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| From | Noob <root@127.0.0.1> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: UB of memcpy(NULL, NULL, 0) |
| Date | 2016-10-13 17:49 +0200 |
| Organization | A noiseless patient Spider |
| Message-ID | <ntoado$rdm$1@dont-email.me> (permalink) |
| References | <ntnodu$p8o$1@dont-email.me> <ntnp5r$rob$1@dont-email.me> <1bh98ggwd0.fsf@pfeifferfamily.net> |
On 13/10/2016 16:24, Joe Pfeiffer wrote:
> Richard Heathfield <rjh@cpax.org.uk> writes:
>
>> On 13/10/16 11:42, Noob wrote:
>>> Hello everyone,
>>>
>>> I've just stumbled across this article:
>>>
>>> memcpy (and friends) with NULL pointers
>>> https://www.imperialviolet.org/2016/06/26/nonnull.html
>>>
>>> which discusses an example of compiler optimization
>>> in the face of undefined behavior. Namely:
>>>
>>> #include <stdint.h>
>>> #include <string.h>
>>>
>>> int f(uint8_t *dest, uint8_t *src, size_t len) {
>>> memcpy(dest, src, len);
>>> return dest == NULL;
>>> }
>>>
>>> would remove the comparison, and unconditionally return 0.
>>
>> The compiler's behaviour is both legal and reasonable. The test is in
>> the wrong place.
>>
>>> This is similar to the bug found in Linux where someone
>>> dereferenced a pointer, and only later tested for NULL,
>>> and gcc removed the test.
>>
>> Fair enough. If the dereference is legitimate, the test is
>> pointless. And if the dereference is illegitimate, all bets are off -
>> the code is broken. Either way, gcc is correct, and the bug is in the
>> positioning of the test, not the compiler's removal thereof.
>
> It really seems like both of these are things that ought to result in a
> diagnostic. If the compiler can conclude a conditional that a
> programmer presumably thought was needed in fact isn't, it would be nice
> to inform the programmer of that fact....
Which reminds me of the thread David started in gcc-help.
https://www.spinics.net/lists/gcchelp/thrd2.html#44485
Regards.
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UB of memcpy(NULL, NULL, 0) Noob <root@127.0.0.1> - 2016-10-13 12:42 +0200
Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-13 11:55 +0100
Re: UB of memcpy(NULL, NULL, 0) Noob <root@127.0.0.1> - 2016-10-13 13:09 +0200
Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-13 12:22 +0100
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-13 12:22 -0700
Re: UB of memcpy(NULL, NULL, 0) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-10-13 12:32 -0700
Re: UB of memcpy(NULL, NULL, 0) "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-10-13 12:34 -0700
Re: UB of memcpy(NULL, NULL, 0) Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2016-10-13 08:24 -0600
Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-13 16:22 +0100
Re: UB of memcpy(NULL, NULL, 0) Noob <root@127.0.0.1> - 2016-10-13 17:49 +0200
Re: UB of memcpy(NULL, NULL, 0) Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2016-10-13 12:02 -0600
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-15 20:56 +0200
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-15 12:52 -0700
Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-15 15:55 -0400
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-15 13:41 -0700
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-16 11:17 +0200
Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-16 10:26 +0100
Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-16 09:55 +0000
Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-16 08:44 -0400
Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 10:06 +0200
Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-17 09:06 -0400
Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 16:29 +0200
Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-17 17:05 -0400
Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-18 11:19 +0200
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 08:04 -0700
Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-18 16:27 -0400
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 08:59 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-17 11:21 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 13:42 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-17 14:46 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 15:52 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-17 16:43 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 08:00 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-18 09:14 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 09:43 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-18 11:31 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 12:49 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-18 12:03 -0700
Re: UB of memcpy(NULL, NULL, 0) Jerry Stuckle <jstucklex@attglobal.net> - 2016-10-17 17:06 -0400
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 14:55 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-16 11:23 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-17 08:49 -0700
Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-18 16:54 +0000
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-18 11:09 -0700
Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-23 13:24 +0000
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 09:28 -0700
Re: UB of memcpy(NULL, NULL, 0) <william@wilbur.25thandClement.com> - 2016-10-29 11:32 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-29 14:12 -0700
Re: UB of memcpy(NULL, NULL, 0) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-15 22:00 +0100
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-16 02:51 -0700
Re: UB of memcpy(NULL, NULL, 0) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-16 11:20 +0100
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-16 04:14 -0700
Re: UB of memcpy(NULL, NULL, 0) BartC <bc@freeuk.com> - 2016-10-16 12:22 +0100
Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-16 13:01 +0100
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-16 05:29 -0700
Re: UB of memcpy(NULL, NULL, 0) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-10-16 20:47 +0100
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-17 02:08 -0700
Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 10:24 +0200
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-17 08:05 -0700
Re: UB of memcpy(NULL, NULL, 0) David Brown <david.brown@hesbynett.no> - 2016-10-17 17:25 +0200
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-17 17:08 +0200
Re: UB of memcpy(NULL, NULL, 0) Lorinczy Zsigmond <zsiga@nospam.for.me> - 2016-10-21 12:46 +0200
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-21 08:06 -0700
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-21 18:30 +0200
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-21 09:34 -0700
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-22 07:42 +0200
Re: UB of memcpy(NULL, NULL, 0) James Kuyper <jameskuyper@verizon.net> - 2016-10-22 10:31 -0400
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-22 17:49 +0200
Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-22 13:43 -0700
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-23 07:47 +0200
Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-23 11:07 -0400
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-23 17:45 +0200
Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-23 12:16 -0400
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 07:38 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 08:38 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 09:44 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-23 12:22 -0700
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-23 13:37 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-23 14:15 -0700
Re: UB of memcpy(NULL, NULL, 0) Ike Naar <ike@iceland.freeshell.org> - 2016-10-24 06:11 +0000
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-24 00:58 -0700
Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-23 14:07 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 07:48 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 08:40 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 10:03 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 12:06 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 13:36 -0700
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-24 13:57 -0700
Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-24 14:16 -0700
Re: UB of memcpy(NULL, NULL, 0) supercat@casperkitty.com - 2016-10-24 17:23 -0700
Re: UB of memcpy(NULL, NULL, 0) Tim Rentsch <txr@alumni.caltech.edu> - 2016-10-25 07:57 -0700
Re: UB of memcpy(NULL, NULL, 0) James Kuyper <jameskuyper@verizon.net> - 2016-10-22 18:23 -0400
Re: UB of memcpy(NULL, NULL, 0) "James R. Kuyper" <jameskuyper@verizon.net> - 2016-10-23 10:44 -0400
Re: UB of memcpy(NULL, NULL, 0) Richard Heathfield <rjh@cpax.org.uk> - 2016-10-23 16:24 +0100
Re: Verbing Noob <root@127.0.0.1> - 2016-10-23 18:02 +0200
Re: UB of memcpy(NULL, NULL, 0) raltbos@xs4all.nl (Richard Bos) - 2016-10-23 13:26 +0000
Re: UB of memcpy(NULL, NULL, 0) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-10-23 07:40 -0700
Re: UB of memcpy(NULL, NULL, 0) asetofsymbols@gmail.com - 2016-10-21 23:56 -0700
Re: UB of memcpy(NULL, NULL, 0) Lőrinczy Zsigmond <nospam@for.me> - 2016-10-22 12:21 +0200
Re: UB of memcpy(NULL, NULL, 0) Keith Thompson <kst-u@mib.org> - 2016-10-22 16:33 -0700
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