On Tue, Sep 22, 2026 at 08:47:35AM +0200, Peter Zijlstra wrote:
> On Tue, Sep 22, 2026 at 11:20:00AM +0530, Mukesh Kumar Chaurasiya (IBM) wrote:
> > 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:)
> >
> > The label is used consistently: in ARCH_WARN_ASM itself, in the
> > bug_addr back-reference inside __BUG_ENTRY / _EMIT_BUG_ENTRY,
>
>
> > diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
> > index 23ab05438269..6cca8880660e 100644
> > --- a/arch/x86/include/asm/bug.h
> > +++ b/arch/x86/include/asm/bug.h
> > @@ -62,8 +62,9 @@ extern void __WARN_trap(struct bug_entry *bug, ...);
> > #define HAVE_ARCH_BUG_FORMAT_ARGS
> > #endif
> >
> > +#define ARCH_WARN_ASM_TRAP_LABEL "1"
> > #define __BUG_ENTRY(format, file, line, flags)
> > \
> > - "\t.long 1b - ." "\t# bug_entry::bug_addr\n" \
> > + "\t.long " ARCH_WARN_ASM_TRAP_LABEL "b - ." "\t# bug_entry::bug_addr\n"
> > \
> > __BUG_ENTRY_FORMAT(format) \
> > __BUG_ENTRY_VERBOSE(file, line) \
> > "\t.word " flags "\t# bug_entry::flags\n"
> > @@ -101,7 +102,7 @@ do {
> > \
> > "99:\n" \
> > "\t.string \"\"\n" \
> > ".popsection\n" \
> > - "1:\t " ASM_UD2 "\n" \
> > + ARCH_WARN_ASM_TRAP_LABEL ":\t " ASM_UD2 "\n" \
> > _BUG_FLAGS_ASM("99b", file, line, flags, size, "")
> >
> > #else
>
> Not really a fan of that. And I can't really tell what you're doing with
> it either. The kunit is in Rust and thus unreadable :-(
>
> I would rather you fix up is_valid_bugaddr(), some architectures seem to
> have an always true stub because of the callchains always being from the
> break instruction.
Hey Peter,
thanks for the suggestion. I will fix up the is_valid_bugaddr for
powerpc. I am not very good with other archs asm but i can do it for
ppc32 and ppc64.
Regards,
Mukesh
