Re: [PATCH 03/24] alpha: select ARCH_HAS_UBSAN

Hi Magnus,

On Sat, Sep 05, 2026 at 01:15:18AM +0200, Magnus Lindholm wrote:

On Fri, Sep 4, 2026 at 10:31 PM Michael Cree [off-list ref] wrote:

quoted

On Wed, Sep 02, 2026 at 12:34:50AM +0200, Magnus Lindholm wrote:

quoted

On Tue, Sep 1, 2026 at 5:50 PM Matt Turner [off-list ref] wrote:

quoted

GCC's undefined behavior sanitizer has no architecture-specific runtime
requirements. Enable it for Alpha to allow UBSAN instrumentation of the
kernel.

I tested this patch on top of my rebased Alpha GENERIC_ENTRY patch on an
AlphaServer ES40. The kernel built and booted successfully with
CONFIG_UBSAN=y, and the UBSAN instrumentation is active.

So have I, on an XP1000 and ES45.

quoted

CONFIG_UBSAN_ALIGNMENT did expose a misaligned struct bucket_table
allocation in lib/rhashtable.c. This appears to be a generic rhashtable
allocation-alignment issue rather than an Alpha UBSAN problem.

But in my case the kernel vomited copious misaligned access reports,

Interestingly "kernel unaligned acc" in /proc/cpuinfo remained at
zero, which really makes me wonder whether these reports are all
false-positives.

Good question, had to dig deeper here,

Not false positives - real UB, but harmless, and I tracked down why.

Thanks for taking time to find the explanation. So, technical UB
but no consequence for operation.

Cheers,
Michael.