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Re: [PATCH] futex: make FUTEX_OP_OPARG_SHIFT unsigned

From Thomas Gleixner <tglx@linutronix.de>
Newsgroups linux.kernel
Subject Re: [PATCH] futex: make FUTEX_OP_OPARG_SHIFT unsigned
Date 2016-10-26 13:30 +0200
Message-ID <swuz7-2VL-25@gated-at.bofh.it> (permalink)
References <svKFY-6hE-35@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Mon, 24 Oct 2016, Jiri Slaby wrote:

> FUTEX_OP_OPARG_SHIFT is shifted left by 28 in futex_atomic_op_inuser and
> other places. Since FUTEX_OP_OPARG_SHIFT is 8, we actually do (8 << 28).
> But given both are ints, we perform operation with undefined behaviour
> about which UBSAN reports:
> UBSAN: Undefined behaviour in arch/x86/include/asm/futex.h:53:13
> shift exponent 776 is too large for 32-bit type 'int'

shift exponent 776 ????

Thanks,
	tglx

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[PATCH] futex: make FUTEX_OP_OPARG_SHIFT unsigned Jiri Slaby <jslaby@suse.cz> - 2016-10-24 12:30 +0200
  Re: [PATCH] futex: make FUTEX_OP_OPARG_SHIFT unsigned Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 13:30 +0200

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