// See if the stack contains a function we are interested in.
	for i, f := range frames {
		if !sp.interest[f.Func] {
			continue
		}

		// Record sub-stack under frame's file/line.
		fname := canonicalizeFileName(f.File)
		file := sp.files[fname]
		if file == nil {
			file = &sourceFile{
				fname:    fname,
				lines:    map[int][]sourceInst{},
				funcName: map[int]string{},
			}
			sp.files[fname] = file