On 06/21/15 01:09, Bruce Evans wrote:
On Sat, 20 Jun 2015, Pedro Giffuni wrote:
On 06/19/15 12:23, Bruce Evans wrote:
On Fri, 19 Jun 2015, Dimitry Andric wrote:
On 19 Jun 2015, at 17:02, Pedro Giffuni <p...@freebsd.org> wrote:
On 19/06/2015 05:16 a.m., David Chisnall wrote:
I only just caught this (having seen the fallout from NetBSD
doing the same thing in a shipping release and the pain that
it’s caused):
__weak is a reserved keyword in Objective-C, please pick another
name for this. This in cdefs.h makes it impossible to include
any FreeBSD standard headers in Objective-C programs (of which
we have a couple of hundred in ports) if they use any of the
modern Objective-C language modes.
...
Closely related to this, we are redefining _Noreturn, which is a
reserved keyword in C11.
No, sys/cdefs.h has:
254 /*
255 * Keywords added in C11.
256 */
257
258 #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L
|| defined(lint)
[...]
284 #if defined(__cplusplus) && __cplusplus >= 201103L
285 #define _Noreturn [[noreturn]]
286 #else
287 #define _Noreturn __dead2
288 #endif
[...]
320 #endif /* __STDC_VERSION__ || __STDC_VERSION__ < 201112L */
So the whole block redefining all the _Xxx identifiers is skipped for
C11 and higher.
I probably pointed this out incorrectly to Pedro.
All uses of _Noreturn are still broken, and also ugly. __dead2 is the
gcc-2 compatible version of the gcc-1 compatible macro __dead. It is
syntactically different from __dead and _Noreturn. It must be placed
after the function parameter list instead of in the function type
declarator because old versions of gcc only accept attributes there.
__dead and presumably _Noreturn must be placed in the function type
declarator. This is incompatible, and also uglier.
I was thinking that _Noreturn can be fixed for older compilers
less disruptively.
I haven't tested the attached patch the idea is to resurrect
__dead and use it for _Noreturn.
Correct version with ugly declarations:
__dead void
foo(void) __dead2;
With the patch we would use:
__Noreturn void
foo(void) _dead2;
Which is still ugly but C11-ish.
That asks for the same problems as defining __weak.
Why not just don't use _Noreturn? It is an unimprovement on the gcc
attribute. The attribute works at the beginning or end, while Noreturn
only works at the end.
As I see it, newer (C11) software is likely to use _Noreturn in their
headers
I checked this:
pts/23:bde@freefall:~/s> cc -O -S a.c -std=c11
a.c:3:26: error: '_Noreturn' keyword must precede function declarator
_Noreturn void bar(void) _Noreturn;
^
I also checked if __dead2 works at the beginning in gcc-2.95.4. It
does, but other headers are broken, so the support for gcc-2.95.4 in
sys/cdefs.h is almost useless:
pts/23:bde@freefall:~/s> gcc295 -O -S a.c
In file included from /usr/include/machine/_types.h:6,
from /usr/include/sys/_types.h:33,
from /usr/include/x86/endian.h:37,
from /usr/include/machine/endian.h:6,
from /usr/include/sys/types.h:44,
from a.c:1:
/usr/include/x86/_types.h:161: syntax error before `__gnuc_va_list'
/usr/include/x86/_types.h:161: warning: data definition has no type or
storage c
lass
Here is the broken part of x86/_types.h:
%%%
#ifdef __GNUCLIKE_BUILTIN_VARARGS
typedef __builtin_va_list __va_list; /* internally known to gcc */
#elif defined(lint)
typedef char * __va_list; /* pretend */
#endif
#if defined(__GNUC_VA_LIST_COMPATIBILITY) && !defined(__GNUC_VA_LIST) \
&& !defined(__NO_GNUC_VA_LIST)
#define __GNUC_VA_LIST
meta: next is line 161:
typedef __va_list __gnuc_va_list; /* compatibility w/GNU headers*/
#endif
%%%
Despite (rather, because of) mounds of ifdefs to support old gcc, it
doesn't
actually work.
<stdarg.h> is honestly broken. It knows that it depends on the gcc
feature
__GNUCLIKE_BUILTIN_STDARG, and aborts with an #error when it is not
available.
All of the _GNUCLIKE_BUILTIN_* macros for variadic args are controlled by
sys/cdefs.h. They are defined when the compiler is either gcc newer than
gcc-2.95 or is icc.
You have a point there: I tried to get the core team to at least deprecate
gcc <= 2.8.1 and they didn't reach an agreement. :(
I still think we could have older gcc work fine with _Noreturn and
that would be a step forward.
Pedro.
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