From: David Laight <david.laight.linux@gmail.com>
To: Borislav Betkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
Thomas Gleinxer <tglx@linutronix.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org
Cc: "David Laight" <david.laight.linux@gmail.com>,
"Nicolas Pitre" <npitre@baylibre.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Uwe Kleine-König" <u.kleine-koenig@baylibre.com>,
rodrigo.alencar@analog.com, jic23@kernel.org
Subject: [PATCH 1/2] lib: mul_u64_add_u64_div_u64: Fix addition of large constants
Date: Mon, 3 Aug 2026 10:47:01 +0100 [thread overview]
Message-ID: <20260803094702.3852-2-david.laight.linux@gmail.com> (raw)
In-Reply-To: <20260803094702.3852-1-david.laight.linux@gmail.com>
Adding constants over 2^31 fails to compile because the ADD instruction
only supports 32bit signed immediates.
Replace the "irm" constraint with "erm" so that the compiler loads
large constants into a register.
Found by a patch to drivers/iio/frequency/ad9910.c
Fixes: 6480241f31f5 ("lib: add mul_u64_add_u64_div_u64() and mul_u64_u64_div_u64_roundup()")
Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
arch/x86/include/asm/div64.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/div64.h b/arch/x86/include/asm/div64.h
index 30fd06ede751..8a2d343f977e 100644
--- a/arch/x86/include/asm/div64.h
+++ b/arch/x86/include/asm/div64.h
@@ -111,7 +111,7 @@ static inline u64 mul_u64_add_u64_div_u64(u64 rax, u64 mul, u64 add, u64 div)
if (!statically_true(!add))
asm ("addq %[add], %[lo]; adcq $0, %[hi]" :
- [lo] "+r" (rax), [hi] "+r" (rdx) : [add] "irm" (add));
+ [lo] "+r" (rax), [hi] "+r" (rdx) : [add] "erm" (add));
asm ("divq %[div]" : "+a" (rax), "+d" (rdx) : [div] "rm" (div));
--
2.39.5
next prev parent reply other threads:[~2026-08-03 9:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-03 9:47 [PATCH 0/2] x86: Use "er" asm constriant for add/sub David Laight
2026-08-03 9:47 ` David Laight [this message]
2026-08-03 10:08 ` [PATCH 1/2] lib: mul_u64_add_u64_div_u64: Fix addition of large constants H. Peter Anvin
2026-08-03 9:47 ` [PATCH 2/2] x86/local: local_add/local_sub: Support large immediate values David Laight
2026-08-03 10:01 ` Peter Zijlstra
2026-08-03 10:07 ` H. Peter Anvin
2026-08-03 9:59 ` [PATCH 0/2] x86: Use "er" asm constriant for add/sub Peter Zijlstra
2026-08-03 14:49 ` Nicolas Pitre
2026-08-03 15:39 ` David Laight
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