rtw88 in-kernel module 8821au built, but could not insert 'rtw88_8821au': Exec format error

[y52]

Hello everybody,
I tried building an in-kernel module for USB Dongle
Bus 001 Device 003: ID 2357:0120 TP-Link Archer T2U PLUS [RTL8821AU]
on my OrangePi Plus.

Armbian supplied module from aircrack-ng/rtl8812au has become aging and raises exception errors on modprobe -r.
It was deactivated :
root@orangepiplus:/etc/modprobe.d# vi blacklist-88XXau.conf 
#blacklist 88XXau

I made a fresh install of Armbian minimal image, then switched to :

root@orangepiplus:~# uname -a
Linux orangepiplus 6.15.4-edge-sunxi #1 SMP Fri Jun 27 10:13:43 UTC 2025 armv7l GNU/Linux

root@orangepiplus:/usr/src# cat /proc/version
Linux version 6.15.4-edge-sunxi (build@armbian) (arm-linux-gnueabihf-gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0, GNU ld (GNU Binutils for Ubuntu) 2.42) #1 SMP Fri Jun 27 10:13:43 UTC 2025

root@orangepiplus:/usr/src# zcat /proc/config.gz | grep CC_VERSION
CONFIG_CC_VERSION_TEXT="arm-linux-gnueabihf-gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0"
CONFIG_GCC_VERSION=130300

root@orangepiplus:/usr/src# zcat /proc/config.gz | grep STACKPROTECTOR
CONFIG_CC_HAVE_STACKPROTECTOR_TLS=y
CONFIG_STACKPROTECTOR_PER_TASK=y
CONFIG_HAVE_STACKPROTECTOR=y
CONFIG_STACKPROTECTOR=y
CONFIG_STACKPROTECTOR_STRONG=y

Headers were downloaded with armbian-config :
root@orangepiplus:/mnt/sda2/src/linux-6.15.4#
drwxr-xr-x 25 root root     4096 Aug 21 21:40 linux-headers-6.15.4-edge-sunxi

Then performed usual build process:
root@orangepiplus:/usr/src# sudo git clone --depth 1 --branch linux-6.15.y https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git

root@orangepiplus:/usr/src# sudo ln -s /usr/src/linux /lib/modules/$(uname -r)/build
root@orangepiplus:/usr/src# ls -al /lib/modules/$(uname -r)/build
lrwxrwxrwx 1 root root 14 Aug 21 22:45 /lib/modules/6.15.4-edge-sunxi/build -> /usr/src/linux

cp /boot/config-$(uname -r) /usr/src/linux/.config
sudo make olddefconfig
sudo make menuconfig

Module activated in the following tree :
│ Symbol: RTW88 [=m]                                                                                                  │   
  │ Type  : tristate                                                                                                    │   
  │ Defined at drivers/net/wireless/realtek/rtw88/Kconfig:2                                                             │   
  │   Prompt: Realtek 802.11ac wireless chips support                                                                   │   
  │   Depends on: NETDEVICES [=y] && WLAN [=y] && WLAN_VENDOR_REALTEK [=y] && MAC80211 [=m]                             │   
  │   Location:                                                                                                         │   
  │     -> Device Drivers                                                                                               │   
  │       -> Network device support (NETDEVICES [=y])                                                                   │   
  │         -> Wireless LAN (WLAN [=y])                                                                                 │   
  │           -> Realtek devices (WLAN_VENDOR_REALTEK [=y])                                                             │   
  │ (1)         -> Realtek 802.11ac wireless chips support (RTW88 [=m])       

root@orangepiplus:/usr/src/linux# grep -E 'CONFIG_RTW88_CORE|CONFIG_RTLWIFI|CONFIG_RTW88_8821AU' .config
CONFIG_RTLWIFI=m
CONFIG_RTLWIFI_USB=m
# CONFIG_RTLWIFI_DEBUG is not set
CONFIG_RTW88_CORE=m
CONFIG_RTW88_8821AU=m

cp /usr/src/linux-headers-6.15.4-edge-sunxi/Module.symvers /usr/src/linux/

Then compiled with:

root@orangepiplus:/usr/src/linux# sudo make -j$(nproc) ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- M=drivers/net/wireless/realtek/rtw88
make[1]: Entering directory '/usr/src/linux/drivers/net/wireless/realtek/rtw88'
  MODPOST Module.symvers
  CC [M]  rtw88_core.mod.o
  CC [M]  .module-common.o
  CC [M]  rtw88_8822b.mod.o
  CC [M]  rtw88_8822bs.mod.o
  CC [M]  rtw88_8822bu.mod.o
  CC [M]  rtw88_8822c.mod.o
  CC [M]  rtw88_8822cs.mod.o
...

