[lld-macho] Add support for .so file discovery

[keith]

Summary

While not the recommended extension on macOS .so is supported by ld64.
This mirrors that behavior.

Related report: https://github.com/bazelbuild/bazel/issues/18464

[MaskRay]

Yes, this matches ld64 :)

[tkoeppe]

Excellent news, this will make cross-platform building a little easier when using LLD. Thanks!

lld/MachO/Driver.cpp

 static std::optional<StringRef> findLibrary(StringRef name) {
   CachedHashStringRef key(name);
   auto entry = resolvedLibraries.find(key);
   if (entry != resolvedLibraries.end())
     return entry->second;
 
   auto doFind = [&] {
     if (config->searchDylibsFirst) {
-      if (std::optional<StringRef> path = findPathCombination(
-              "lib" + name, config->librarySearchPaths, {".tbd", ".dylib"}))
+      if (std::optional<StringRef> path =
+              findPathCombination("lib" + name, config->librarySearchPaths,
+                                  {".tbd", ".dylib", ".so"}))
         return path;
       return findPathCombination("lib" + name, config->librarySearchPaths,
                                  {".a"});
     }
     return findPathCombination("lib" + name, config->librarySearchPaths,
-                               {".tbd", ".dylib", ".a"});
+                               {".tbd", ".dylib", ".so", ".a"});
   };
 
   std::optional<StringRef> path = doFind();
   if (path)
     resolvedLibraries[key] = *path;
 
   return path;
 }

lld/MachO/InputFiles.cpp

if (isFramework) {
       for (StringRef dir : config->frameworkSearchPaths) {
         SmallString<128> candidate = dir;
         path::append(candidate, frameworkName);
         if (std::optional<StringRef> dylibPath =
                 resolveDylibPath(candidate.str()))
           return loadDylib(*dylibPath, umbrella);
       }
     } else if (std::optional<StringRef> dylibPath = findPathCombination(
-                   stem, config->librarySearchPaths, {".tbd", ".dylib"}))
+                   stem, config->librarySearchPaths, {".tbd", ".dylib", ".so"}))
       return loadDylib(*dylibPath, umbrella);
   }
 
   // 2. As absolute path.
   if (path::is_absolute(path, path::Style::posix))
     for (StringRef root : config->systemLibraryRoots)
       if (std::optional<StringRef> dylibPath =
               resolveDylibPath((root + path).str()))

lld/test/MachO/link-search-order.s

 # RUN:     | FileCheck --check-prefix=FRAMEWORKSEARCH -DPATH=%t %s
 
 # DYLIB: @executable_path/libhello.dylib
 # DYLIB: @executable_path/libgoodbye.dylib
 # DYLIB: /usr/lib/libSystem.dylib
 
 # DYLIBSEARCH:      searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.tbd, not found
 # DYLIBSEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.dylib, not found
+# DYLIBSEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.so, not found
 # DYLIBSEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.tbd, not found
 # DYLIBSEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.dylib, not found
 # DYLIBSEARCH:      searched [[PATH]]{{[/\\]}}libhello.dylib, found
 # DYLIBSEARCH:      searched [[PATH]]D{{[/\\]}}libgoodbye.dylib, found
 
 # ARCHIVE:     @executable_path/libhello.dylib
 # ARCHIVE-NOT: @executable_path/libgoodbye.dylib
 # ARCHIVE:     /usr/lib/libSystem.dylib
 
 # ARCHIVESEARCH:      searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.tbd, not found
 # ARCHIVESEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.dylib, not found
+# ARCHIVESEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.so, not found
 # ARCHIVESEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.a, not found
 # ARCHIVESEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.tbd, not found
 # ARCHIVESEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.dylib, not found
+# ARCHIVESEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.so, not found
 # ARCHIVESEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.a, not found
 # ARCHIVESEARCH:      searched [[PATH]]{{[/\\]}}libhello.dylib, found
 # ARCHIVESEARCH:      searched [[PATH]]A{{[/\\]}}libgoodbye.a, found
 
 # FRAMEWORKSEARCH:      searched [[PATH]]{{[/\\]}}Foo.framework{{[/\\]}}Foo.tbd, not found
 # FRAMEWORKSEARCH-NEXT: searched [[PATH]]{{[/\\]}}Foo.framework{{[/\\]}}Foo, not found
 
 .section __TEXT,__text