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Re: [libvirt] [PATCH] maint: update to latest gnulib



On Thu, Jun 15, 2017 at 05:39:00PM +0200, Martin Kletzander wrote:
> On Wed, Jun 14, 2017 at 03:35:39PM +0100, Daniel P. Berrange wrote:
> > On Wed, Jun 14, 2017 at 04:30:49PM +0200, Martin Kletzander wrote:
> > > On Wed, Jun 14, 2017 at 02:32:41PM +0100, Daniel P. Berrange wrote:
> > > > On Wed, Jun 14, 2017 at 03:27:25PM +0200, Martin Kletzander wrote:
> > > > > On Wed, Jun 14, 2017 at 11:20:44AM +0100, Daniel P. Berrange wrote:
> > > > > > This fixes an incompatibility with glibc 2.25.90
> > > > > >
> > > > > > Signed-off-by: Daniel P. Berrange <berrange redhat com>
> > > > > > ---
> > > > > >
> > > > > > Pushed as a broken build fix to get CI back online
> > > > > >
> > > > >
> > > > > After this update the build fails for me with gcc-7.1.0 with the
> > > > > following error:
> > > > >
> > > > > In file included from util/virobject.c:28:0:
> > > > > util/virobject.c: In function 'virClassNew':
> > > > > util/viratomic.h:176:46: error: this condition has identical branches [-Werror=duplicated-branches]
> > > > >             (void)(0 ? *(atomic) ^ *(atomic) : 0);                      \
> > > > >                                              ^
> > > > > util/virobject.c:144:20: note: in expansion of macro 'virAtomicIntInc'
> > > > >     klass->magic = virAtomicIntInc(&magicCounter);
> > > > >                    ^~~~~~~~~~~~~~~
> > > > >
> > > > > Does that mean that gcc does optimize our prefetch trick away
> > > > > (considering I understood what that line is trying to do)?  Or should we
> > > > > just turn the warning off for that header file?
> > > >
> > > > Yep, "-Wduplicated-branches" appears to be a new warning flag in gcc 7.1
> > > > which gnulib turns on. There's a similar hit with mingw
> > > >
> > > > ../../src/util/vircommand.c: In function 'virCommandWait':
> > > > ../../src/util/vircommand.c:2562:51: error: this condition has identical branches [-Werror=duplicated-branches]
> > > >             *exitstatus = cmd->rawStatus ? status : WEXITSTATUS(status);
> > > >                                                   ^
> > > > cc1: all warnings being treated as errors
> > > >
> > > >
> > > > because WEXITSTATUS(x) expands to 'x' on Win32.
> > > >
> > > > We could use a pragma to turn off selectively, but I'm more
> > > > inclined to just disable this new warning flag.
> > > >
> > > 
> > > Well, I'm not sure how that affects the line where we actually use it
> > > (with the atomic variables) or whether that line is not needed anymore
> > > (if that was a fix for older compilers or something similar).  But I
> > > can send a patch for removing that warning.  How about the other
> > > warning we get when we turn off the first one?  I just found out.  I
> > > think that could be turned off as well, either for some particular
> > > places or for the whole build:
> > > 
> > > util/virtime.c: In function 'virTimeStringThenRaw':
> > > util/virtime.c:215:9: error: '%02d' directive output may be truncated writing between 2 and 11 bytes into a region of size between 5 and 21 [-Werror=format-truncation=]
> > >     if (snprintf(buf, VIR_TIME_STRING_BUFLEN,
> > >         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >                  "%4d-%02d-%02d %02d:%02d:%02d.%03d+0000",
> > >                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >                  fields.tm_year, fields.tm_mon, fields.tm_mday,
> > >                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >                  fields.tm_hour, fields.tm_min, fields.tm_sec,
> > >                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >                  (int) (when % 1000)) >= VIR_TIME_STRING_BUFLEN) {
> > >                  ~~~~~~~~~~~~~~~~~~~~
> > > util/virtime.c:215:9: note: using the range [-2147483648, 2147483647] for directive argument
> > > In file included from /usr/include/stdio.h:936:0,
> > >                 from ../gnulib/lib/stdio.h:43,
> > >                 from util/virtime.c:36:
> > > /usr/include/bits/stdio2.h:64:10: note: '__builtin___snprintf_chk' output between 29 and 89 bytes into a destination of size 29
> > >   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
> > >          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >        __bos (__s), __fmt, __va_arg_pack ());
> > >        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > I think we might just want to switch to asprintf here instead of trying to
> > optimize into a fixed stack allocated buffer.
> > 
> 
> I wanted to do that and started rewriting it, but I found out we use
> static buffers in lot of places and lot of them then use snprintf or
> similar.  In some cases it doesn't even make much of a sense, e.g.:
> 
>  snprintf(buf, 3, "%d", var)
> 
> even this can fail.  I get the reason for the warning, but I don't
> really agree that it's something that is necessary to avoid, so I'm
> inclining to ignoring that warning as well.

In that kind of scenario we should be using  INT_BUFSIZE_BOUND(var)
to declare the 'buf' array, rather than hardcoding a fixed size
based on assumptions about likely max value of var.

Regards,
Daniel
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