PathInterposer¶

Warnings¶

This page is a work in progress, so it might contains mistakes, inaccuracies, etc.

Introduction¶

TODO

how it works¶

During the build:

The host path is saved to out/.path_interposer_origpath
The host path is changed to a new one
The path interposer is used to access host binaries. It uses the saved path for that.

With Trisquel 8, and Replicant 11, here's an example of how the path looks like for applications being launched through the path interposer¹:

/home/replicant/replicant-11/prebuilts/jdk/jdk11/linux-x86/bin
/home/replicant/replicant-11/prebuilts/jdk/jdk11/linux-x86/bin
/home/replicant/replicant-11/out/soong/host/linux-x86/bin
/home/replicant/replicant-11/out/host/linux-x86/bin
/home/replicant/replicant-11/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9/bin
/home/replicant/replicant-11/development/scripts
/home/replicant/replicant-11/prebuilts/devtools/tools
/home/replicant/replicant-11/external/selinux/prebuilts/bin
/home/replicant/replicant-11/prebuilts/misc/linux-x86/dtc
/home/replicant/replicant-11/prebuilts/misc/linux-x86/libufdt
/home/replicant/replicant-11/prebuilts/clang/host/linux-x86/llvm-binutils-stable
/home/replicant/replicant-11/prebuilts/android-emulator/linux-x86_64
/home/replicant/replicant-11/prebuilts/asuite/acloud/linux-x86
/home/replicant/replicant-11/prebuilts/asuite/aidegen/linux-x86
/home/replicant/replicant-11/prebuilts/asuite/atest/linux-x86
/home/replicant/bin
/home/replicant/.local/bin
/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/sbin
/bin
/usr/games

Here we can deduce that the paths set by the Android build system take precedence over the host paths.

¹ This has been deduced by prints with the following patch:

--- a/cmd/path_interposer/main.go
+++ b/cmd/path_interposer/main.go
@@ -116,6 +116,10 @@ func Main(stdout, stderr io.Writer, interposer string, args []string, opts mainO
                return 1, fmt.Errorf("Failed to set PATH env: %v", err)
        }

+       fmt.Fprintln(os.Stderr, "####################################")
+       fmt.Fprintln(os.Stderr, os.Getenv("PATH"))
+       fmt.Fprintln(os.Stderr, "####################################")
+
        if config := opts.config(base); config.Log || config.Error {
                var procs []paths.LogProcess
                if opts.lookupParents != nil {

Launching host binaries without touching the prebuilts¶

In Replicant 10, we could use out/.path/python3 as python3 interpreter assuming that we enabled it in build/soong/ui/build/paths/config.go

for instance in the Mesa (external/mesa3d) Android.mk we had:

MESA_PYTHON2 := out/.path/python2
MESA_PYTHON3 := out/.path/python3

This worked because 'python2' and 'python3' were only available in the host path:

$ for path in $(echo /home/replicant/replicant-10/prebuilts/jdk/jdk9/linux-x86/bin:/home/replicant/replicant-10/prebuilts/jdk/jdk9/linux-x86/bin:/home/replicant/replicant-10/out/soong/host/linux-x86/bin:/home/replicant/replicant-10/out/host/linux-x86/bin:/home/replicant/replicant-10/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9/bin:/home/replicant/replicant-10/development/scripts:/home/replicant/replicant-10/prebuilts/devtools/tools:/home/replicant/replicant-10/external/selinux/prebuilts/bin:/home/replicant/replicant-10/prebuilts/misc/linux-x86/dtc:/home/replicant/replicant-10/prebuilts/misc/linux-x86/libufdt:/home/replicant/replicant-10/prebuilts/android-emulator/linux-x86_64:/home/replicant/replicant-10/prebuilts/asuite/acloud/linux-x86:/home/replicant/replicant-10/prebuilts/asuite/aidegen/linux-x86:/home/replicant/replicant-10/prebuilts/asuite/atest/linux-x86:/home/replicant/bin:/home/replicant/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games | sed 's#:#\n#g') ; do ls "${path}/python3" ; done
ls: cannot access '/home/replicant/replicant-10/prebuilts/jdk/jdk9/linux-x86/bin/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/jdk/jdk9/linux-x86/bin/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/out/soong/host/linux-x86/bin/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/out/host/linux-x86/bin/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9/bin/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/development/scripts/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/devtools/tools/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/external/selinux/prebuilts/bin/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/misc/linux-x86/dtc/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/misc/linux-x86/libufdt/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/android-emulator/linux-x86_64/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/asuite/acloud/linux-x86/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/asuite/aidegen/linux-x86/python3': No such file or directory
ls: cannot access '/home/replicant/replicant-10/prebuilts/asuite/atest/linux-x86/python3': No such file or directory
ls: cannot access '/home/replicant/bin/python3': No such file or directory
ls: cannot access '/home/replicant/.local/bin/python3': No such file or directory
ls: cannot access '/usr/local/sbin/python3': No such file or directory
ls: cannot access '/usr/local/bin/python3': No such file or directory
ls: cannot access '/usr/sbin/python3': No such file or directory
/usr/bin/python3
ls: cannot access '/sbin/python3': No such file or directory
ls: cannot access '/bin/python3': No such file or directory
ls: cannot access '/usr/games/python3': No such file or directory

For instance prebuilts/python/linux-x86/2.7.5/bin/python wasn't in the path.