linux-kernel - Re: [PATCH 1/7] usb: trivial cleanups

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Message-ID: <94a0d4530910190703q1a0e2a6ar4cf74a68d7bc339f@mail.gmail.com>
Date:	Mon, 19 Oct 2009 17:03:18 +0300
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH 1/7] usb: trivial cleanups

On Mon, Oct 19, 2009 at 4:59 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Mon, 19 Oct 2009, Felipe Contreras wrote:
>
>> I still have an unfixed warning:
>> drivers/usb/core/hcd.c: In function ‘rh_string’:
>> /data/public/src/linux/arch/x86/include/asm/string_32.h:74: warning:
>> array subscript is above array bounds
>>
>> Apparently there's a problem with the optimized memcpy for x86 with this code:
>> static char const langids[4] = {4, USB_DT_STRING, 0x09, 0x04};
>> len = min_t(unsigned, len, sizeof(langids));
>> memcpy(data, langids, len);
>> return len;
>>
>> gcc 4.4 is trying to optimize the memcpy, but it's not able to realize
>> that 'len' will always be <= 4 and the memcpy will not exceed langids.
>> One way to solve this is by replacing len with the min_t expression:
>> memcpy(data, langids, min_t(unsigned, len, sizeof(langids)));
>>
>> However, that looks ugly and we need the expression again for the
>> return. Another way is to remove 'const' from langids.
>>
>> AFAIK the code is perfectly correct as it is, I think the fact that
>> gcc 4.4 complains is a bug on gcc side.
>
> Yes, it is a well-known bug in gcc.  Other places in the kernel get
> similar warnings.

So gcc guys are aware of this? Is there a bug report or something?

-- 
Felipe Contreras
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