Commit ec8bf188 authored Mar 30, 2026 by Maciej W. Rozycki Committed by Thomas Bogendoerfer Apr 01, 2026

MIPS: Fix the GCC version check for `__multi3' workaround



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: ebabcf17 ("MIPS: Implement __multi3 for GCC7 MIPS64r6 builds")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601140146.hMLODc6v-lkp@intel.com/


Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # v4.15+
Reviewed-by: David Laight <david.laight.linux@gmail.com.>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

parent d62cf151

arch/mips/lib/multi3.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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_type b)
		}
		EXPORT_SYMBOL(__multi3);

		#endif /* 64BIT && CPU_MIPSR6 && GCC7 */
		#endif /* 64BIT && CPU_MIPSR6 && GCC9 */