         Alignment:       4
+; RELOC-NEXT:         Flags:           [  ]
+; RELOC-NEXT:   - Type:            CUSTOM
+; RELOC-NEXT:     Name:            name
+; RELOC-NEXT:     FunctionNames:   
+; RELOC-NEXT:       - Index:           0
+; RELOC-NEXT:         Name:            colliding_func1
+; RELOC-NEXT:       - Index:           1
+; RELOC-NEXT:         Name:            colliding_func2
+; RELOC-NEXT:       - Index:           2
+; RELOC-NEXT:         Name:            colliding_func3
+; RELOC-NEXT:       - Index:           3
+; RELOC-NEXT:         Name:            get_global1A
+; RELOC-NEXT:       - Index:           4
+; RELOC-NEXT:         Name:            get_global2A
+; RELOC-NEXT:       - Index:           5
+; RELOC-NEXT:         Name:            get_global3A
+; RELOC-NEXT:       - Index:           6
+; RELOC-NEXT:         Name:            get_func1A
+; RELOC-NEXT:       - Index:           7
+; RELOC-NEXT:         Name:            get_func2A
+; RELOC-NEXT:       - Index:           8
+; RELOC-NEXT:         Name:            get_func3A
+; RELOC-NEXT:       - Index:           9
+; RELOC-NEXT:         Name:            colliding_func1
+; RELOC-NEXT:       - Index:           10
+; RELOC-NEXT:         Name:            colliding_func2
+; RELOC-NEXT:       - Index:           11
+; RELOC-NEXT:         Name:            colliding_func3
+; RELOC-NEXT:       - Index:           12
+; RELOC-NEXT:         Name:            get_global1B
+; RELOC-NEXT:       - Index:           13
+; RELOC-NEXT:         Name:            get_global2B
+; RELOC-NEXT:       - Index:           14
+; RELOC-NEXT:         Name:            get_global3B
+; RELOC-NEXT:       - Index:           15
+; RELOC-NEXT:         Name:            get_func1B
+; RELOC-NEXT:       - Index:           16
+; RELOC-NEXT:         Name:            get_func2B
+; RELOC-NEXT:       - Index:           17
+; RELOC-NEXT:         Name:            get_func3B
+; RELOC-NEXT: ...

test/wasm/relocatable.ll

 ; CHECK-NEXT:         MemoryIndex:     0
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           20
 ; CHECK-NEXT:         Content:         '616263'
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            linking
 ; CHECK-NEXT:     DataSize:        23
+; 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:            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

test/wasm/visibility-hidden.ll

 ; CHECK:        - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           2
-; CHECK-NEXT:       - Name:            archiveDefault
-; CHECK-NEXT:         Kind:            FUNCTION
-; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:       - Name:            objectDefault
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           1
+; CHECK-NEXT:       - Name:            archiveDefault
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           4
 ; CHECK-NEXT:       - Name:            __heap_base
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         Index:           1
 ; CHECK-NEXT:   - Type:

wasm/Writer.cpp

 #include "lld/Common/Threads.h"
 #include "llvm/Support/FileOutputBuffer.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/LEB128.h"
 
 #include <cstdarg>
 #include <map>
+#include <set>
 
 #define DEBUG_TYPE "lld"
 
 using namespace llvm;
 using namespace llvm::wasm;
 using namespace lld;
 using namespace lld::wasm;
 
for (int32_t Param : Sig.ParamTypes)
       Value += DenseMapInfo<int32_t>::getHashValue(Param);
     return Value;
   }
   static bool isEqual(const WasmSignature &LHS, const WasmSignature &RHS) {
     return LHS == RHS;
   }
 };
 
+// A Wasm export to be written into the export section.
+struct WasmExportEntry {
+  const Symbol *Symbol;
+  StringRef FieldName; // may not match the Symbol name
+};
+
 // The writer writes a SymbolTable result to a file.
 class Writer {
 public:
   void run();
 
 private:
   void openFile();
 
   uint32_t lookupType(const WasmSignature &Sig);
   uint32_t registerType(const WasmSignature &Sig);
   void createCtorFunction();
   void calculateInitFunctions();
   void assignIndexes();
   void calculateImports();
+  void calculateExports();
   void calculateTypes();
   void createOutputSegments();
   void layoutMemory();
   void createHeader();
   void createSections();
   SyntheticSection *createSyntheticSection(uint32_t Type,
                                            StringRef Name = "");
 
private:
   uint64_t FileSize = 0;
   uint32_t DataSize = 0;
   uint32_t NumMemoryPages = 0;
 
   std::vector<const WasmSignature *> Types;
   DenseMap<WasmSignature, int32_t, WasmSignatureDenseMapInfo> TypeIndices;
   std::vector<const Symbol *> ImportedFunctions;
   std::vector<const Symbol *> ImportedGlobals;
+  std::vector<WasmExportEntry> ExportedSymbols;
   std::vector<const Symbol *> DefinedGlobals;
   std::vector<InputFunction *> DefinedFunctions;
   std::vector<const Symbol *> IndirectFunctions;
   std::vector<WasmInitFunc> InitFunctions;
 
