[llvm-dlltool] Write correct weak externals

[mstorsjo]

Summary

Previously, the created object files for the import library were broken. Write the symbol table before the string table. Simplify the code by using a separate variable Prefix instead of duplicating a few lines.

Also update the coff-weak-exports to actually check that the generated weak symbols can be found as intended.

[martell]

Indeed, the string table should be written afterwards, thanks martin.
Feel free to add aarch64 to the frontend if you are using llvm-dlltool for wine.
I saw your mingw-w64 PATCH earlier to enable arm when using dlltool.

Anyway LGTM

@hans can I request a back port of this to 5.0 once rui approves and it lands in trunk.

[mstorsjo]

In D36065#825554, @martell wrote:

Indeed, the string table should be written afterwards, thanks martin.
Feel free to add aarch64 to the frontend if you are using llvm-dlltool for wine.
I saw your mingw-w64 PATCH earlier to enable arm when using dlltool.

Not using it for wine, but I'll try to use it for mingw/arm64. I'll send a patch for hooking that up once I've got something worth showing there :-)

[ruiu]

LGTM

lib/Object/COFFImportFile.cpp

548 ↗

(On Diff #108841)

Use std::string instead of StringRef to avoid use of str().

[mstorsjo]

lib/Object/COFFImportFile.cpp

548 ↗

(On Diff #108841)

I thought about that, but then the append() below would mutably alter it - str() intentionally gives a new mutable temporary for each of the append()s here.

[ruiu]

lib/Object/COFFImportFile.cpp

548 ↗

(On Diff #108841)

Then a more natural way of doing it is (Prefix + Sym).str() instead of Prefix.str().append(Sym).

[mstorsjo]

lib/Object/COFFImportFile.cpp

548 ↗

(On Diff #108841)

Thanks - that does work.

[mstorsjo]

Using the (Prefix + Sym).str() syntax as suggested by Rui. (With Prefix still being a StringRef - or would it be preferred to make that a std::string?)

[ruiu]

LGTM

lib/Object/COFFImportFile.cpp

549 ↗

(On Diff #108882)

Please keep it in 80 cols.

[hans]

In D36065#825554, @martell wrote:

@hans can I request a back port of this to 5.0 once rui approves and it lands in trunk.

Rui: OK to merge to 5.0?

llvm/trunk/lib/Object/COFFImportFile.cpp

coff_symbol16 SymbolTable[NumberOfSymbols] = {
        u16(0),
        IMAGE_SYM_CLASS_WEAK_EXTERNAL,
        1},
       {{{2, 0, 0, 0, 3, 0, 0, 0}}, u32(0), u16(0), u16(0), uint8_t(0), 0},
   };
   SymbolTable[2].Name.Offset.Offset = sizeof(uint32_t);
 
   //__imp_ String Table
-  if (Imp) {
-    SymbolTable[3].Name.Offset.Offset = sizeof(uint32_t) + Sym.size() + 7;
-    writeStringTable(Buffer, {std::string("__imp_").append(Sym),
-                              std::string("__imp_").append(Weak)});
-  } else {
-    SymbolTable[3].Name.Offset.Offset = sizeof(uint32_t) + Sym.size() + 1;
-    writeStringTable(Buffer, {Sym, Weak});
-  }
+  StringRef Prefix = Imp ? "__imp_" : "";
+  SymbolTable[3].Name.Offset.Offset =
+      sizeof(uint32_t) + Sym.size() + Prefix.size() + 1;
   append(Buffer, SymbolTable);
+  writeStringTable(Buffer, {(Prefix + Sym).str(),
+                            (Prefix + Weak).str()});
 
   // Copied here so we can still use writeStringTable
   char *Buf = Alloc.Allocate<char>(Buffer.size());
   memcpy(Buf, Buffer.data(), Buffer.size());
   return {MemoryBufferRef(StringRef(Buf, Buffer.size()), ImportName)};
 }
 
 std::error_code writeImportLibrary(StringRef ImportName, StringRef Path,

llvm/trunk/test/DllTool/coff-weak-exports.def

 ; RUN: llvm-dlltool -m i386:x86-64 --input-def %s --output-lib %t.a
-; RUN: llvm-readobj -coff-exports %t.a | FileCheck %s
+; RUN: llvm-nm %t.a | FileCheck %s
 
 LIBRARY test.dll
 EXPORTS
 TestFunction==AltTestFunction
 
-; CHECK: File: test.dll
-; CHECK: Format: COFF-x86-64
-; CHECK: Arch: x86_64
-; CHECK: AddressSize: 64bit
-; CHECK: File: test.dll
-; CHECK: Format: COFF-x86-64
-; CHECK: Arch: x86_64
-; CHECK: AddressSize: 64bit
-; CHECK: File: test.dll
-; CHECK: Format: COFF-x86-64
-; CHECK: Arch: x86_64
-; CHECK: AddressSize: 64bit
+; CHECK:      U AltTestFunction
+; CHECK-NEXT: w TestFunction
+; CHECK:      U __imp_AltTestFunction
+; CHECK-NEXT: w __imp_TestFunction