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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Dan Carpenter' <dan.carpenter@oracle.com>,
        Denis Efremov <efremov@linux.com>
CC:     "devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
        Jes Sorensen <jes.sorensen@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Bastien Nocera <hadess@hadess.net>,
        Dmitry Vyukov <dvyukov@google.com>,
        Larry Finger <Larry.Finger@lwfinger.net>
Subject: RE: [PATCH] staging: rtl8723bs: hal: Fix memcpy calls
Thread-Topic: [PATCH] staging: rtl8723bs: hal: Fix memcpy calls
Thread-Index: AQHVd36LU5ikVLKK6EuvH5wLNYQtMKdEMyLwgAGeKE+AAAh2kA==
Date:   Tue, 1 Oct 2019 14:36:09 +0000
Message-ID: <8d2e8196cae74ec4ae20e9c23e898207@AcuMS.aculab.com>
References: <20190930110141.29271-1-efremov@linux.com>
 <37b195b700394e95aa8329afc9f60431@AcuMS.aculab.com>
 <e4051dcb-10dc-ff17-ec0b-6f51dccdb5bf@linux.com>
 <20191001135649.GH22609@kadam>
In-Reply-To: <20191001135649.GH22609@kadam>
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> From: Dan Carpenter
> Sent: 01 October 2019 14:57
> Subject: Re: [PATCH] staging: rtl8723bs: hal: Fix memcpy calls
...
> That's true for glibc memcpy() but not for the kernel memcpy().  In the
> kernel there are lots of places which do a zero size memcpy().

And probably from NULL (or even garbage) pointers.

After all a pointer to the end of an array (a + ARRAY_SIZE(a)) is valid
but must not be dereferenced - so memcpy() can't dereference it's
source address when the length is zero.

> The glibc attitude is "the standard allows us to put knives here" so
> let's put knives everywhere in the path.  And the GCC attitude is let's
> silently remove NULL checks instead of just printing a warning that the
> NULL check isn't required...  It could really make someone despondent.

gcc is the one that add knives...

This reminds me of me of a compiler that decided to optimise away
checks for function addresses being NULL.
At almost exactly the same time that ELF allowed for undefined weak symbols.
Checking whether a function was actually present was non-trivial.

	David

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