Re: [PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data()

From: Nathan Chancellor <nathan@kernel.org>
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Huacai Chen <chenhuacai@kernel.org>,
	WANG Xuerui <kernel@xen0n.name>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, loongarch@lists.linux.dev,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data()
Date: Sat, 26 Sep 2026 13:19:27 +0100	[thread overview]
Message-ID: <20260926121927.GA1486962@ax162> (raw)
In-Reply-To: <87zex4ic68.fsf@linux-m68k.org>

On Sat, Sep 26, 2026 at 11:39:43AM +0200, Andreas Schwab wrote:
> On Sep 25 2026, Nathan Chancellor wrote:
> 
> > +#if __has_builtin(__builtin_memset_inline)
> > +#define memset_inline(dst, value, size) __builtin_memset_inline(dst, value, size)
> > +#elif IS_ENABLED(CONFIG_CC_HAS_OPT_INLINE_MEMSET)
> > +#define memset_inline(dst, value, size) __builtin_memset(dst, value, size)
> > +#else
> > +static inline void *memset_inline(void *dst, int value, size_t size)
> > +{
> > +	char *d = dst;
> > +
> > +	while (size--)
> > +		*d++ = value;
> > +
> > +	return d;
> > +}
> > +#endif
> > +
> 
> memset actually returns the original pointer, not the incremented one.
> Nothing uses the return value of memset_inline here, but it is
> confusing.

Whoops, good catch, I guess my fingers gave up on those last two
characters :) I will fix this for v3 once there has been some time for
further review.

-- 
Cheers,
Nathan

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