Re: [PATCH v2 2/2] arch/riscv: Add bitrev.h file to support rev8 and brev8

From: Yury Norov <ynorov@nvidia.com>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Jinjie Ruan <ruanjinjie@huawei.com>,
	yury.norov@gmail.com, pjw@kernel.org, palmer@dabbelt.com,
	aou@eecs.berkeley.edu, alex@ghiti.fr, linux@rasmusvillemoes.dk,
	arnd@arndb.de, cp0613@linux.alibaba.com,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org
Subject: Re: [PATCH v2 2/2] arch/riscv: Add bitrev.h file to support rev8 and brev8
Date: Thu, 16 Apr 2026 20:34:28 -0400	[thread overview]
Message-ID: <aeF5Q2XauRKBDssy@yury> (raw)
In-Reply-To: <20260416231441.GA12905@ax162>

On Thu, Apr 16, 2026 at 04:14:41PM -0700, Nathan Chancellor wrote:
> On Wed, Apr 15, 2026 at 05:38:27PM +0800, Jinjie Ruan wrote:
> > The RISC-V Bit-manipulation Extension for Cryptography (Zbkb) provides

...

> > +static __always_inline __attribute_const__ u32 __arch_bitrev32(u32 x)
> > +{
> > +	unsigned long result = x;
> > +
> > +	if (!riscv_has_extension_likely(RISCV_ISA_EXT_ZBKB))
> > +		return generic___bitrev32(x);

Hi Nathan,

> This breaks the build when CONFIG_HAVE_ARCH_BITREVERSE is set because
> generic___bitrev32() ultimately calls generic___bitrev8(), which uses
> byte_rev_table but that is only included in lib/bitrev.c when
> CONFIG_HAVE_ARCH_BITREVERSE is not set. How was this tested? This seems
> a pretty basic build problem that has showed up in a variety of
> configurations (at least all the configurations that our CI tests).
> 
>   $ make -skj"$(nproc)" ARCH=riscv CROSS_COMPILE=riscv64-linux- mrproper defconfig all
>   ERROR: modpost: "byte_rev_table" [lib/zlib_deflate/zlib_deflate.ko] undefined!
>   ERROR: modpost: "byte_rev_table" [drivers/net/ethernet/spacemit/k1_emac.ko] undefined!
>   ERROR: modpost: "byte_rev_table" [drivers/net/ethernet/stmicro/stmmac/stmmac.ko] undefined!
> 
>   https://github.com/ClangBuiltLinux/continuous-integration2/actions/runs/24529356842
>   https://lore.kernel.org/177635154368.6552.7060101263009785041@8692ffc4d55e/

> Yury, are you intending to send this series to Linus in the 7.1 merge
> window?

No, I'm already done with this merge window. This is the material for
the next one, if ever.

Just as said, I added this one for testing. I am so far have no feedback
from robots. But your report is enough to drop it.

> If not, it shouldn't be in -next at this point.

What for do we need -next, if not for early testing?

Thanks,
Yury

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