Re: [PATCH 02/11] riscv: update asm call site in `call_on_irq_stack` to setup correct label

[Deepak Gupta]

On Fri, Jul 25, 2025 at 03:33:51PM +0000, Sami Tolvanen wrote:
> On Thu, Jul 24, 2025 at 04:36:55PM -0700, Deepak Gupta wrote:
> > Call sites written in asm performing indirect call, they need to setup
> > label register (t2/x7) with correct label.
> >
> > Currently first kernel was compiled with `-save-temps` option and
> > normalized function signature string is captured and then placed at the
> > asm callsite.
> >
> > TODO: to write a macro wrapper with toolchain support.
> >
> > Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx>
> > ---
> >  arch/riscv/kernel/entry.S | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > index 2660faf52232..598e17e800ae 100644
> > --- a/arch/riscv/kernel/entry.S
> > +++ b/arch/riscv/kernel/entry.S
> > @@ -389,6 +389,7 @@ SYM_FUNC_START(call_on_irq_stack)
> >  	load_per_cpu t0, irq_stack_ptr, t1
> >  	li	t1, IRQ_STACK_SIZE
> >  	add	sp, t0, t1
> > +	lui t2, %lpad_hash("FvP7pt_regsE")
>
> Ah, I see. The plan is to hardcode the signatures in assembly code and
> keep them manually in sync with C code. When we implemented KCFI, we
> thought this would become extremely tedious to maintain after a while.

This is extremely tedious and not maintainable and primary reason (among
other secondary ones) to keep this patch series as RFC.

> Do you have any plans to add KCFI-style __kcfi_typeid_<function> symbols
> that would allow labels to be determined from C type signatures instead?

Yes something on similar lines. I have asked toolchain folks (Monk and Kito)
on how best to support this.

> Sami