Warning: the compiler differs from the one used to build the kernel | CC=clang gives more errors

Issues & Assistance
1

Hi all,

I found another post that might be related.
I get the warning in the title when I run “make” to build a kernel module:

❯ make
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: clang version 21.1.6
  You are using:           gcc (GCC) 15.2.1 20251112
  CC [M]  it87.o
gcc: error: unrecognized command-line option ‘-mstack-alignment=8’
gcc: error: unrecognized command-line option ‘-mretpoline-external-thunk’
gcc: error: unrecognized command-line option ‘-fsplit-lto-unit’
make[3]: *** [/usr/lib/modules/6.18.2-2-cachyos/build/scripts/Makefile.build:287: it87.o] Error 1
make[2]: *** [/usr/lib/modules/6.18.2-2-cachyos/build/Makefile:2016: .] Error 2
make[1]: *** [Makefile:248: __sub-make] Error 2
make: *** [Makefile:81: modules] Error 2

I also tried specifying Clang as the compiler to use:

❯ make CC=clang
  CC [M]  it87.o
it87.c:3454:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
 3454 |                 default:
      |                 ^
it87.c:3454:3: note: insert 'break;' to avoid fall-through
 3454 |                 default:
      |                 ^
      |                 break; 
1 warning generated.
ld: unrecognised emulation mode: llvm
Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 elf_iamcu i386pep i386pe elf64bpf
make[3]: *** [/usr/lib/modules/6.18.2-2-cachyos/build/scripts/Makefile.build:287: it87.o] Error 1
make[3]: *** Deleting file 'it87.o'
make[2]: *** [/usr/lib/modules/6.18.2-2-cachyos/build/Makefile:2016: .] Error 2
make[1]: *** [Makefile:248: __sub-make] Error 2
make: *** [Makefile:81: modules] Error 2

Does anyone know why I can’t build the module using make alone?

Operating System: CachyOS Linux
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.21.0
Qt Version: 6.10.1
Kernel Version: 6.18.2-2-cachyos (64-bit)
Graphics Platform: Wayland
Processors: 20 × 13th Gen Intel® Core™ i5-13600K
Memory: 16 GiB of RAM (15.4 GiB usable)
Graphics Processor 1: AMD Radeon RX 7600
Graphics Processor 2: Intel® Graphics
Manufacturer: Gigabyte Technology Co., Ltd.
Product Name: B760M GAMING X DDR4

2

Since late 2024 (starting with kernel 6.11+), CachyOS’s default linux-cachyos kernel is compiled with Clang + ThinLTO for better performance. This is intentional and recommended.
However, many out-of-tree modules (like it87, some DKMS drivers, or manual builds) assume a GCC-built kernel or don’t fully support Clang’s build environment, leading to mismatches.

3

$ ld -v
GNU ld (GNU Binutils) 2.45.1

Because it’s clang you need this linker
$ ld.lld -v
LLD 21.1.6 (compatible with GNU linkers)

Maybe you try:
$ make LLVM=1

4

This uses clang, ld.lld (LLVM linker), and integrated assembler, avoiding the ld emulation issue and unrecognized flags.If that works, it’s the cleanest fix.

If LLVM=1 Fails
Install/update full LLVM packages: sudo pacman -Syu llvm lld clang.

5

I reinstalled the LLVM packages, but it still don’t work seem to work.

❯ make LLVM=1
  CC [M]  it87.o
it87.c:3454:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
 3454 |                 default:
      |                 ^
it87.c:3454:3: note: insert 'break;' to avoid fall-through
 3454 |                 default:
      |                 ^
      |                 break; 
1 warning generated.
  MODPOST Module.symvers
  CC [M]  it87.mod.o
  CC [M]  .module-common.o
  LD [M]  it87.ko
  BTF [M] it87.ko

❯ sudo make install
mkdir -p /lib/modules/6.18.2-2-cachyos/kernel/drivers/hwmon
cp it87.ko /lib/modules/6.18.2-2-cachyos/kernel/drivers/hwmon/
depmod -a -F /proc/kallsyms 6.18.2-2-cachyos

❯ sudo modprobe it87
modprobe: ERROR: could not insert 'it87': No such device
6

The modprobe: ERROR: could not insert ‘it87’: No such device error is very common with the it87 driver and almost never means the module is broken. It usually happens for one (or more) of these reasons:

Your motherboard’s ITE Super I/O chip is a newer/unsupported variant (e.g., IT8688E, IT8695E, IT8689E, etc.). The in-kernel it87 driver only supports older chips officially. Newer ones often need parameters to “force” detection.
ACPI resource conflict — The BIOS/ACPI claims the I/O ports, blocking the driver.
The chip isn’t auto-detected properly without hints.

