Creating Symbolic Links in the /vendor partition

[Curt Schwaderer]

Hello - I'm building an Android 11 product and placed the application binaries and libraries in /vendor/bin and /vendor/lib. I also need to create a symbolic link in /vendor/lib  to one of the library files also in /vendor/lib. If I try to do this in an init.<product>.rc file, it will not create the symbolic link because the /vendor partition is read only.

I move the modules into /vendor/bin and /vendor/lib at build time using the COPY_FILES += macro in an aosp_<product>.mk file, but I have not found a way to create a symbolic link in the makefile.

How and when do I create symbolic links in the /vendor partition? Please provide an example if possible.

Thanks!

Curt

[Dan Willemsen]

Ah, now I understand why I'm confused -- Android 12 (and main for the last year+) doesn't allow you to use PRODUCT_COPY_FILES to install binaries and libraries: docs. This lets us verify that all of the needed libraries will be installed, among other checks. Instead, you should define a prebuilt in an Android.bp and add the name to PRODUCT_PACKAGES. Example:

in your Android.bp:

cc_prebuilt_binary {

    name: "my_binary",

    vendor: true,

    arch: {

        arm64: {

             srcs: ["arm64/my_binary"]

        },

    },

    shared_libs: ["libmylibrary"],

}

cc_prebuilt_library {

    name: "libmylibrary",

    vendor: true,

    arch: {

        arm64: {

            srcs: ["arm64/libmylibrary.so"],

        },

    },

}

If they were built with the NDK, or use other libraries, you may need to set `sdk_version: "30"` or `shared_libs: [...]` as appropriate.

Then to install symlinks like your original question, there is a `symlinks: ["foo"]` property, which if added to my_binary above, would install a "/vendor/bin/foo -> /vendor/bin/my_binary" symlink whenever my_binary is installed.

Then in your product makefile (no need to add libmylibrary, as it will get installed as a dependency):

PRODUCT_PACKAGES += my_binary

- Dan

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[Curt Schwaderer]

Thanks Dan,

We are a product manufacturer and our board vendor's build environment is Android 11 - will what you're suggesting still work on Android 11?

We have 3 already compiled C++ binaries and 12 already built .so libraries that need to be moved on top of the vendor's board to create our product.

The (libwebsockets.so.13) library is the one that needs a symbolic link. But the symlinks attribute is not legal for cc_prebuilt_library according to the documentation (I tried it anyway and did indeed get a build error). So I assume I'll have to declare it as a cc_prebuilt_binary and use the relative_install_path attribute to put it into /vendor/lib?

I haven't been able to get anything to work, so I just tried a very simple test.

1. I put an Android.bp file in the aosp/device/<company>/<product> directory with just a single file for a test. The libwebsockets.so.13 file is located at aosp/device/<company>/<product>/br_addons/lib/libwebsockets.so.13.

cc_prebuilt_binary {

  name: "arm64_zbm1_shared.so_libwebsockets",

  vendor: true,

  arch: {

    arm64: {

      srcs: ["br_addons/lib/libwebsockets.so.13"]

    },

  },

}

2. I added the following line to our aosp_zbm1.mk file:

PRODUCT_PACKAGES += arm64_zbm1_shared.so_libwebsockets

3. The image builds successfully and I flash it onto the board.

I'm expecting to see the libwebsockets.so.13 file in /vendor/bin, but it is not.

I did a recursive file find across the entire image and there is no libwebsockets.so.13 so for some reason it didn't copy it properly.

The only thing I've been able to get working is if I use the PRODUCT_COPY_FILES macro and load the files that way.

Am I doing something wrong? I've been looking through the documentation and other board build environments. The google cuttlefish uses the cc_prebuilt_binary, but it's defined a slightly different way. I tried that as well, but it didn't work either.

Thanks,

Curt

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[Curt Schwaderer]

I got a little further, but the cc_prebuilt_library doesn't work.

I am able to add the cc_prebuilt_binary into the device/<company>/<product>/Android.bp file and it does successfully copy the binary if I add "check_elf_files: false" so it won't check the binary.

cc_prebuilt_binary {

  name: "my_sw_binary",

  stem: "my_sw",

  srcs: ["addons/bin/my_sw"],

  proprietary: true,

  vendor: true,

//  shared_libs: ["libz", "libjansson", "libwebsockets", "libxml2", "libcurl", "librohc"],

  check_elf_files: false,

}

If I un-comment the shared-libs attribute above and comment out the "check_elf_files" attribute, I get an error that the libraries are not defined which is expected.

Then I add the libjansson, libwebsockets, and librohc libraries like so:

cc_prebuilt_library {

  name: "libjansson",

  stem: "libjansson",

  srcs: ["addons/lib/libjansson.so"],

  vendor: true,

//  relative_install_path: "atsc3pak",

}

cc_prebuilt_library {

  name: "libwebsockets",

  stem: "libwebsockets.so.13",

  srcs: ["addons/lib/libwebsockets.so.13"],

  vendor: true,

}

cc_prebuilt_library {

  name: "librohc",

  stem: "librohc",

  srcs: ["addons/lib/librohc.so"],

  vendor: true,

//  relative_install_path: "atsc3pak",

}

When I do this, there is a problem with the libwebsockets.so.13 library in that the build system automatically appends a ".so" suffix to the end of libwebsockets.so.13 and I can't figure out how to prevent that from happening.

The other two libraries (libjansson, librohc) don't cause any errors at build time anymore.

Then I tried another test with "check_elf_files: false" just to see if the libraries would copy.

I commented out the libwebsockets.so.13 prebuilt library definition and just included the other two.

It builds the image correctly but when I flash it, bring the board up, and look at the directories, the libjansson.so and librohc.so files are not on the board and I don't know why?

Any ideas about these two issues?

Thanks!

Curt