* Defining _GNU_SOURCE hides the declaration of aligned_alloc
@ 2016-02-02 22:27 Ken Brown
2016-02-02 23:41 ` Ken Brown
2016-02-03 3:15 ` Yaakov Selkowitz
0 siblings, 2 replies; 3+ messages in thread
From: Ken Brown @ 2016-02-02 22:27 UTC (permalink / raw)
To: cygwin
The issue in the Subject line came up in connection with an emacs bug
report.
Here's a test case:
$ cat test.c
#define _GNU_SOURCE
#include <stdlib.h>
int
main ()
{
aligned_alloc (1, 1);
}
$ gcc test.c -Wimplicit-function-declaration
test.c: In function âmainâ:
test.c:7:3: warning: implicit declaration of function âaligned_allocâ
The cause is that the declaration of aligned_alloc in stdlib.h is
guarded by #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L; but
defining _GNU_SOURCE causes __ISO_C_VISIBLE to be defined as 1999.
Here's an excerpt from /usr/include/sys/cdefs.h showing how this happens:
/* Deal with _GNU_SOURCE, which implies everything and the kitchen sink */
#ifdef _GNU_SOURCE
[...]
#define _XOPEN_SOURCE 700
[...]
#endif
[...]
#if _XOPEN_SOURCE - 0 >= 700
[...]
#define _POSIX_C_SOURCE 200809
[...]
#endif
[...]
#if _POSIX_C_SOURCE >= 200809
[...]
#define __ISO_C_VISIBLE 1999
[...]
#endif /* _POSIX_C_SOURCE */
According to the discussion of the emacs bug I mentioned, Linux and
FreeBSD don't have this issue. Should Cygwin's headers be changed to
conform to those other platforms?
Ken
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Defining _GNU_SOURCE hides the declaration of aligned_alloc
2016-02-02 22:27 Defining _GNU_SOURCE hides the declaration of aligned_alloc Ken Brown
@ 2016-02-02 23:41 ` Ken Brown
2016-02-03 3:15 ` Yaakov Selkowitz
1 sibling, 0 replies; 3+ messages in thread
From: Ken Brown @ 2016-02-02 23:41 UTC (permalink / raw)
To: cygwin
On 2/2/2016 5:27 PM, Ken Brown wrote:
> The issue in the Subject line came up in connection with an emacs bug
> report.
>
> Here's a test case:
>
> $ cat test.c
> #define _GNU_SOURCE
> #include <stdlib.h>
>
> int
> main ()
> {
> aligned_alloc (1, 1);
> }
>
> $ gcc test.c -Wimplicit-function-declaration
> test.c: In function âmainâ:
> test.c:7:3: warning: implicit declaration of function âaligned_allocâ
>
> The cause is that the declaration of aligned_alloc in stdlib.h is
> guarded by #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L; but
> defining _GNU_SOURCE causes __ISO_C_VISIBLE to be defined as 1999.
> Here's an excerpt from /usr/include/sys/cdefs.h showing how this happens:
>
> /* Deal with _GNU_SOURCE, which implies everything and the kitchen sink */
> #ifdef _GNU_SOURCE
> [...]
> #define _XOPEN_SOURCE 700
> [...]
> #endif
> [...]
> #if _XOPEN_SOURCE - 0 >= 700
> [...]
> #define _POSIX_C_SOURCE 200809
> [...]
> #endif
> [...]
> #if _POSIX_C_SOURCE >= 200809
> [...]
> #define __ISO_C_VISIBLE 1999
> [...]
> #endif /* _POSIX_C_SOURCE */
>
> According to the discussion of the emacs bug I mentioned, Linux and
> FreeBSD don't have this issue. Should Cygwin's headers be changed to
> conform to those other platforms?
Paul Eggert says they should:
> Defining _GNU_SOURCE should make aligned_alloc visible regardless of whether -std=c99 is specified. This is because defining _GNU_SOURCE means, "Make GNU symbols visible even when compiling pedantically." This is OK, since the C standard says the behavior is undefined whenever the user defines a reserved symbol like _GNU_SOURCE.
Ken
--
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Defining _GNU_SOURCE hides the declaration of aligned_alloc
2016-02-02 22:27 Defining _GNU_SOURCE hides the declaration of aligned_alloc Ken Brown
2016-02-02 23:41 ` Ken Brown
@ 2016-02-03 3:15 ` Yaakov Selkowitz
1 sibling, 0 replies; 3+ messages in thread
From: Yaakov Selkowitz @ 2016-02-03 3:15 UTC (permalink / raw)
To: cygwin
On 2016-02-02 16:27, Ken Brown wrote:
> The issue in the Subject line came up in connection with an emacs bug
> report.
>
> Here's a test case:
[snip]
> $ gcc test.c -Wimplicit-function-declaration
> test.c: In function âmainâ:
> test.c:7:3: warning: implicit declaration of function âaligned_allocâ
>
> The cause is that the declaration of aligned_alloc in stdlib.h is
> guarded by #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L; but
> defining _GNU_SOURCE causes __ISO_C_VISIBLE to be defined as 1999.
> Here's an excerpt from /usr/include/sys/cdefs.h showing how this happens:
[snip]
> According to the discussion of the emacs bug I mentioned, Linux and
> FreeBSD don't have this issue. Should Cygwin's headers be changed to
> conform to those other platforms?
Yes, it should. I have added this to my queue of such fixes, which I
hope to post soon.
--
Yaakov
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
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^ permalink raw reply [flat|nested] 3+ messages in thread
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