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From: Alan Stern <stern@rowland.harvard.edu>
To: Peter Chen <peter.chen@nxp.com>
Cc: Felipe Balbi <balbi@kernel.org>,
	"pawell@cadence.com" <pawell@cadence.com>,
	"rogerq@ti.com" <rogerq@ti.com>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	dl-linux-imx <linux-imx@nxp.com>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	Jun Li <jun.li@nxp.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH 1/3] usb: cdns3: gadget: suspicious implicit sign extension
Date: Tue, 27 Oct 2020 10:21:23 -0400	[thread overview]
Message-ID: <20201027142123.GA1233346@rowland.harvard.edu> (raw)
In-Reply-To: <20201027094825.GA5940@b29397-desktop>

On Tue, Oct 27, 2020 at 09:48:54AM +0000, Peter Chen wrote:
> If you compile the code:
> 
> unsigned int k = 0x80 << 24 + 0x81;
> 
> It will report build warning:
> warning: left shift count >= width of type [-Wshift-count-overflow]

That's a separate issue.  I believe (but haven't checked) that the << 
operator has lower precedence than +, so the compiler interprets the 
expression as:

unsigned int k = 0x80 << (24 + 0x81);

and it's pretty obvious why this causes an error.  Instead, try 
compiling:

unsigned int k = (0x80 << 24) + 0x81;

You may get an error message about signed-integer overflow, but not 
about shift-count overflow.

Alan Stern

  parent reply	other threads:[~2020-10-27 14:21 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-16 10:16 [PATCH 0/3] usb: cdns3: three bug fixes for v5.10 Peter Chen
2020-10-16 10:16 ` [PATCH 1/3] usb: cdns3: gadget: suspicious implicit sign extension Peter Chen
2020-10-27  9:03   ` Felipe Balbi
2020-10-27  9:48     ` Peter Chen
2020-10-27 10:08       ` David Laight
2020-10-27 14:21       ` Alan Stern [this message]
2020-10-28  6:41         ` Peter Chen
2020-10-27  9:03   ` Felipe Balbi
2020-10-16 10:16 ` [PATCH 2/3] usb: cdns3: gadget: own the lock wrongly at the suspend routine Peter Chen
2020-10-27  9:08   ` Felipe Balbi
2020-10-27  9:08   ` Felipe Balbi
2020-10-16 10:16 ` [PATCH 3/3] usb: cdns3: Fix on-chip memory overflow issue Peter Chen
2020-10-27  9:11   ` Felipe Balbi

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