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

From: Andreas Schwab <schwab@linux-m68k.org>
To: Nathan Chancellor <nathan@kernel.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>,
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	 Ingo Molnar <mingo@redhat.com>,  Borislav Petkov <bp@alien8.de>,
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	 "H. Peter Anvin" <hpa@zytor.com>,
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	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 11:39:43 +0200	[thread overview]
Message-ID: <87zex4ic68.fsf@linux-m68k.org> (raw)
In-Reply-To: <20260925-vdso-getrandom-avoid-memset-llvm-24-v2-1-ce640f872393@kernel.org>

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.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

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