Summary
The mac80211/backports package builds successfully on kernel 6.18 but fails to generate Module.symvers, causing all dependent modules (mt76, etc.) to fail with undefined symbol errors.
Environment
- OpenWrt target: x86_64
- Kernel version: 6.18.2 (testing)
- Package: kmod-mac80211 (backports-6.18)
- Working kernel: 6.12.62
Problem
When building mt76 against kernel 6.18, modpost fails with undefined symbols:
ERROR: modpost: "ieee80211_sta_register_airtime" [mt76.ko] undefined!
ERROR: modpost: "__ieee80211_schedule_txq" [mt76.ko] undefined!
ERROR: modpost: "ieee80211_free_hw" [mt76.ko] undefined!
[... 67+ more undefined symbols]
Root Cause
The backports build process fails to invoke modpost for kernel 6.18, resulting in an empty Module.symvers file:
Kernel 6.12 (working):
$ wc -l build_dir/.../linux-x86_64/symvers/mac80211.symvers
321 mac80211.symvers
Kernel 6.18 (broken):
$ wc -l build_dir/.../linux-x86_64/symvers/mac80211.symvers
0 mac80211.symvers
Both builds use the same backports-6.18 source tree, but:
- mac80211.ko is built successfully in both cases
- Module.symvers is generated only for kernel 6.12
- No Module.symvers files exist anywhere in the backports-6.18 build tree for kernel 6.18
Analysis
The backports build aggregates Module.symvers using:
grep -F <path> backports-6.18/./Module.symvers >> Module.symvers.tmp
However, individual module directories never generate Module.symvers because modpost is not being invoked during the kernel 6.18 build.
Investigation shows:
modpost binary exists at linux-6.18.2/scripts/mod/modpost- No
.cmd files in backports show modpost being invoked for individual modules
- The backports Makefile contains no references to modpost/MODPOST
Conclusion
Kernel 6.18 changed the module build system in a way that breaks the backports package's integration with the kernel build process. The backports Makefile or OpenWrt's patches need updating for kernel 6.18 compatibility.
Reproduction
- Configure OpenWrt for kernel 6.18 (testing)
- Build kmod-mac80211
- Attempt to build kmod-mt76
- Observe undefined symbol errors
- Check
build_dir/.../linux-x86_64/symvers/mac80211.symvers - it will be empty
Expected Behavior
Module.symvers should be generated during the mac80211 build, containing exported symbols like ieee80211_tx_status_ext, allowing dependent modules to link successfully.
Summary
The mac80211/backports package builds successfully on kernel 6.18 but fails to generate Module.symvers, causing all dependent modules (mt76, etc.) to fail with undefined symbol errors.
Environment
Problem
When building mt76 against kernel 6.18, modpost fails with undefined symbols:
Root Cause
The backports build process fails to invoke modpost for kernel 6.18, resulting in an empty Module.symvers file:
Kernel 6.12 (working):
Kernel 6.18 (broken):
Both builds use the same backports-6.18 source tree, but:
Analysis
The backports build aggregates Module.symvers using:
However, individual module directories never generate Module.symvers because modpost is not being invoked during the kernel 6.18 build.
Investigation shows:
modpostbinary exists atlinux-6.18.2/scripts/mod/modpost.cmdfiles in backports show modpost being invoked for individual modulesConclusion
Kernel 6.18 changed the module build system in a way that breaks the backports package's integration with the kernel build process. The backports Makefile or OpenWrt's patches need updating for kernel 6.18 compatibility.
Reproduction
build_dir/.../linux-x86_64/symvers/mac80211.symvers- it will be emptyExpected Behavior
Module.symvers should be generated during the mac80211 build, containing exported symbols like
ieee80211_tx_status_ext, allowing dependent modules to link successfully.