From: Peter Zijlstra <peterz@infradead.org>
To: David Laight <david.laight.linux@gmail.com>
Cc: "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,
"Nicolas Pitre" <npitre@baylibre.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Uwe Kleine-König" <u.kleine-koenig@baylibre.com>,
rodrigo.alencar@analog.com, jic23@kernel.org
Subject: Re: [PATCH 0/2] x86: Use "er" asm constriant for add/sub
Date: Mon, 3 Aug 2026 11:59:25 +0200 [thread overview]
Message-ID: <20260803095925.GF49951@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260803094702.3852-1-david.laight.linux@gmail.com>
On Mon, Aug 03, 2026 at 10:47:00AM +0100, David Laight wrote:
> The x86 instruction set only supports 32bit signed immediate values
> for add/sub.
> Replace the "ir" constraint with "er" to avoid build errors.
>
> Found by a patch that added used mul_u64_add_u64_div_u64() to
> do a rounding divide by 2^32 (perhaps not the best way to do this).
>
> A quick grep only found one other affected file.
I suppose the percpu stuff works because of __pcpu_cast_4 truncating the
value to u32 and then ignoring the whole signed/unsigned business. And
__pcpu_reg_imm_8 has "re".
next prev parent reply other threads:[~2026-08-03 9:59 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 ` [PATCH 1/2] lib: mul_u64_add_u64_div_u64: Fix addition of large constants David Laight
2026-08-03 10:08 ` 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 ` Peter Zijlstra [this message]
2026-08-03 14:49 ` [PATCH 0/2] x86: Use "er" asm constriant for add/sub Nicolas Pitre
2026-08-03 15:39 ` David Laight
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