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

[Deepak Gupta <debug@rivosinc.com>]

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@rivosinc.com>
>> ---
>>  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