  LD [M]  rtw88_core.ko
  LD [M]  rtw88_8822b.ko
  LD [M]  rtw88_8822bs.ko
  LD [M]  rtw88_8822bu.ko
  LD [M]  rtw88_8822c.ko
  LD [M]  rtw88_8822cs.ko
  LD [M]  rtw88_8822cu.ko
  LD [M]  rtw88_8723x.ko
  LD [M]  rtw88_8723d.ko
  LD [M]  rtw88_8723ds.ko
  LD [M]  rtw88_8723du.ko
  LD [M]  rtw88_8821c.ko
  LD [M]  rtw88_8821cs.ko
  LD [M]  rtw88_8821cu.ko
  LD [M]  rtw88_88xxa.ko
  LD [M]  rtw88_8821a.ko
  LD [M]  rtw88_8821au.ko
  LD [M]  rtw88_sdio.ko
  LD [M]  rtw88_usb.ko
make[1]: Leaving directory '/usr/src/linux/drivers/net/wireless/realtek/rtw88'


root@orangepiplus:/usr/src/linux# modinfo /usr/src/linux/drivers/net/wireless/realtek/rtw88/rtw88_8821au.ko
filename:       /usr/src/linux/drivers/net/wireless/realtek/rtw88/rtw88_8821au.ko
license:        Dual BSD/GPL
description:    Realtek 802.11ac wireless 8821au/8811au driver
author:         Bitterblue Smith <rtl8821cerfe2@gmail.com>
...
alias:          usb:v0BDAp0811d*dc*dsc*dp*icFFiscFFipFFin*
depends:        rtw88_usb,rtw88_8821a
name:           rtw88_8821au
vermagic:       6.15.11 SMP mod_unload ARMv7 thumb2 p2v8 


sudo make modules_install ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-
doesn't work. Needs fixing. 
So I just copied modules to system location :

root@orangepiplus:/usr/src/linux# sudo cp /usr/src/linux/drivers/net/wireless/realtek/rtw88/*.ko /lib/modules/$(uname -r)/kernel/drivers/net/wireless/realtek/rtw88/
 

root@orangepiplus:/usr/src/linux# sudo depmod -a

But loading failed as follows :
root@orangepiplus:/usr/src/linux# sudo modprobe rtw88_8821au
modprobe: ERROR: could not insert 'rtw88_8821au': Exec format error
Aug 22 16:31:52 orangepiplus kernel: module rtw88_88xxa: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time


It appears to be a structural issue, as I also tried building out-of-kernel module from lwfinger/rtw88
I also tried building on Nanopi-r5s.
Each time  Exec format error was observed despite the module was successfully built.

Different analysis point to GCC version mismatch between kernel and build host, ABI incompatibility and subtle build failures, thus causing non-alignment with the kernel buid. Several other build flags were tried to align with the kernel, but in vain.
The root cause was not found. I am running out of options now.

Could community or development team point to correct approach building an in-kernel module on a running system in native environment ? 


PS : complementary information :
when armbian headers were downloaded with armbian-config, the following build output was observed :
/usr/lib/gcc/arm-linux-gnueabihf/12/cc1 -quiet -I ./scripts/include -I ./scripts/dtc/libfdt -imultilib . -imultiarch        
 arm-linux-gnueabihf -D _LARGEFILE_SOURCE -D _FILE_OFFSET_BITS=64 -D NO_YAML -MMD scripts/dtc/.dtc.o.d scripts/dtc/dtc.c
 -quiet -dumpdir scripts/dtc/ -dumpbase dtc.c -dumpbase-ext .c -mfloat-abi=hard -mtls-dialect=gnu -mthumb
 -mlibarch=armv7-a+fp -march=armv7-a+fp -O2 -Wall -Wmissing-prototypes -Wstrict-prototypes -std=gnu11 -fomit-frame-pointer
 -o /tmp/ccY6Z3QK.s

It may give some clues on the flags used.

 

Edited 4 hours ago by y52