Re: [PATCH v2] sched: move stack_canary to the start of the randomizable region

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Nov 12, 2026 at 05:33:16AM -0800, Ron Economos wrote:

> > ---
> > From: Peter Zijlstra <peterz@infradead.org>
> > Date: Fri, 6 Nov 2026 17:07:30 +0100
> > Subject: [PATCH] riscv, sched: move stack_canary to thread_info
> > 
> > task_struct keeps growing over time. On architectures that compute the
> > per-task stack canary offset from asm-offsets.h and pass it to the
> > compiler via -mstack-protector-guard-offset=, this growth eventually
> > pushes stack_canary beyond what the target ISA can encode.
> > 
> > On RISC-V, canary loads are emitted as
> > 
> >      ld	t0, TSK_STACK_CANARY(tp)
> > 
> > where TSK_STACK_CANARY must fit into a 12-bit signed immediate, i.e.
> > [-2048, 2047].  Once stack_canary sits past byte 2047 of task_struct,
> > the build fails with
> > 
> >      cc1: error: '<N>' is not a valid offset in
> > 	'-mstack-protector-guard-offset='
> > 
> > On RISC-V, CONFIG_STACKPROTECTOR_PER_TASK depends on !RANDSTRUCT, thus
> > stack_canary does not benefit from being in the task_struct randomized
> > region.
> > 
> > Move the RISC-V stack_canary to thread_info, and introduce an access macro
> > to point to the right stack_canary location. Other archs are unaffected.
> > 
> > Not-signed-off-by: Ruidong Tian <tianruidong@linux.alibaba.com>

Signed-off-by: Peter Zijlstra <peterz@infradead.org>

> > Signed-off-by: Valentin Schneider <vschneid@redhat.com>
> > ---

> 
> I'm seeing this build failure on RISC-V with gcc 16 and
> CONFIG_SCHED_CLASS_EXT=y. The build does not fail with gcc 14. I've tested
> the proposed patch with gcc 16 and it builds and boots (on real hardware)
> just fine. So for what it's worth:
> 
> Tested-by: Ron Economos <re@w6rz.net>
> 
> Also re-adding the RISC-V folks.

Hmm, they went walk-about? Do they need a re-sent? I'm thinking this out
to perhaps go through their tree, given they're actually seeing the
problem.