Date: Sun, 21 Jun 2015 16:09:48 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Pedro Giffuni <pfg@freebsd.org> Cc: Bruce Evans <brde@optusnet.com.au>, Dimitry Andric <dim@freebsd.org>, David Chisnall <theraven@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r268137 - head/sys/sys Message-ID: <20150621154332.U976@besplex.bde.org> In-Reply-To: <55861046.4050501@FreeBSD.org> References: <201407020845.s628jRG5031824@svn.freebsd.org> <5BE3492F-86A0-4CE3-A27C-8DB5EB662C64@FreeBSD.org> <55842F16.5040608@FreeBSD.org> <D58BE060-870A-4D5E-AE46-D915D9CD6A0C@FreeBSD.org> <20150620023835.N2562@besplex.bde.org> <55861046.4050501@FreeBSD.org>
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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:
>>=20
>>> On 19 Jun 2015, at 17:02, Pedro Giffuni <pfg@freebsd.org> wrote:
>>>>=20
>>>>> On 19/06/2015 05:16 a.m., David Chisnall wrote:
>>>>>> I only just caught this (having seen the fallout from NetBSD doing t=
he=20
>>>>>> same thing in a shipping release and the pain that it=E2=80=99s caus=
ed):
>>>>>> __weak is a reserved keyword in Objective-C, please pick another nam=
e=20
>>>>>> for this. This in cdefs.h makes it impossible to include any FreeBS=
D=20
>>>>>> standard headers in Objective-C programs (of which we have a couple =
of=20
>>>>>> hundred in ports) if they use any of the modern Objective-C language=
=20
>>>>>> modes.
>>> ...
>>>> Closely related to this, we are redefining _Noreturn, which is a reser=
ved=20
>>>> keyword in C11.
>>>=20
>>> No, sys/cdefs.h has:
>>>=20
>>> 254 /*
>>> 255 * Keywords added in C11.
>>> 256 */
>>> 257
>>> 258 #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L ||=
=20
>>> defined(lint)
>>> [...]
>>> 284 #if defined(__cplusplus) && __cplusplus >=3D 201103L
>>> 285 #define _Noreturn [[noreturn]]
>>> 286 #else
>>> 287 #define _Noreturn __dead2
>>> 288 #endif
>>> [...]
>>> 320 #endif /* __STDC_VERSION__ || __STDC_VERSION__ < 201112L */
>>>=20
>>> So the whole block redefining all the _Xxx identifiers is skipped for
>>> C11 and higher.
>>=20
>> I probably pointed this out incorrectly to Pedro.
>>=20
>> 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.
>>=20
> 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:
>>=20
>> __dead void
>> foo(void) __dead2;
>>=20
>
> 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. I checked this:
pts/23:bde@freefall:~/s> cc -O -S a.c -std=3Dc11
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 stor=
age c
lass
Here is the broken part of x86/_types.h:
%%%
#ifdef __GNUCLIKE_BUILTIN_VARARGS
typedef __builtin_va_list=09__va_list;=09/* internally known to gcc */
#elif defined(lint)
typedef char *=09=09=09__va_list;=09/* 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=09=09__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 availab=
le.
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.
Bruce
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To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r284670 - head/sys/dev/xen/blkfront
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Author: cperciva
Date: Sun Jun 21 06:52:03 2015
New Revision: 284670
URL: https://svnweb.freebsd.org/changeset/base/284670
Log:
Garbage collect comments and a macro which related to the pre-r284296
support for a "segment block" extension in FreeBSD's Xen blkfront/blkback
drivers.
This commit should not result in any functional changes.
Modified:
head/sys/dev/xen/blkfront/block.h
Modified: head/sys/dev/xen/blkfront/block.h
==============================================================================
--- head/sys/dev/xen/blkfront/block.h Sun Jun 21 06:49:44 2015 (r284669)
+++ head/sys/dev/xen/blkfront/block.h Sun Jun 21 06:52:03 2015 (r284670)
@@ -68,9 +68,8 @@
#define XBD_MAX_RING_PAGES 32
/**
- * The maximum number of outstanding requests blocks (request headers plus
- * additional segment blocks) we will allow in a negotiated block-front/back
- * communication channel.
+ * The maximum number of outstanding requests we will allow in a negotiated
+ * block-front/back communication channel.
*/
#define XBD_MAX_REQUESTS \
__CONST_RING_SIZE(blkif, PAGE_SIZE * XBD_MAX_RING_PAGES)
@@ -82,15 +81,6 @@
#define XBD_MAX_REQUEST_SIZE \
MIN(MAXPHYS, XBD_SEGS_TO_SIZE(BLKIF_MAX_SEGMENTS_PER_REQUEST))
-/**
- * The maximum number of segments (within a request header and accompanying
- * segment blocks) per request we will allow in a negotiated block-front/back
- * communication channel.
- */
-#define XBD_MAX_SEGMENTS_PER_REQUEST \
- (MIN(BLKIF_MAX_SEGMENTS_PER_REQUEST, \
- XBD_SIZE_TO_SEGS(XBD_MAX_REQUEST_SIZE)))
-
typedef enum {
XBDCF_Q_MASK = 0xFF,
/* This command has contributed to xbd_qfrozen_cnt. */
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