Building custom kernel modules requires CONFIG_STACK_VALIDATION= in 1.4.0

[ryansch]

RancherOS Version: (ros os version)
v1.4.0
Where are you running RancherOS? (docker-machine, AWS, GCE, baremetal, etc.)
docker-machine

I have side by side attempts to build https://github.com/maK-/SimplestLKM in a container with the `kernel-headers' service enabled.

1.3.0:

# make
make -C /lib/modules/4.9.80-rancher/build M=/root/SimplestLKM modules
make[1]: Entering directory '/lib/modules/4.9.80-rancher/build'
  CC [M]  /root/SimplestLKM/hello.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /root/SimplestLKM/hello.mod.o
  LD [M]  /root/SimplestLKM/hello.ko
make[1]: Leaving directory '/lib/modules/4.9.80-rancher/build'

1.4.0:

# make
make -C /lib/modules/4.14.32-rancher2/build M=/root/SimplestLKM modules
make[1]: Entering directory '/lib/modules/4.14.32-rancher2/build'
make[2]: *** No rule to make target 'tools/objtool/objtool', needed by '/root/SimplestLKM/hello.o'.  Stop.
Makefile:1528: recipe for target '_module_/root/SimplestLKM' failed
make[1]: *** [_module_/root/SimplestLKM] Error 2
make[1]: Leaving directory '/lib/modules/4.14.32-rancher2/build'
Makefile:12: recipe for target 'default' failed
make: *** [default] Error 2

[ryansch]

This specifically prevents us from building the parallels guest tools.

[ryansch]

More information:
https://lists.debian.org/debian-knoppix/2017/01/msg00002.html

# make CONFIG_STACK_VALIDATION= works

[ryansch]

Also: https://bugzilla.redhat.com/show_bug.cgi?id=1321628

[ryansch]

Here's a functional workaround for this issue: outstand/docker-parallels-tools@6f0188f

[niusmallnan]

Yes, I also feel pain for it.

The build failure appears to have been introduced by a regression in the kernel packaging which breaks all out-of-tree-module builds. The objtool binary is no longer being included and it is required for external module builds when the kernel is compiled with CONFIG_STACK_VALIDATION=y.

[zhoubofsy]

@ryansch @niusmallnan
Kernel with CONFIG_STACK_VALIDATION, it use objtool to perform stack metadata validation on object file ("*.o") when compile third kernel modules. The objtool is generated in ./tool/objtool directory when building kernel, but there isn't objtool in RancherOS.

There are three way to eliminate influence of STACK_VALIDATAION :

1. Compile source with "CONFIG_STACK_VALIDATION=", it doesn't perform stack metadate validation
2. Copy the objtool into RancherOS and build again
3. Rebuild kernel without "STACK_VALIDATION" of "arch/Kconfig", and chose "CONFIG_UNWINDER_GUESS" instead of "CONFIG_UNWINDER_ORC" or "CONFIG_UNWINDER_FRAME_POINTER"

I recommend the first.
Edit by @niusmallnan: recommend the second.

[rootwuj]

Tested with RancherOS version- v1.4.1-rc2 with AWS.
This version can successfully build SimplestLKM.

[niusmallnan]

Backported to v1.4.1.