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Date: Wed, 27 May 2026 10:01:41 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Igor Cudnik <igor@its.rel.pl>
Cc: heikki.krogerus@linux.intel.com, mika.westerberg@linux.intel.com,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] usb: acpi: fix undefined behavior in
 USB_ACPI_LOCATION_VALID
Message-ID: <2026052703-visibly-sureness-dd24@gregkh>
References: <20260526174513.15692-1-igor@its.rel.pl>
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In-Reply-To: <20260526174513.15692-1-igor@its.rel.pl>

On Tue, May 26, 2026 at 07:43:37PM +0200, Igor Cudnik wrote:
> USB_ACPI_LOCATION_VALID uses a signed left shift into the sign
> bit. Shifting a signed value into the sign bit is undefined behavior.
> Use BIT(31) instead.

SHouldn't this be UBIT(31) instead, if you were really worried about
this shift?

> 
> Found by cppcheck:
>       drivers/usb/core/usb-acpi.c:221:24: error:
>       Shifting signed 32-bit value by 31 bits is undefined behaviour

Is this really a bug?  Look at how this is used, is the generated code
"wrong"?

>       [shiftTooManyBitsSigned]
> 
> Fixes: f3ac348e6e045 ("usb: usb-acpi: Set port connect type of not connectable ports correctly")

Is this fixing a real bug?  Or just papering over a buggy tool?

thanks,

greg k-h