[Bug]: All /proc/*/exe became /apex/com.android.runtime/bin/linker64 cause oh my tmux break after tmux 3.5 released

[fornwall]

Migrated from termux/termux-app#4188, as this issue is specific to the Play Store distribution of Termux.

Problem description

Recently tmux released 3.5 and oh my tmux broken.

gpakosz/.tmux#761

After some patches it's worked on my pc, but not my android.

gpakosz/.tmux#765

Our investigation found this and may need your help.
gpakosz/.tmux#765 (comment)

Steps to reproduce the behavior.

• install tmux & oh my tmux
• run tmux new
  And then we noticed that oh my tmux is not working.

What is the expected behavior?

oh my tmux theme should working fine.

System information

• Termux application version: Termux googleplay.2024.08.29

• Android OS version:Android REL 12 aarch64

• Device model: Xiaomi Redmi K30 5G

fastfetch output:

u0_a767@localhost
-----------------
OS: Android REL 12 aarch64
Host: Xiaomi Redmi K30 5G
Kernel: Linux 4.19.113-perf-ga1b60ef832fb
Uptime: 5 days, 18 hours, 54 mins
Packages: 132 (dpkg)
Shell: fish 3.7.1
WM: Window Manager
Terminal: Termux googleplay.2024.08.29
CPU: SM7250 (8) @ 2.40 GHz
Memory: 4.19 GiB / 7.25 GiB (58%)
Swap: 2.16 GiB / 6.00 GiB (36%)
Disk (/): 2.75 GiB / 3.01 GiB (91%) - ext4 [Read-only]
Disk (/storage/emulated): 77.97 GiB / 107.04 GiB (73%) - fuse
Local IP (tun0): 172.19.0.1/30
Local IP (wlan0): 192.168.123.5/24
Locale: en_US.UTF-8

[gpakosz]

The issue is that Oh my tmux! tries to locate the tmux executable on the filesystem.

It does so by issuing a call to readink /proc/$(tmux display -p '#{pid}')/exe and the output is /apex/com.android.runtime/bin/linker64 instead of /data/data/com.termux/files/usr/bin/tmux.

[fornwall]

@gpakosz @XyLyXyRR This issue is an unfortunate consequence of Android preventing executing files not part of the APK - see https://github.com/termux-play-store/termux-exec?tab=readme-ov-file#problem-1-cannot-execute-files-not-part-of-the-apk for details.

In short, Termux on Google Play is not allowed to execute /data/data/com.termux/files/usr/bin/tmux directly, instead it executes /apex/com.android.runtime/bin/linker64 /data/data/com.termux/files/usr/bin/tmux, leading to reading the exe symlink under /proc not working as expected.

Termux on F-Droid avoids that for now by running in a backward compatibility mode by having a low targetSdkVersion - but support for that is being phased out in general, and it's not allowed when distributing apps on Google Play.

If possible, I think the best workaround here is if you could fall back to looking up tmux in the PATH by using which or command.

[gpakosz]

Interesting,

Based on this comment, this doesn't seem to apply to /proc/self/exe though?

[fornwall]

Based on gpakosz/.tmux#765 (comment), this doesn't seem to apply to /proc/self/exe though?

Due to how often checking /proc/self/exe is done, readlink(3) is hooked using LD_PRELOAD to override when /proc/self/exe is resolved.

It could perhaps be done for /proc/${PID}/exe as well, to make things work more out of the box.. Let me try it out.

[fornwall]

This should be fixed in version 1.7 of the termux-exec package (it hooks readlink(3) of /proc/$PID/exe using LD_PRELOAD, so it should work as expected).

@XyLyXyRR Could you update with pkg up and verify that it works as expected on your device?

[XyLyXyRR]

Seems fixed right now.

env | rg TMUX returns nothing, tmux is 3.5a, oh my tmux is 2c9ef1c, and run tmux new works fine.

Now sudo eza -la /proc/*/exe returns this:

lrwxrwxrwx - u0_a767  8 Oct 08:03 /proc/9073/exe -> /data/data/com.termux/files/usr/bin/fish
lrwxrwxrwx - u0_a767  8 Oct 08:03 /proc/9812/exe -> /data/data/com.termux/files/usr/bin/tmux
lrwxrwxrwx - u0_a767  8 Oct 08:03 /proc/9814/exe -> /data/data/com.termux/files/usr/bin/tmux
lrwxrwxrwx - u0_a767  8 Oct 08:03 /proc/10053/exe -> /data/data/com.termux/files/usr/bin/fish
lrwxrwxrwx - root     8 Oct 08:04 /proc/self/exe -> /data/data/com.termux/files/usr/bin/eza
lrwxrwxrwx - root     8 Oct 08:04 /proc/thread-self/exe -> /data/data/com.termux/files/usr/bin/eza

Thank you. Have a good day, guys!

[gpakosz]

Thank you @fornwall 🙏