linux-kernel - Re: [PATCH v2 1/2] riscv: introduce RISCV_EFFICIENT_UNALIGNED

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Date: Thu, 21 Dec 2023 23:04:03 -0600
From: Eric Biggers <ebiggers@...nel.org>
To: Qingfang DENG <dqfext@...il.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Conor Dooley <conor.dooley@...rochip.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jisheng Zhang <jszhang@...nel.org>
Subject: Re: [PATCH v2 1/2] riscv: introduce RISCV_EFFICIENT_UNALIGNED_ACCESS

On Tue, Dec 05, 2023 at 04:39:24PM +0800, Qingfang DENG wrote:
> Hi,
> 
> You may as well remove the -mstrict-align CFLAGS in the Makefile, if
> this option is enabled:
> 
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -108,7 +108,9 @@ KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)
>  # unaligned accesses.  While unaligned accesses are explicitly allowed in the
>  # RISC-V ISA, they're emulated by machine mode traps on all extant
>  # architectures.  It's faster to have GCC emit only aligned accesses.
> +ifneq ($(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS),y)
>  KBUILD_CFLAGS += $(call cc-option,-mstrict-align)
> +endif
>  

Agreed.  When CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y, we shouldn't use
-mstrict-align, so that the compiler can actually use unaligned memory accesses.

If I understand correctly, beyond the change requested above, people seem to be
happy with this patch.  Jisheng, can you resend it with the above feedback
addressed?  Thanks!

- Eric