   // Elements that are used to construct the final output
   std::string Header;
   std::vector<OutputSection *> OutputSections;
void Writer::createTableSection() {
   writeSleb128(OS, WASM_TYPE_ANYFUNC, "table type");
   writeUleb128(OS, WASM_LIMITS_FLAG_HAS_MAX, "table flags");
   writeUleb128(OS, TableSize, "table initial size");
   writeUleb128(OS, TableSize, "table max size");
 }
 
 void Writer::createExportSection() {
   bool ExportMemory = !Config->Relocatable && !Config->ImportMemory;
-  Symbol *EntrySym = Symtab->find(Config->Entry);
-  bool ExportEntry = !Config->Relocatable && EntrySym && EntrySym->isDefined();
-  bool ExportHidden = Config->EmitRelocs;
-
-  uint32_t NumExports = ExportMemory ? 1 : 0;
-
-  std::vector<const Symbol *> SymbolExports;
-  if (ExportEntry)
-    SymbolExports.emplace_back(EntrySym);
-
-  for (const Symbol *Sym : Symtab->getSymbols()) {
-    if (Sym->isUndefined() || Sym->isGlobal())
-      continue;
-    if (Sym->isHidden() && !ExportHidden)
-      continue;
-    if (ExportEntry && Sym == EntrySym)
-      continue;
-    SymbolExports.emplace_back(Sym);
-  }
 
-  for (const Symbol *Sym : DefinedGlobals) {
-    // Can't export the SP right now because it mutable and mutable globals
-    // connot be exported.
-    if (Sym == Config->StackPointerSymbol)
-      continue;
-    SymbolExports.emplace_back(Sym);
-  }
-
-  NumExports += SymbolExports.size();
+  uint32_t NumExports = (ExportMemory ? 1 : 0) + ExportedSymbols.size();
   if (!NumExports)
     return;
 
   SyntheticSection *Section = createSyntheticSection(WASM_SEC_EXPORT);
   raw_ostream &OS = Section->getStream();
 
   writeUleb128(OS, NumExports, "export count");
 
   if (ExportMemory) {
     WasmExport MemoryExport;
     MemoryExport.Name = "memory";
     MemoryExport.Kind = WASM_EXTERNAL_MEMORY;
     MemoryExport.Index = 0;
     writeExport(OS, MemoryExport);
   }
 
-  for (const Symbol *Sym : SymbolExports) {
-    DEBUG(dbgs() << "Export: " << Sym->getName() << "\n");
+  for (const WasmExportEntry &E : ExportedSymbols) {
+    DEBUG(dbgs() << "Export: " << E.Symbol->getName() << "\n");
     WasmExport Export;
-    Export.Name = Sym->getName();
-    Export.Index = Sym->getOutputIndex();
-    if (Sym->isFunction())
+    Export.Name = E.FieldName;
+    Export.Index = E.Symbol->getOutputIndex();
+    if (E.Symbol->isFunction())
       Export.Kind = WASM_EXTERNAL_FUNCTION;
     else
       Export.Kind = WASM_EXTERNAL_GLOBAL;
     writeExport(OS, Export);
   }
 }
 
 void Writer::createStartSection() {}
void Writer::createLinkingSection() {
   SubSection DataSizeSubSection(WASM_DATA_SIZE);
   writeUleb128(DataSizeSubSection.getStream(), DataSize, "data size");
   DataSizeSubSection.finalizeContents();
   DataSizeSubSection.writeToStream(OS);
 
   if (!Config->Relocatable)
     return;
 
