Date: Thu, 28 Jun 2018 12:09:49 -0700 From: Conrad Meyer <cem@freebsd.org> To: Justin Hibbits <jrh29@alumni.cwru.edu> Cc: dab@freebsd.org, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r335765 - head/sys/sys Message-ID: <CAG6CVpXzD-27t3g9HCbZ_=5Uyo4VPj706yx8cUiFMhq7NrKe9w@mail.gmail.com> In-Reply-To: <CAHSQbTD5BtcvcMeA%2BZeAUfkdsB6F%2BY9G182rnOHwb-E%2ByGxCUw@mail.gmail.com> References: <201806281701.w5SH15eP011261@repo.freebsd.org> <CAHSQbTD5BtcvcMeA%2BZeAUfkdsB6F%2BY9G182rnOHwb-E%2ByGxCUw@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
I think the right initializer is something like:
*(kevp_) = (struct kevent) {
...
.ext = {
[0] = 0,
[1] = 0,
...
},
};
(I.e., use a C99 array static initializer to initialize the array
member of struct kevent.)
Best,
Conrad
On Thu, Jun 28, 2018 at 11:45 AM, Justin Hibbits <jrh29@alumni.cwru.edu> wrote:
> Hi David,
>
> On Thu, Jun 28, 2018 at 12:01 PM David Bright <dab@freebsd.org> wrote:
>>
>> Author: dab
>> Date: Thu Jun 28 17:01:04 2018
>> New Revision: 335765
>> URL: https://svnweb.freebsd.org/changeset/base/335765
>>
>> Log:
>> Remove potential identifier conflict in the EV_SET macro.
>>
>> PR43905 pointed out a problem with the EV_SET macro if the passed
>> struct kevent pointer were specified with an expression with side
>> effects (e.g., "kevp++"). This was fixed in rS110241, but by using a
>> local block that defined an internal variable (named "kevp") to get
>> the pointer value once. This worked, but could cause issues if an
>> existing variable named "kevp" is in scope. To avoid that issue,
>> jilles@ pointed out that "C99 compound literals and designated
>> initializers allow doing this cleanly using a macro". This change
>> incorporates that suggestion, essentially verbatim from jilles@
>> comment on PR43905, except retaining the old definition for pre-C99 or
>> non-STDC (e.g., C++) compilers.
>>
>> PR: 43905
>> Submitted by: Jilles Tjoelker (jilles@)
>> Reported by: Lamont Granquist <lamont@scriptkiddie.org>
>> Reviewed by: jmg (no comments), jilles
>> MFC after: 1 week
>> Sponsored by: Dell EMC
>> Differential Revision: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=43905
>>
>> Modified:
>> head/sys/sys/event.h
>>
>> Modified: head/sys/sys/event.h
>> ==============================================================================
>> --- head/sys/sys/event.h Thu Jun 28 15:30:51 2018 (r335764)
>> +++ head/sys/sys/event.h Thu Jun 28 17:01:04 2018 (r335765)
>> @@ -49,7 +49,26 @@
>> #define EVFILT_EMPTY (-13) /* empty send socket buf */
>> #define EVFILT_SYSCOUNT 13
>>
>> +#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
>> #define EV_SET(kevp_, a, b, c, d, e, f) do { \
>> + *(kevp_) = (struct kevent){ \
>> + .ident = (a), \
>> + .filter = (b), \
>> + .flags = (c), \
>> + .fflags = (d), \
>> + .data = (e), \
>> + .udata = (f), \
>> + .ext[0] = 0, \
>> + .ext[1] = 0, \
>> + .ext[2] = 0, \
>> + .ext[3] = 0, \
>> + }; \
>> +} while(0)
>> +#else /* Pre-C99 or not STDC (e.g., C++) */
>> +/* The definition of the local variable kevp could possibly conflict
>> + * with a user-defined value passed in parameters a-f.
>> + */
>> +#define EV_SET(kevp_, a, b, c, d, e, f) do { \
>> struct kevent *kevp = (kevp_); \
>> (kevp)->ident = (a); \
>> (kevp)->filter = (b); \
>> @@ -62,6 +81,7 @@
>> (kevp)->ext[2] = 0; \
>> (kevp)->ext[3] = 0; \
>> } while(0)
>> +#endif
>>
>> struct kevent {
>> __uintptr_t ident; /* identifier for this event */
>>
>
> This breaks gcc builds, with the following errors:
>
> 18:02:13 /usr/src/bin/pwait/pwait.c: In function 'main':
> 18:02:13 /usr/src/bin/pwait/pwait.c:144: warning: initialized field overwritten
> 18:02:13 /usr/src/bin/pwait/pwait.c:144: warning: (near initialization
> for '(anonymous).ext')
> 18:02:13 /usr/src/bin/pwait/pwait.c:144: warning: initialized field overwritten
> 18:02:13 /usr/src/bin/pwait/pwait.c:144: warning: (near initialization
> for '(anonymous).ext')
> 18:02:13 /usr/src/bin/pwait/pwait.c:144: warning: initialized field overwritten
> 18:02:13 /usr/src/bin/pwait/pwait.c:144: warning: (near initialization
> for '(anonymous).ext')
> 18:02:13 /usr/src/bin/pwait/pwait.c:158: warning: initialized field overwritten
> 18:02:13 /usr/src/bin/pwait/pwait.c:158: warning: (near initialization
> for '(anonymous).ext')
> 18:02:13 /usr/src/bin/pwait/pwait.c:158: warning: initialized field overwritten
> 18:02:13 /usr/src/bin/pwait/pwait.c:158: warning: (near initialization
> for '(anonymous).ext')
> 18:02:13 /usr/src/bin/pwait/pwait.c:158: warning: initialized field overwritten
> 18:02:13 /usr/src/bin/pwait/pwait.c:158: warning: (near initialization
> for '(anonymous).ext')
>
> This can be seen in the tinderbox (https://ci.freebsd.org/tinderbox)
>
> I encountered this as a failure in building usr.sbin/camdd, which
> shows the same type of error.
>
> - Justin
>
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAG6CVpXzD-27t3g9HCbZ_=5Uyo4VPj706yx8cUiFMhq7NrKe9w>