[llvm-dev] Using LLD to create a .lib from a .def

[Andrew Kelley via llvm-dev]

I'm copying some LLD code into my codebase like this:

// workaround for LLD not exposing ability to convert .def to .lib

#include <set>

namespace lld {
namespace coff {

class SymbolBody;
class StringChunk;
struct Symbol;

struct Export {
  StringRef Name;       // N in /export:N or /export:E=N
  StringRef ExtName;    // E in /export:E=N
  SymbolBody *Sym = nullptr;
  uint16_t Ordinal = 0;
  bool Noname = false;
  bool Data = false;
  bool Private = false;

  // If an export is a form of /export:foo=dllname.bar, that means
  // that foo should be exported as an alias to bar in the DLL.
  // ForwardTo is set to "dllname.bar" part. Usually empty.
  StringRef ForwardTo;
  StringChunk *ForwardChunk = nullptr;

  // True if this /export option was in .drectves section.
  bool Directives = false;
  StringRef SymbolName;
  StringRef ExportName; // Name in DLL

  bool operator==(const Export &E) {
    return (Name == E.Name && ExtName == E.ExtName &&
            Ordinal == E.Ordinal && Noname == E.Noname &&
            Data == E.Data && Private == E.Private);
  }
};

enum class DebugType {
  None  = 0x0,
  CV    = 0x1,  /// CodeView
  PData = 0x2,  /// Procedure Data
  Fixup = 0x4,  /// Relocation Table
};

struct Configuration {
  enum ManifestKind { SideBySide, Embed, No };
  llvm::COFF::MachineTypes Machine = llvm::COFF::IMAGE_FILE_MACHINE_UNKNOWN;
  bool Verbose = false;
  llvm::COFF::WindowsSubsystem Subsystem =
llvm::COFF::IMAGE_SUBSYSTEM_UNKNOWN;
  SymbolBody *Entry = nullptr;
  bool NoEntry = false;
  std::string OutputFile;
  bool DoGC = true;
  bool DoICF = true;
  bool Relocatable = true;
  bool Force = false;
  bool Debug = false;
  bool WriteSymtab = true;
  unsigned DebugTypes = static_cast<unsigned>(DebugType::None);
  StringRef PDBPath;

  // Symbols in this set are considered as live by the garbage collector.
  std::set<SymbolBody *> GCRoot;

  std::set<StringRef> NoDefaultLibs;
  bool NoDefaultLibAll = false;

  // True if we are creating a DLL.
  bool DLL = false;
  StringRef Implib;
  std::vector<Export> Exports;
  std::set<std::string> DelayLoads;
  std::map<std::string, int> DLLOrder;
  SymbolBody *DelayLoadHelper = nullptr;

  // Used for SafeSEH.
  Symbol *SEHTable = nullptr;
  Symbol *SEHCount = nullptr;

  // Used for /opt:lldlto=N
  unsigned LTOOptLevel = 2;

  // Used for /opt:lldltojobs=N
  unsigned LTOJobs = 1;

  // Used for /merge:from=to (e.g. /merge:.rdata=.text)
  std::map<StringRef, StringRef> Merge;

  // Used for /section=.name,{DEKPRSW} to set section attributes.
  std::map<StringRef, uint32_t> Section;

  // Options for manifest files.
  ManifestKind Manifest = SideBySide;
  int ManifestID = 1;
  StringRef ManifestDependency;
  bool ManifestUAC = true;
  std::vector<std::string> ManifestInput;
  StringRef ManifestLevel = "'asInvoker'";
  StringRef ManifestUIAccess = "'false'";
  StringRef ManifestFile;

  // Used for /failifmismatch.
  std::map<StringRef, StringRef> MustMatch;

  // Used for /alternatename.
  std::map<StringRef, StringRef> AlternateNames;

  uint64_t ImageBase = -1;
  uint64_t StackReserve = 1024 * 1024;
  uint64_t StackCommit = 4096;
  uint64_t HeapReserve = 1024 * 1024;
  uint64_t HeapCommit = 4096;
  uint32_t MajorImageVersion = 0;
  uint32_t MinorImageVersion = 0;
  uint32_t MajorOSVersion = 6;
  uint32_t MinorOSVersion = 0;
  bool DynamicBase = true;
  bool AllowBind = true;
  bool NxCompat = true;
  bool AllowIsolation = true;
  bool TerminalServerAware = true;
  bool LargeAddressAware = false;
  bool HighEntropyVA = false;

  // This is for debugging.
  bool DebugPdb = false;
  bool DumpPdb = false;
};

extern Configuration *Config;

void writeImportLibrary();
void parseModuleDefs(MemoryBufferRef MB);

} // namespace coff
} // namespace lld

//=========================================================================




This is so that I can write the following user code:



// writes the output to dll_path with .dll replaced with .lib
void ZigLLDDefToLib(Buf *def_contents, Buf *dll_path) {
    lld::coff::Config = new lld::coff::Configuration;
    auto mem_buf = MemoryBuffer::getMemBuffer(buf_ptr(def_contents));
    MemoryBufferRef mbref(*mem_buf);
    lld::coff::parseModuleDefs(mbref);
    lld::coff::Config->OutputFile = buf_ptr(dll_path);
    lld::coff::writeImportLibrary();
}


Then I give it def_contents that looks like:
LIBRARY kernel32
EXPORTS
ExitProcess
GetConsoleMode
GetStdHandle
GetFileInformationByHandleEx
WriteFile
GetLastError


with dll_path set to ./zig-cache/all.dll. This generates
./zig-cache/all.lib.

The generated LLVM IR looks like:

; Function Attrs: noreturn nounwind
declare void @ExitProcess(i32) #6
; Function Attrs: nounwind
declare i1 @GetConsoleMode(i8* nonnull, i32* nonnull) #3
; Function Attrs: nounwind
declare i8* @GetStdHandle(i32) #3
; Function Attrs: nounwind
declare i1 @GetFileInformationByHandleEx(i8* nonnull, i32, i8* nonnull,
i32) #3
; Function Attrs: nounwind
declare i1 @WriteFile(i8* nonnull, i8* nonnull readonly, i32, i32*,
%OVERLAPPED*) #3
; Function Attrs: nounwind
declare i32 @GetLastError() #3

...with code you would expect to call these functions.

Then I link with
lld -NOLOGO -MACHINE:X64 -OUT:hello.exe -NODEFAULTLIB -ENTRY:_start
./zig-cache/hello.obj ./zig-cache/builtin.obj ./zig-cache/compiler_rt.obj
./zig-cache/all.lib


and I get the following errors:
./zig-cache/hello.obj: undefined symbol: ExitProcess
./zig-cache/hello.obj: undefined symbol: GetConsoleMode
./zig-cache/hello.obj: undefined symbol: GetStdHandle
./zig-cache/hello.obj: undefined symbol: GetFileInformationByHandleEx
./zig-cache/hello.obj: undefined symbol: GetLastError
./zig-cache/hello.obj: undefined symbol: WriteFile
error: link failed



1. Is there something else I need to be doing to make this work correctly?
(Note: I already tried renaming "all" to "kernel32". Ideally I could
generate 1 .lib file for all the DLL calls needed.)
2. Can LLD expose this ability directly so I don't have to copy paste a
bunch of LLD internal stuff?

Regards,
Andrew Kelley
ziglang.org
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