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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a0018f0e79sm57015315e9.7.2026.09.27.00.02.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 27 Sep 2026 00:02:27 -0700 (PDT) Date: Sun, 27 Sep 2026 08:02:25 +0100 From: David Laight To: "Jason A. Donenfeld" Cc: Nathan Chancellor , Andreas Schwab , Andy Lutomirski , Thomas Gleixner , Theodore Ts'o , Vincenzo Frascino , Nick Desaulniers , Bill Wendling , Justin Stitt , Catalin Marinas , Will Deacon , Mark Rutland , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , 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() Message-ID: <20260927080225.37534e7c@pumpkin> In-Reply-To: References: <20260925-vdso-getrandom-avoid-memset-llvm-24-v2-1-ce640f872393@kernel.org> <87zex4ic68.fsf@linux-m68k.org> <20260926121927.GA1486962@ax162> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 26 Sep 2026 14:32:49 +0200 "Jason A. Donenfeld" wrote: > On Sat, Sep 26, 2026 at 01:19:27PM +0100, Nathan Chancellor wrote: > > 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. > > Do we even need to return a value at all? Might as well just make the > function two lines: > > + for (char *d = dst; size--;) > + *d++ = value; Wouldn't it be better to add a barrier() or similar in there to stop the compiler playing unwanted games> David > > (Technically that could even be one, but maybe that sort of golf loses > clarity. Your choice.) >