[ccache] [PATCH] CCACHE_BASEDIR and dependency file creation (-MD/-MMD)

[Lalit Chhabra]

Hi,

 I am creating dependency files with my gcc compile, with
 something like:
 gxx -c -MMD -MF _dep_file.d -o _out_file.o ....

 and am using CCACHE_BASEDIR to share the cache across
 different work boxes. Both _dep_file.d and _out_file.o
 are absolute paths and start with CCACHE_BASEDIR.

 Looking at the code, my understanding is that if ccache
 determines that dependencies are being created it does
 the following:
 - If -MF is not specified, ccache add "-MF _out_file.d"
 to the preprocessor args.
 - Similarly if -MQ is not specified, it adds "-MQ _out_file.o"
 to the preprocessor args.

 These arguments are also used in the hash calculation. I
 see that ccache does not seem to strip out CCACHE_BASEDIR
 from them. This seems to be the reason I am not getting any
 hits in the subsequent compiles in other work spaces.

 I have appended a patch against ccache version 3.1.7 that
 fixes this. I would appreciate if it could be reviewed (and
 hopefully incorporated into ccache).

 Thanks,
 Lalit Chhabra
 ------------------------------------------------------------------------------------
 --- ccache-3.1.7/ccache.c 2012-01-08 06:40:55.000000000 -0800
 +++ ccache-3.1.7.mod/ccache.c 2012-07-26 18:40:04.268732000 -0700
 @@ -1414,7 +1414,6 @@
 char *arg;
 dependency_filename_specified = true;
 free(output_dep);
 - args_add(dep_args, argv[i]);
 if (strlen(argv[i]) == 3) {
 /* -MF arg */
 if (i >= argc - 1) {
 @@ -1424,13 +1423,14 @@
 goto out;
 }
 arg = argv[i + 1];
 - args_add(dep_args, argv[i + 1]);
 i++;
 } else {
 /* -MFarg */
 arg = &argv[i][3];
 }
 output_dep = make_relative_path(x_strdup(arg));
 + args_add(dep_args, "-MF");
 + args_add(dep_args, output_dep);
 continue;
 }
 if (str_startswith(argv[i], "-MQ") || str_startswith(argv[i], "-MT")) {
 @@ -1726,11 +1726,13 @@
 * Add flags for dependency generation only to the preprocessor command line.
 */
 if (generating_dependencies) {
 + char *stripped_output_obj;
 + stripped_output_obj = make_relative_path(x_strdup(output_obj));
 if (!dependency_filename_specified) {
 char *default_depfile_name;
 char *base_name;

 - base_name = remove_extension(output_obj);
 + base_name = remove_extension(stripped_output_obj);
 default_depfile_name = format("%s.d", base_name);
 free(base_name);
 args_add(dep_args, "-MF");
 @@ -1740,8 +1742,9 @@

 if (!dependency_target_specified) {
 args_add(dep_args, "-MQ");
 - args_add(dep_args, output_obj);
 + args_add(dep_args, stripped_output_obj);
 }
 + free(stripped_output_obj);
 }

 if (compile_preprocessed_source_code) {
 ------------------------------------------------------------------------------------