In my project, option '--sysroot' is widely used.  When I specified CCACHE_BASEDIR variable, I found ccache does not substitute this path to a relative path.  I made the following patch and it seems work well.

Index: /home/yeb/test/ccache-3.1/ccache.c
===================================================================
--- /home/yeb/test/ccache-3.1/ccache.c
+++ /home/yeb/test/ccache-3.1/ccache.c  2010-09-17 01:01:09.000000000 +0800
@@ -1365,15 +1365,6 @@ cc_process_args(struct args *orig_args,
                                continue;
                        }
                }
-               if (str_startswith(argv[i], "--sysroot=")) {
-                       free(output_dep);
-                       char *relpath = make_relative_path(x_strdup(argv[i] + 10));
-                       char *option = format("--sysroot=%s", relpath);
-                       args_add(stripped_args, option);
-                       free(relpath);
-                       free(option);
-                       continue;
-               }
                if (str_startswith(argv[i], "-Wp,")) {
                        if (str_startswith(argv[i], "-Wp,-MD,") && !strchr(argv[i] + 8, ',')) {
                                generating_dependencies = true;