+  std::vector<std::pair<StringRef, uint32_t>> SymbolInfo;
+  for (const WasmExportEntry &E : ExportedSymbols) {
+    uint32_t Flags =
+        (E.Symbol->isLocal() ? WASM_SYMBOL_BINDING_LOCAL :
+         E.Symbol->isWeak() ? WASM_SYMBOL_BINDING_WEAK : 0) |
+        (E.Symbol->isHidden() ? WASM_SYMBOL_VISIBILITY_HIDDEN : 0);
+    if (Flags)
+      SymbolInfo.emplace_back(E.FieldName, Flags);
+  }
+  if (!SymbolInfo.empty()) {
+    SubSection SubSection(WASM_SYMBOL_INFO);
+    writeUleb128(SubSection.getStream(), SymbolInfo.size(), "num sym info");
+    for (auto Pair: SymbolInfo) {
+      writeStr(SubSection.getStream(), Pair.first, "sym name");
+      writeUleb128(SubSection.getStream(), Pair.second, "sym flags");
+    }
+    SubSection.finalizeContents();
+    SubSection.writeToStream(OS);
+  }
+
   if (Segments.size()) {
     SubSection SubSection(WASM_SEGMENT_INFO);
     writeUleb128(SubSection.getStream(), Segments.size(), "num data segments");
     for (const OutputSegment *S : Segments) {
       writeStr(SubSection.getStream(), S->Name, "segment name");
       writeUleb128(SubSection.getStream(), S->Alignment, "alignment");
       writeUleb128(SubSection.getStream(), 0, "flags");
     }
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);
     }
   }
 }
 
+void Writer::calculateExports() {
+  Symbol *EntrySym = Symtab->find(Config->Entry);
+  bool ExportEntry = !Config->Relocatable && EntrySym && EntrySym->isDefined();
+  bool ExportHidden = Config->EmitRelocs;
+  StringSet<> UsedNames;
+  auto budgeLocalName = [&](const Symbol *Sym) {
+    StringRef SymName = Sym->getName();
+    // We can't budge non-local names.
+    if (!Sym->isLocal())
+      return SymName;
+    // We must budge local names that have a collision with a symbol that we
+    // haven't yet processed.
+    if (!Symtab->find(SymName) && UsedNames.insert(SymName).second)
+      return SymName;
+    for (unsigned i = 1; ; ++i) {
+      std::string NameBuf = (SymName + "." + Twine(i)).str();
+      if (!UsedNames.count(NameBuf)) {
+        StringRef Name = Saver.save(NameBuf);
+        UsedNames.insert(Name); // Insert must use safe StringRef from save()
+        return Name;
+      }
+    }
+  };
+
+  if (ExportEntry)
+    ExportedSymbols.emplace_back(WasmExportEntry{EntrySym, EntrySym->getName()});
+
+  if (Config->CtorSymbol && ExportHidden &&
+      !(ExportEntry && Config->CtorSymbol == EntrySym))
+    ExportedSymbols.emplace_back(
+        WasmExportEntry{Config->CtorSymbol, Config->CtorSymbol->getName()});
+
+  for (ObjFile *File : Symtab->ObjectFiles) {
+    for (Symbol *Sym : File->getSymbols()) {
+      if (!Sym->isDefined() || File != Sym->getFile())
+        continue;
+      if (Sym->isGlobal())
+        continue;
+      if (Sym->getFunction()->Discarded)
+        continue;
+
+      if ((Sym->isHidden() || Sym->isLocal()) && !ExportHidden)
+        continue;
+      if (ExportEntry && Sym == EntrySym)
+        continue;
+      ExportedSymbols.emplace_back(WasmExportEntry{Sym, budgeLocalName(Sym)});
+    }
+  }
+
+  for (const Symbol *Sym : DefinedGlobals) {
+    // Can't export the SP right now because it's mutable and mutable globals
+    // cannot be exported.
+    if (Sym == Config->StackPointerSymbol)
+      continue;
+    ExportedSymbols.emplace_back(WasmExportEntry{Sym, budgeLocalName(Sym)});
+  }
+}
+
 uint32_t Writer::lookupType(const WasmSignature &Sig) {
   auto It = TypeIndices.find(Sig);
   if (It == TypeIndices.end()) {
     error("type not found: " + toString(Sig));
     return 0;
   }
   return It->second;
 }

 
 void Writer::run() {
   log("-- calculateTypes");
   calculateTypes();
   log("-- calculateImports");
   calculateImports();
   log("-- assignIndexes");
   assignIndexes();
+  log("-- calculateExports");
+  calculateExports();
   log("-- calculateInitFunctions");
   calculateInitFunctions();
   if (!Config->Relocatable)
     createCtorFunction();
 
   if (errorHandler().Verbose) {
     log("Defined Functions: " + Twine(DefinedFunctions.size()));
     log("Defined Globals  : " + Twine(DefinedGlobals.size()));