[LLD][COFF] Add support for /noimplib

[thieta]

Summary

Mostly for compatibility reasons with link.exe this flag
makes sure we don't write a implib - not even when /implib
is also passed, that's how link.exe works.

[mstorsjo]

lld/COFF/Options.td

60

Import, not implementation

60

Also “an”, not “a”

[thieta]

Fix help text

[thieta]

lld/COFF/Options.td

60

Thanks! Fixed.

[thieta]

Remove unintentional change

[mstorsjo]

LGTM, this looks straightforward to me.

[nikic]

lld/COFF/Driver.cpp

1677

nit: Variable arg is unused and causes a warning. Should this be using arg->getValue()?

[mstorsjo]

lld/COFF/Driver.cpp

1677

I guess this should be args.hasArg(OPT_noimplib) instead.

@thieta, what happens if the user specifies -noimplib -implib:otherfile.lib? Does the last argument win (i.e. we should use args.getLastArg(OPT_implib, OPT_noimplib) and see which one was set last, or is it the case that -noimplib always trumps -implib, regardless of their respective ordering?

[thieta]

I'll take another pass after lunch - will verify what link does as well. If there is no change in functionality- can that be submitted as a NFC or should I open another review.

[mstorsjo]

In D123591#3447830, @thieta wrote:

I'll take another pass after lunch - will verify what link does as well. If there is no change in functionality- can that be submitted as a NFC or should I open another review.

Yeah if it's just a NFC change getting rid of the warning, I'd say go ahead and push without review here.

[thieta]

In D123591#3447838, @mstorsjo wrote:

In D123591#3447830, @thieta wrote:

I'll take another pass after lunch - will verify what link does as well. If there is no change in functionality- can that be submitted as a NFC or should I open another review.

Yeah if it's just a NFC change getting rid of the warning, I'd say go ahead and push without review here.

I checked and they behave the same. I pushed a NFC for the warning here https://github.com/llvm/llvm-project/commit/837d16fb4c1cb00c5d0c72a0dff543f0bd5ff770

lld/COFF/Config.h

struct Configuration {
   std::vector<Symbol *> gcroot;
 
   std::set<std::string> noDefaultLibs;
   bool noDefaultLibAll = false;
 
   // True if we are creating a DLL.
   bool dll = false;
   StringRef implib;
+  bool noimplib = false;
   std::vector<Export> exports;
   bool hadExplicitExports;
   std::set<std::string> delayLoads;
   std::map<std::string, int> dllOrder;
   Symbol *delayLoadHelper = nullptr;
 
   bool saveTemps = false;
 

lld/COFF/Driver.cpp

void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   // Handle /include
   for (auto *arg : args.filtered(OPT_incl))
     addUndefined(arg->getValue());
 
   // Handle /implib
   if (auto *arg = args.getLastArg(OPT_implib))
     config->implib = arg->getValue();
 
+  if (auto *arg = args.getLastArg(OPT_noimplib))
+    config->noimplib = true;
+
   // Handle /opt.
   bool doGC = debug == DebugKind::None || args.hasArg(OPT_profile);
   Optional<ICFLevel> icfLevel = None;
   if (args.hasArg(OPT_profile))
     icfLevel = ICFLevel::None;
   unsigned tailMerge = 1;
   bool ltoDebugPM = false;
   for (auto *arg : args.filtered(OPT_opt)) {
void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   if (auto *arg = args.getLastArg(OPT_deffile)) {
     // parseModuleDefs mutates Config object.
     parseModuleDefs(arg->getValue());
   }
 
   // Handle generation of import library from a def file.
   if (!args.hasArg(OPT_INPUT, OPT_wholearchive_file)) {
     fixupExports();
+    if (!config->noimplib)
       createImportLibrary(/*asLib=*/true);
     return;
   }
 
   // Windows specific -- if no /subsystem is given, we need to infer
   // that from entry point name.  Must happen before /entry handling,
   // and after the early return when just writing an import library.
   if (config->subsystem == IMAGE_SUBSYSTEM_UNKNOWN) {
     config->subsystem = inferSubsystem();
if (config->mingw) {
     }
   }
 
   // Windows specific -- when we are creating a .dll file, we also
   // need to create a .lib file. In MinGW mode, we only do that when the
   // -implib option is given explicitly, for compatibility with GNU ld.
   if (!config->exports.empty() || config->dll) {
     fixupExports();
-    if (!config->mingw || !config->implib.empty())
+    if (!config->noimplib && (!config->mingw || !config->implib.empty()))
       createImportLibrary(/*asLib=*/false);
     assignExportOrdinals();
   }
 
   // Handle /output-def (MinGW specific).
   if (auto *arg = args.getLastArg(OPT_output_def))
     writeDefFile(arg->getValue());
 

lld/COFF/Options.td

 def filealign : P<"filealign", "Section alignment in the output file">;
 def functionpadmin : F<"functionpadmin">;
 def functionpadmin_opt : P<"functionpadmin",
     "Prepares an image for hotpatching">;
 def guard   : P<"guard", "Control flow guard">;
 def heap    : P<"heap", "Size of the heap">;
 def ignore : P<"ignore", "Specify warning codes to ignore">;
 def implib  : P<"implib", "Import library name">;
+def noimplib : F<"noimplib">,
+    HelpText<"Don't output an import lib">;
 def lib : F<"lib">,
     HelpText<"Act like lib.exe; must be first argument if present">;
 def libpath : P<"libpath", "Additional library search path">;
 def linkrepro : Joined<["/", "-", "/?", "-?"], "linkrepro:">,
     MetaVarName<"directory">,
     HelpText<"Write repro.tar containing inputs and command to reproduce link">;
 def lldignoreenv : F<"lldignoreenv">,
     HelpText<"Ignore environment variables like %LIB%">;

lld/test/COFF/noimplib.test

+REQUIRES: x86
+RUN: mkdir -p %t-out
+RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t-out/object.obj %S/Inputs/object.s
+
+Test that /noimplib writes no .lib file
+
+RUN: rm -f %t-out/library.lib
+RUN: lld-link -dll -machine:x64 -def:%S/Inputs/named.def -out:%t-out/library.dll %t-out/object.obj -entry:f -subsystem:console /noimplib
+RUN: not test -f %t-out/library.lib
+
+Just make sure the normal stuff works and then we just add /noimplib
+
+RUN: lld-link -dll -machine:x64 -def:%S/Inputs/named.def -out:%t-out/library.dll %t-out/object.obj -entry:f -subsystem:console /implib:%t-out/nolibrary.lib
+RUN: test -f %t-out/nolibrary.lib
+
+Test that it overrides /implib as well. This is how link.exe works
+
+RUN: rm -f %t-out/nolibrary.lib
+RUN: lld-link -dll -machine:x64 -def:%S/Inputs/named.def -out:%t-out/library.dll %t-out/object.obj -entry:f -subsystem:console /implib:%t-out/nolibrary.lib /noimplib
+RUN: not test -f %t-out/nolibrary.lib