ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1

[Christian Schrefl]

On 12/14/25 12:54 AM, Rudraksha Gupta wrote:
> Hello all,
> 
> 
> I have the following problem: https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/issues/2635
> 
> 
> In short, what is happening is the following:
> 
> 
> - The kernel boots and outputs via UART when I build the kernel with the following:
> 
> make LLVM=1 ARCH="$arm" CC="${CC:-gcc}"
> 
> 
> - The kernel doesn't boot and there is no output via UART when I build the kernel with the following:
> 
> make LLVM=1 ARCH="$arm"
> 
> 
> The only difference being: CC="${CC:-gcc}". Is this expected? I think this was present in the Linux kernel ever since Rust was enabled for ARMv7, and I never encountered it because postmarketOS was originally building the first way.


I've managed to the get the build setup for qemu-armv7. For some reason
I could not get past the initrd even on kernels that are supposed to work,
but I think that is unrelated (and not a kernel issue).
On the linux-next kernel I didn't get any output on the console from qemu so I
think I've reproduced the issue. Changing CONFIG_RUST=n did not change the behavior.

So I this is almost certainly a LLVM/clang issue and not a Rust issue. I'll try to
do a bit more digging, but I'm not sure how much I'll get done.

Adding the LLVM and ARM lists to this conversation.

Cheers,
Christian