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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48722c845b8sm247112145e9.4.2026.03.30.02.46.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Mar 2026 02:46:45 -0700 (PDT) Date: Mon, 30 Mar 2026 10:46:44 +0100 From: David Laight To: "Maciej W. Rozycki" Cc: Thomas Bogendoerfer , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] MIPS: Fix the GCC version check for `__multi3' workaround Message-ID: <20260330104644.1da584e1@pumpkin> In-Reply-To: References: X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 30 Mar 2026 02:54:09 +0100 (BST) "Maciej W. Rozycki" wrote: > It was only GCC 10 that fixed a MIPS64r6 code generation issue with a > `__multi3' libcall inefficiently produced to perform 64-bit widening > multiplication while suitable machine instructions exist to do such a > calculation. The fix went in with GCC commit 48b2123f6336 ("re PR > target/82981 (unnecessary __multi3 call for mips64r6 linux kernel)"). > > Adjust our code accordingly, removing build failures such as: > > mips64-linux-ld: lib/math/div64.o: in function `mul_u64_add_u64_div_u64': > div64.c:(.text+0x84): undefined reference to `__multi3' > > with the GCC versions affected. > > Fixes: ebabcf17bcd7 ("MIPS: Implement __multi3 for GCC7 MIPS64r6 builds") > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-kbuild-all/202601140146.hMLODc6v-lkp@intel.com/ > Signed-off-by: Maciej W. Rozycki > Cc: stable@vger.kernel.org # v4.15+ Reviewed-by: David Laight --- > arch/mips/lib/multi3.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > linux-mips-multi3-gcc10.diff > Index: linux-macro/arch/mips/lib/multi3.c > =================================================================== > --- linux-macro.orig/arch/mips/lib/multi3.c > +++ linux-macro/arch/mips/lib/multi3.c > @@ -4,12 +4,12 @@ > #include "libgcc.h" > > /* > - * GCC 7 & older can suboptimally generate __multi3 calls for mips64r6, so for > + * GCC 9 & older can suboptimally generate __multi3 calls for mips64r6, so for > * that specific case only we implement that intrinsic here. > * > * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981 > */ > -#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 8) > +#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 10) > > /* multiply 64-bit values, low 64-bits returned */ > static inline long long notrace dmulu(long long a, long long b) > @@ -51,4 +51,4 @@ ti_type notrace __multi3(ti_type a, ti_t > } > EXPORT_SYMBOL(__multi3); > > -#endif /* 64BIT && CPU_MIPSR6 && GCC7 */ > +#endif /* 64BIT && CPU_MIPSR6 && GCC9 */ >