Relocating prebuilt modules

Hello there,

I am looking for some help with how to relocate prebuilt modules.
My desired workflow is:

  • prebuild modules on host
  • copy modules to a target
  • use the prebuilt modules on target through -fprebuilt-module-path.
    My attempts are failing, as it seems the absolute path to the modules when compiled is embedded in the PCMs.

Recreating the target path to prebuilt modules on the host does not look like an option, as:

  • the target path would be within a path that users do not have permissions to on the host
  • I’d rather not touch anything out of the project build tree.

Am I missing the correct way to do this?

For reference, below is a simple test-case highlighting the issue.




set -x

rm -rf build prebuilt_modules

cat << EOF > module.modulemap
module foo { header “foo.h” }
module bar { header “bar.h” }

cat << EOF > foo.h
// empty

cat << EOF > bar.h
#include “foo.h”

cat < use.c
#include “bar.h”

Prebuild modules

clang -cc1 -x c -fmodules -fno-implicit-modules module.modulemap -fmodule-name=foo -emit-module -o build/prebuilt_modules/foo.pcm
clang -cc1 -x c -fmodules -fno-implicit-modules module.modulemap -fmodule-name=bar -emit-module -o build/prebuilt_modules/bar.pcm -fprebuilt-module-path=build/prebuilt_modules

Using them in-place works fine.

clang -cc1 -x c -fmodules -fmodule-map-file=module.modulemap -fno-implicit-modules use.c -o /dev/null -fprebuilt-module-path=build/prebuilt_modules

Relocating and using fails.

mv build/prebuilt_modules prebuilt_modules
clang -cc1 -x c -fmodules -fmodule-map-file=module.modulemap -fno-implicit-modules use.c -o /dev/null -fprebuilt-module-path=prebuilt_modules

use.c:1:2: fatal error: module file ‘./build/prebuilt_modules/foo.pcm’ not found: module file not found

#include “bar.h”


use.c:1:2: note: imported by module ‘bar’ in ‘/Volumes/work/topics/modules/relocation/example/prebuilt_modules/bar.pcm’