First, run sensors-detect (as root) to identify your chip:

sudo sensors-detect --auto

Answer YES to all prompts (it’s safe). Look for lines like:

Found unknown chip with ID 0xXXXX

or

Found 'ITE IT86xxE Super IO Sensors' (address 0xYYY, driver `to-be-written')

Then, try loading with common parameters (as root):

sudo modprobe it87 ignore_resource_conflict=1

If that fails with the same error, add a force_id (common ones for modern boards)

sudo modprobe it87 ignore_resource_conflict=1 force_id=0x8688

Other frequent IDs to test: 0x8628, 0x8622, 0x8686, 0x8695

After each successful load, run:

sensors

and check dmesg | grep it87 for clues (e.g., “Found IT86xxE chip”, voltages/fans/temps).
To make it permanent (once you find the working combo):

echo "options it87 ignore_resource_conflict=1 force_id=0xXXXX" | sudo tee /etc/modprobe.d/it87.conf
echo "it87" | sudo tee -a /etc/modules
sudo depmod -a

Reboot and test.

If That Doesn’t Work: Use the Updated Out-of-Tree Driver
The version you’re building manually is likely old and lacks support for many recent ITE chips (common on Gigabyte/Asus/MSI boards).
The best maintained fork is frankcrawford/it87 on GitHub, which adds support for chips like IT8686E/8688E/8689E/8695E and works great on Clang kernels.

There’s an AUR package: it87-dkms-git

yay -S it87-dkms-git   # or paru, etc.

Or build manually:

git clone https://github.com/frankcrawford/it87.git
cd it87
make LLVM=1
sudo make install

Alternatives If it87 Remains Stubborn

Try nct6775 module (Nuvoton chips on some boards)

sudo modprobe nct6775
sensors

Post the output of sudo sensors-detect (or at least the ITE part) and dmesg | grep it87 after trying the modprobe commands — that’ll pinpoint the exact chip and fix

7

The issue isn’t modprobe because the it87 module isn’t even listed when I run lsmod.
I think the module isn’t build or installed correctly.
But thanks for your help.
I tried building with make alone because my CPU fan wasn’t working with make dkms.

8

Does modinfo find the module?
$ sudo modinfo it87

Try loading directly
$ sudo insmod -v ./it87.ko

Perhaps you’ve to load this ‘depends’ first:
$ sudo modinfo it87 | grep depends
depends: hwmon-vid
$ sudo insmod /lib/modules/6.18.2-2-cachyos/kernel/drivers/hwmon/hwmon-vid.ko.zst
$ sudo insmod -v ./it87.ko # your compiled module

9

modinfo finds is the preinstalled one, which is outdated (I think).

❯ sudo modinfo it87
[sudo] password for linux: 
filename:       /lib/modules/6.18.2-2-cachyos/kernel/drivers/hwmon/it87.ko.zst
author:         Chris Gauthron, Jean Delvare <jdelvare@suse.de>
description:    IT8705F/IT871xF/IT872xF hardware monitoring driver
license:        GPL
name:           it87
intree:         Y
depends:        hwmon-vid
alias:          dmi*:rvn*nVIDIA*:rn*FN68PT*:
srcversion:     BC9B0FE462169CBCF80ACFF
vermagic:       6.18.2-2-cachyos SMP preempt mod_unload 
retpoline:      Y
sig_id:         PKCS#7
signer:         Build time autogenerated kernel key
sig_key:        57:77:63:AF:B8:27:39:13:2A:37:75:43:C7:EA:DA:25:0F:EF:20:70
sig_hashalgo:   sha512
signature:      30:64:02:30:76:1C:5F:04:73:C3:EB:03:B8:FF:63:22:28:25:93:02:
                15:A7:21:AC:A2:96:32:1B:F6:18:D6:7B:55:D5:07:72:53:62:E1:CE:
                CD:AB:65:CA:CC:02:D9:80:D6:54:64:0B:02:30:7C:2C:E5:D4:76:C7:
                2F:D0:6B:17:DE:B2:D4:31:DB:B3:43:5B:90:A2:DE:2A:74:1E:B6:96:
                2C:91:1B:F2:08:65:4E:01:1B:D9:43:BA:D7:36:08:20:B2:76:0A:77:
                B5:62
parm:           fix_pwm_polarity:Force PWM polarity to active high (DANGEROUS) (bool)
parm:           update_vbat:Update vbat if set else return powerup value (bool)
parm:           ignore_resource_conflict:Ignore ACPI resource conflict (bool)
parm:           force_id:Override one or more detected device ID(s) (array of ushort)
10

and so does modprobe

which still tries to load the ‘old’ one

and not the new one

which looks like a wonky install anyway.

To verify what I think happens do a dry-run:

$ sudo modprobe --dry-run -v it87