Replicant

h1. PathInterposer

h2 .Warnings

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

h2. Introduction

TODO

h2. 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, here's an example of how the path looks like for applications being launched through the path interposer[1]:

<pre>

/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

</pre>

Here we can deduce that the prebuilts take precedence over the host binaries.

fn1. This has been deduced by prints with the following patch:

<pre>

--- 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 {

</pre>

h2. 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:

<pre>

MESA_PYTHON2 := out/.path/python2

MESA_PYTHON3 := out/.path/python3

</pre>

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

<pre>

$ 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

</pre>

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