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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/63303] Pointer subtraction is broken when using -fsanitize=undefined
Date: Fri, 19 Sep 2014 15:57:00 -0000 [thread overview]
Message-ID: <bug-63303-4-z6FV6VIFnS@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-63303-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63303
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to mikulas from comment #4)
> ... and another related problem (try this on 32-bit system):
>
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(void)
> {
> short *a = malloc(0x50000000 * sizeof(short));
> short *b = a + 0x50000000;
> printf("%ld\n", (long)(b - a));
> return 0;
> }
>
> Here, the return value should be positive (0x50000000), but it is negative.
> IMHO, according to the C standard, this is program correct and positive
> result should be returned.
This testcase is invalid, you really can't have an object bigger than half of
the address space in C/C++, pointer difference is signed ptrdiff_t and if you
have larger object, you can't subtract arbitrary char pointers in it anymore.
If you need more than 2GB in a single array, just use 64-bit system.
next prev parent reply other threads:[~2014-09-19 15:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-19 1:42 [Bug c/63303] New: " mikulas at artax dot karlin.mff.cuni.cz
2014-09-19 7:26 ` [Bug c/63303] " jakub at gcc dot gnu.org
2014-09-19 13:38 ` mikulas at artax dot karlin.mff.cuni.cz
2014-09-19 13:47 ` jakub at gcc dot gnu.org
2014-09-19 15:50 ` mikulas at artax dot karlin.mff.cuni.cz
2014-09-19 15:57 ` jakub at gcc dot gnu.org [this message]
2014-09-19 16:15 ` mikulas at artax dot karlin.mff.cuni.cz
2014-09-19 16:21 ` joseph at codesourcery dot com
2014-09-19 16:22 ` jakub at gcc dot gnu.org
2014-09-19 16:29 ` mikulas at artax dot karlin.mff.cuni.cz
2014-09-22 7:42 ` rguenth at gcc dot gnu.org
2014-09-22 14:31 ` mikulas at artax dot karlin.mff.cuni.cz
2015-10-19 11:03 ` rguenth at gcc dot gnu.org
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