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

From: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
	Nathan Chancellor <nathan@kernel.org>,
	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>,
	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: Fri, 2 Oct 2026 13:02:26 +0200	[thread overview]
Message-ID: <c39d7d50-e527-4a72-a89f-da4a9ac3cc97@kernel.org> (raw)
In-Reply-To: <CAHmME9pDcYh5OVSqnju8VfgEXt3YBToDBbFNz_OguKA23r6stg@mail.gmail.com>

Le 02/10/2026 à 12:58, Jason A. Donenfeld a écrit :
> On Fri, Oct 2, 2026 at 12:57 PM Christophe Leroy (CS GROUP)
> <chleroy@kernel.org> wrote:
>>
>>
>> On Fri, 25 Sep 2026 22:46:32 +0100, Nathan Chancellor wrote:
>>> After a recent change in LLVM [1], builds with the random vDSO
>>> implementation, such as PowerPC and RISC-V, fail when checking the vDSO:
>>>
>>>    arch/powerpc/kernel/vdso/vdso32.so.dbg: dynamic relocations are not supported
>>>    arch/riscv/kernel/vdso/vdso.so.dbg: dynamic relocations are not supported
>>>
>>> memset() is now generated when zeroing params->reserved for some builds
>>> because LLVM has an optimization (now run in more instances) that can
>>> recognize at compile time when it is assigning a static value to a
>>> contiguous area of memory and turn that into a call to memset(). Both
>>> clang and GCC assume memset() is always available [2].
>>>
>>> [...]
>>
>> Applied, thanks!
>>
>> [1/1] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data()
>>        (no commit info)
> 
> That's not for you to apply. I'm sending this through my random tree,
> along with a handful of other things I need to fix. But I wanted to
> let this cook a bit more. I can add your reviewed-by line, though.

Sorry I messed up with 'b4 ty', I do not intent to take this patch in my 
tree.

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