ARM toolchain statically linked binds /bin/sh

[arkanoid87]

/bin/sh is not present in Android, so you have to handle iptables manually as described in
https://github.com/wangyu-/udp2raw-tunnel/blob/master/doc/android_guide.md

By applying this patch I've been able to compile and run natively in
android using termux g++ using dynamic linking, so I have -a flag
working on Android

[wangyu-]

Sorry, can you explain further on how the patch works ?

The only differences in this patch is changed pthread_cancel to pthread_kill and bind to ::bind.

The pthread_cancel will be invoked only when --keep-rule is enabled, and doestnt affect -a. And I personally think "bind and ::bind" means the same fuction.

-a doesnt work is mainly bc of popen doesnt work correctly on android.

How does this patch make a difference for -a ?

[arkanoid87]

It is not really a patch, it is just a notification that the -a options is not working on android not because the popen is broken, but your binaries statically links a libc version of popen that tries to execute (execve syscall) /bin/sh, that is not existing on all android devices.
You can just:
strings udp2raw | grep /bin/sh
or just
strace -ff udp2raw
to find out where the problem is

What I have done to fix the problem is compiling "make dynamic" inside a termux environment, so basically compiling using arm g++ for arm architecture and linking agains local libc, and it works flawlessy.
The modification proposed is just what I had to edit to "make dynamic" using this environment.

Not sure how to fix this using the toolchain you are using to build the binary bundle, but I think a dynamic linked version could be a better choice for android.

Thank you for working on this tools

[wangyu-]

It is not really a patch, it is just a notification that the -a options is not working on android not because the popen is broken, but your binaries statically links a libc version of popen that tries to execute (execve syscall) /bin/sh, that is not existing on all android devices.

Got it, thank you for explanation.

Not sure how to fix this using the toolchain you are using to build the binary bundle, but I think a dynamic linked version could be a better choice for android.

I will try to fix this later. Or provide a dynamically linked version for android (not sure if one dynamic binary fits all android versions).