Re: [PATCH] ARM: entry: Convert IRQ handling to generic IRQ entry

On Sat, Jun 27, 2026 at 5:16 AM Jinjie Ruan <[email protected]> wrote:

> > +noinstr void arm_irq_handler(struct pt_regs *regs, int mode)
> > +{
> > +     irqentry_state_t state = irqentry_enter(regs);
> > +
> > +     /*
> > +      * mode == 1 means we came from userspace, and then we
> > +      * should just immediately switch to the irq stack.
> > +      * Then we check of we are on the thread stack. If we are
> > +      * not, then by definition we are already using the irq stack.
> > +      */
> > +     if (mode == 1 || on_thread_stack())
> > +             call_on_irq_stack(handle_arm_irq, regs);
>
> It seems that the CONFIG_VMAP_STACK Overflow Protection is missing,

I don't think so, it is checked before this point in the assembly:

+       svc_entry trace=0
+       mov     r0, sp                          @ regs
+       mov     r1, #0                          @ from kernel mode
+       bl      arm_irq_handler
(...)

svc_entry checks it.

> should we implement the C version of CONFIG_VMAP_STACK first, before
> moving the IRQ handling to C?"

Not 100% sure what you mean here.

Currently the CONFIG_VMAP_STACK checks are done in
arch/arm/kernel/entry-armv.S, in the svc_entry macro
that is called in every exception entry.

svc_entry in turn calls do_overflow_check from
arch/arm/kernel/entry-header.S that does the actual overflow
check and calls __bad_stack() if we get an overflow.

This looks nice to have in assembly to me, and even
arm64 does this check in assembly?

How do you imagine C doing this without using any stack?

Yours,
Linus Walleij