From: Peter Zijlstra <peterz@infradead.org>
To: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
tony.luck@intel.com, pawan.kumar.gupta@linux.intel.com,
pbonzini@redhat.com, chenyi.qiang@intel.com,
jithu.joseph@intel.com, alexs@kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/cpu: fix undefined behavior in bit shift for intel_detect_tlb
Date: Mon, 31 Oct 2022 13:32:40 +0100 [thread overview]
Message-ID: <Y1/AaJOcgIc/INtv@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <Y1/AAegYuyZPxH04@hirez.programming.kicks-ass.net>
On Mon, Oct 31, 2022 at 01:30:57PM +0100, Peter Zijlstra wrote:
> On Mon, Oct 31, 2022 at 07:43:40PM +0800, Gaosheng Cui wrote:
> > Shifting signed 32-bit value by 31 bits is undefined, so changing
> > significant bit to unsigned. The UBSAN warning calltrace like below:
> >
> > UBSAN: shift-out-of-bounds in arch/x86/kernel/cpu/intel.c:948:21
> > left shift of 1 by 31 places cannot be represented in type 'int'
>
> Is it really? Shouldn't -fstrict-overflow define this case?
-fno-strict-overflow that is, which implies -fwrapv which ensures 2s
complement, at which point shifting signed numbers is fully defined.
next prev parent reply other threads:[~2022-10-31 12:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-31 11:43 Gaosheng Cui
2022-10-31 12:04 ` Alex Shi
2022-10-31 12:30 ` Peter Zijlstra
2022-10-31 12:32 ` Peter Zijlstra [this message]
2022-11-01 11:48 ` cuigaosheng
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