On Wed, Jan 21, 2026 at 10:52:21AM +0000, Ryan Roberts wrote:
> On 20/01/2026 23:50, kernel test robot wrote:
> > Hi Ryan,
> >
> > kernel test robot noticed the following build warnings:
> >
> > [auto build test WARNING on akpm-mm/mm-everything]
> > [also build test WARNING on linus/master v6.19-rc6 next-20260119]
> > [cannot apply to tip/sched/core kees/for-next/hardening
> > kees/for-next/execve]
> > [If your patch is applied to the wrong git tree, kindly drop us a note.
> > And when submitting patch, we suggest to use '--base' as documented in
> > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> >
> > url:
> > https://github.com/intel-lab-lkp/linux/commits/Ryan-Roberts/randomize_kstack-Maintain-kstack_offset-per-task/20260119-210329
> > base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git
> > mm-everything
> > patch link:
> > https://lore.kernel.org/r/20260119130122.1283821-4-ryan.roberts%40arm.com
> > patch subject: [PATCH v4 3/3] randomize_kstack: Unify random source across
> > arches
> > config: x86_64-allmodconfig
> > (https://download.01.org/0day-ci/archive/20260121/[email protected]/config)
> > compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project
> > 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> > reproduce (this is a W=1 build):
> > (https://download.01.org/0day-ci/archive/20260121/[email protected]/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new
> > version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <[email protected]>
> > | Closes:
> > https://lore.kernel.org/oe-kbuild-all/[email protected]/
> >
> > All warnings (new ones prefixed by >>):
> >
> >>> vmlinux.o: warning: objtool: do_syscall_64+0x2c: call to
> >>> preempt_count_add() leaves .noinstr.text section
> >>> vmlinux.o: warning: objtool: __do_fast_syscall_32+0x3d: call to
> >>> preempt_count_add() leaves .noinstr.text section
>
> Hmm, clearly Dave was correct not to rush this through... yuck. I'll take a
> look, but I guess there is no rush if this won't go into -next until shortly
> after -rc1.
Sorry, I should have checked the entry sequencing more thoroughly when I
reviewed this,.
>From a quick look, I suspect the right thing to do is to pull the call
to add_random_kstack_offset() a bit later in a few cases; after the
entry logic has run, and after instrumentation_begin() (if the arch code
uses that), such that it doesn't matter if this gets instrumented.
Considering the callers of add_random_kstack_offset(), if we did that:
* arm64 is fine as-is.
* loongarch is fine as-is.
* powerpc's system_call_exception() would need this moved after the
user_exit_irqoff(). Given that function is notrace rather than
noinstr, it looks like there are bigger extant issues here.
* riscv is fine as-is.
* s390's __do_syscall() would need this moved after
enter_from_user_mode().
* On x86:
- do_int80_emulation() is fine as-is.
- int80_emulation() is fine as-is.
- do_int80_syscall_32() would need this moved after
instrumentation_begin().
- __do_fast_syscall_32() would need this moved after
instrumentation_begin().
- do_syscall_64() would need this moved after instrumentation_begin().
Mark.
