[LLD] [COFF] Look for libfoo.a if foo.lib is specified, for MinGW

[mstorsjo]

Summary

This allows using #pragma comment(lib, "foo") in MinGW built code for system libraries, if built with -fms-extensions.

[mstorsjo]

As long as this is mostly intended for system libraries, we can skip the .dll.a part, and don't need to think about any static flag.

[mstorsjo]

Simplified it to only care about the case of system libraries for now. As this feature isn't available in ld.bfd and therefore not in use in the general mingw ecosystem, it might be ok to limit it to this case for now, for use with sanitizers?

[rnk]

COFF/Driver.cpp

377

I guess this could be has_extension, probably with Style::windows, as well.

383–385

How about llvm::sys::path::replace_extension?

386

Eh, saving a library name for every -defaultlib: we find in an object file is kind of a waste of memory. They're everywhere. But, this is a pre-existing problem that needs fixing, so I won't push to fix it now.

[mstorsjo]

COFF/Driver.cpp

383–385

I actually just changed it to use that, in the version I updated a few minutes earlier.

[rnk]

lgtm

[ruiu]

COFF/Driver.cpp

380–400

Please add a comment to explain this mingw-specific behavior. It might be a good thing to separate this code as a new function.

[mstorsjo]

COFF/Driver.cpp

380–400

Ok, I added more comments and split this to a separate function, before pushing.

COFF/Driver.cpp

Optional<StringRef> LinkerDriver::findFile(StringRef Filename) {
   if (Path.endswith_lower(".lib"))
     VisitedLibs.insert(sys::path::filename(Path));
   return Path;
 }
 
 // Find library file from search path.
 StringRef LinkerDriver::doFindLib(StringRef Filename) {
   // Add ".lib" to Filename if that has no file extension.
   bool HasExt = Filename.contains('.');
   if (!HasExt)
     Filename = Saver.save(Filename + ".lib");
-  return doFindFile(Filename);
+  StringRef Ret = doFindFile(Filename);
+  if (Config->MinGW && Ret == Filename && HasExt && !Filename.contains('/') &&
+      !Filename.contains('\\')) {
+    std::string LibName = "lib";
+    LibName += Filename.substr(0, Filename.rfind('.'));
+    LibName += ".dll.a";
+    StringRef LibNameRef = Saver.save(LibName);
+    StringRef Ret2 = doFindFile(LibNameRef);
+    // TODO: If the user passed -static to the MinGW frontend, we shouldn't
+    // check for .dll.a.
+    if (Ret2 != LibNameRef)
+      return Ret2;
+    LibName = "lib";
+    LibName += Filename.substr(0, Filename.rfind('.'));
+    LibName += ".a";
+    LibNameRef = Saver.save(LibName);
+    Ret2 = doFindFile(LibNameRef);
+    if (Ret2 != LibNameRef)
+      return Ret2;
+  }
+  return Ret;
 }
 
 // Resolves a library path. /nodefaultlib options are taken into
 // consideration. This never returns the same path (in that case,
 // it returns None).
 Optional<StringRef> LinkerDriver::findLib(StringRef Filename) {
   if (Config->NoDefaultLibAll)
     return None;

test/COFF/libname-mingw.test

+# RUN: mkdir -p %t/a
+# RUN: cp %p/Inputs/std64.lib %t/a/libstd64.a
+# RUN: cp %p/Inputs/std64.lib %t/a/libdynamic.dll.a
+
+# RUN: lld-link /lldmingw /out:%t.exe /entry:main /verbose \
+# RUN:   /defaultlib:std64.lib /subsystem:console %p/Inputs/hello64.obj \
+# RUN:   /libpath:%t/a 2>&1 | FileCheck %s
+
+CHECK: a{{[/\\]}}libstd64.a
+
+# RUN: lld-link /lldmingw /out:%t.exe /entry:main /verbose \
+# RUN:   /defaultlib:dynamic.lib /subsystem:console %p/Inputs/hello64.obj \
+# RUN:   /libpath:%t/a 2>&1 | FileCheck -check-prefix DYNAMIC %s
+
+DYNAMIC: a{{[/\\]}}libdynamic.dll.a