linux-kernel - Re: [PATCH v4] selftests: riscv: add misaligned access testing

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Message-ID: <c244c1d4-fef5-439e-8dfe-12c2f8910b18@rivosinc.com>
Date: Thu, 10 Jul 2025 16:29:46 +0200
From: Clément Léger <cleger@...osinc.com>
To: Andreas Schwab <schwab@...e.de>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-riscv@...ts.infradead.org, Palmer Dabbelt <palmer@...belt.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Shuah Khan <shuah@...nel.org>,
 Alexandre Ghiti <alex@...ti.fr>
Subject: Re: [PATCH v4] selftests: riscv: add misaligned access testing



On 10/07/2025 16:23, Andreas Schwab wrote:
> On Jul 10 2025, Clément Léger wrote:
> 
>> On 10/07/2025 15:53, Andreas Schwab wrote:
>>> On Jul 10 2025, Clément Léger wrote:
>>>
>>>> This selftest tests all the currently emulated instructions (except for
>>>> the RV32 compressed ones which are left as a future exercise for a RV32
>>>> user). For the FPU instructions, all the FPU registers are tested.
>>>
>>> If that didn't catch the missing sign extension that I just fixed in
>>> <https://lore.kernel.org/linux-riscv/mvmikk0goil.fsf@suse.de>, you
>>> should consider extending the tests.
>>>
>>
>> Hi Andreas, you link doesn't work and I didn't find anything about sign
>> extension except a patch you wrote for arch_cmpxg().
> 
> lore.k.o is currently down, here's the patch I have sent:
> 
> From 77c8255da24ee4fac54e2371594d7210d1ddee19 Mon Sep 17 00:00:00 2001
> From: Andreas Schwab <schwab@...e.de>
> Date: Thu, 10 Jul 2025 13:52:35 +0200
> Subject: [PATCH] riscv: traps_misaligned: properly sign extend value in
>  misaligned load handler
> 
> Add missing cast to signed long.
> 
> Signed-off-by: Andreas Schwab <schwab@...e.de>
> ---
>  arch/riscv/kernel/traps_misaligned.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index 93043924fe6c..f760e4fcc052 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -461,7 +461,7 @@ static int handle_scalar_misaligned_load(struct pt_regs *regs)
>  	}
>  
>  	if (!fp)
> -		SET_RD(insn, regs, val.data_ulong << shift >> shift);
> +		SET_RD(insn, regs, (long)(val.data_ulong << shift) >> shift);

Hi Andreas,

Nice catch, it seems like it was fixed in OpenSBI but never backported
in the kernel. As you suggested, I'll modify the test to test the sign
extension.

Thanks,

Clément

>  	else if (len == 8)
>  		set_f64_rd(insn, regs, val.data_u64);
>  	else