Re: [RFC] rust: kernel: Add KUnit tests for ARCH_WARN_ASM bug table emission

On Thu, Sep 24, 2026 at 01:31:42PM +0100, Mark Rutland wrote:

On Tue, Sep 22, 2026 at 11:20:00AM +0530, Mukesh Kumar Chaurasiya (IBM) wrote:

quoted

Verify that the __bug_table entry emitted by ARCH_WARN_ASM has a correct
bug_addr displacement — i.e. the arch's trap label reference resolves to
the trap instruction — by calling find_bug() with the exact virtual address
of the trap, mirroring what the real trap handler does.

To support all architectures, each arch that implements ARCH_WARN_ASM now
defines ARCH_WARN_ASM_TRAP_LABEL, a string constant naming the local label
at which the trap instruction is placed:

  x86       "1"     (ud2 at label 1:)
  powerpc   "1"     (twi at label 1:)
  riscv     "1"     (ebreak at label 1:)
  arm64     "14471" (brk placed at 14471: by __BUG_ENTRY_END)
  s390      "0"     (mc at label 0:)

I'm not a fan of exposing such a low-level implementation detail out of
the architecture code, and I don't think we should expose this.

What exactly are you trying to verify here, and why? Has there been
some _specific_ issue on powerpc that caused you to look at this?

Mark.

Hey Mark,

During implementing ARCH_WARN_ASM for rust I broke the bug entry for
powerpc so I wrote this to verify. I sent it out mainly for ppc but
few people wanted that if it needed it should be done for all archs.
So separated this thing and sent it out as an RFC to check whether
other archs want this or not.

Regards,
Mukesh