Date: Mon, 06 Apr 2015 21:53:36 +0200 From: Jeroen Hofstee <freebsd_arm@myspectrum.nl> To: Olivier Houchard <mlfbsd@ci0.org>, Rui Paulo <rpaulo@me.com> Cc: freebsd-arm@freebsd.org Subject: Re: remove broken lib/libc/arm/string/memcpy_xscale.S Message-ID: <5522E440.3010306@myspectrum.nl> In-Reply-To: <20150406194007.GA64433@ci0.org> References: <20150405015245.GO51048@funkthat.com> <20150406171248.GV51048@funkthat.com> <20150406174130.GA63423@ci0.org> <3427080.JV46itjP9L@akita> <20150406194007.GA64433@ci0.org>
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Hi,
On 06-04-15 21:40, Olivier Houchard wrote:
> On Mon, Apr 06, 2015 at 11:32:25AM -0700, Rui Paulo wrote:
>> On Monday 06 April 2015 19:41:30 Olivier Houchard wrote:
>>> On Mon, Apr 06, 2015 at 10:12:48AM -0700, John-Mark Gurney wrote:
>>>> Warner Losh wrote this message on Mon, Apr 06, 2015 at 09:58 -0600:
>>>>>> On Apr 4, 2015, at 7:52 PM, John-Mark Gurney <jmg@funkthat.com> wrote:
>>>>>>
>>>>>> I would like to remove this file as it does not implement our defined
>>>>>> memcpy. Per POSIX, overlapping regions passed to memcpy is undefined
>>>>>> behavior. We have defined it to have the same symatics as memmove.
>>>>>>
>>>>>> Sample test program:
>>>>>> #include <stdio.h>
>>>>>> #include <string.h>
>>>>>>
>>>>>> char bufa[512] = "this is a test buffer that should be copied fine.";
>>>>>> int
>>>>>> main()
>>>>>> {
>>>>>>
>>>>>> memcpy(&bufa[10], &bufa[0], strlen(&bufa[10]));
>>>>>> printf("%s\n", bufa);
>>>>>>
>>>>>> return 0;
>>>>>>
>>>>>> }
>>>>>>
>>>>>> Output on amd64 HEAD:
>>>>>> this is a this is a test buffer that should be co
>>>>>>
>>>>>> Output on old armv4 from 9.x:
>>>>>> this is a this is a thst buffethst bufhould beufh
>>>>>>
>>>>>> If you just look at the file, it is clear that the implementation does
>>>>>> not adjust the copy direction based upon pointers. We imported the
>>>>>> code from NetBSD, and NetBSD does apparently require memcpy's
>>>>>> arguments
>>>>>> to be non-overlapping.
>>>>>>
>>>>>> I'll remove the file shortly unless someone can prove to me that all
>>>>>> uses of memcpy in our tree do not depend upon our defined behavior
>>>>>> per memcpy(3)'s man page.
>>>>> Any chance you can fix this implementation instead?
>>>> I don't know arm assembly well enough, nor do I have the time to fix
>>>> it.. I am willing to test any implementations as I have access to
>>>> hardware...
>>>>
>>>> I guess I should add a test to verify that memcpy behavese like memmove
>>>> to our test suite...
>>> I think the bug is in the manpage, not the code, and we should fix it the
>>> way NetBSD did.
>> Our implementation of memcpy() allows strings to overlap, so we really
>> shouldn't be special-casing armv4.
>>
> Any use of memcpy() with overlapping strings is a bug, I fail to see why we
> should make any effort to make it work.
For what it is worth, a similar issue is discussed at
https://sourceware.org/bugzilla/show_bug.cgi?id=12518
Regards,
Jeroen
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