When exploiting ar-chives make a .a file for each soruce subfolder

This is required because gcc-ar checks if an object file is already
in the archive by looking ONLY at the filename WITHOUT the path, so
it may happens that, for example, an object file named "subdir/spi.o",
already inside the archive, may be overwritten by an object file in
"anotherdir/spi.o" only because they are both named spi.o and even if
they are compiled on different directories.

Author: cmaglie

Diff for: legacy/builder/phases/linker.go

@@ -59,23 +59,38 @@ func (s *Linker) Run(ctx *types.Context) error {
 func link(ctx *types.Context, objectFiles paths.PathList, coreDotARelPath *paths.Path, coreArchiveFilePath *paths.Path, buildProperties *properties.Map) error {
 	objectFileList := strings.Join(utils.Map(objectFiles.AsStrings(), wrapWithDoubleQuotes), " ")
 
-	// If command line length is too big (> 30000 chars), try to collect the object files into an archive
-	// and use that archive to complete the build.
+	// If command line length is too big (> 30000 chars), try to collect the object files into archives
+	// and use that archives to complete the build.
 	if len(objectFileList) > 30000 {
-		objectFilesArchive := ctx.BuildPath.Join("object_files.a")
-		// Recreate the archive at every build
-		_ = objectFilesArchive.Remove()
+
+		// We must create an object file for each visited directory: this is required becuase gcc-ar checks
+		// if an object file is already in the archive by looking ONLY at the filename WITHOUT the path, so
+		// it may happen that a subdir/spi.o inside the archive may be overwritten by a anotherdir/spi.o
+		// because thery are both named spi.o.
+
 		properties := buildProperties.Clone()
-		properties.Set("archive_file", objectFilesArchive.Base())
-		properties.SetPath("archive_file_path", objectFilesArchive)
-		for _, objFile := range objectFiles {
-			properties.SetPath("object_file", objFile)
+		archives := map[string]bool{}
+		for _, object := range objectFiles {
+			archive := object.Parent().Join("objs.a")
+			if !archives[archive.String()] {
+				archives[archive.String()] = true
+				// Cleanup old archives
+				_ = archive.Remove()
+			}
+			properties.Set("archive_file", archive.Base())
+			properties.SetPath("archive_file_path", archive)
+			properties.SetPath("object_file", object)
 			_, _, err := builder_utils.ExecRecipe(ctx, properties, constants.RECIPE_AR_PATTERN, false, utils.ShowIfVerbose /* stdout */, utils.Show /* stderr */)
 			if err != nil {
 				return err
 			}
 		}
-		objectFileList = "-Wl,--whole-archive " + wrapWithDoubleQuotes(objectFilesArchive.String()) + " -Wl,--no-whole-archive"
+
+		objectFileList = ""
+		for archive := range archives {
+			objectFileList += " " + wrapWithDoubleQuotes(archive)
+		}
+		objectFileList = "-Wl,--whole-archive" + objectFileList + " -Wl,--no-whole-archive"
 	}
 
 	properties := buildProperties.Clone()