Date: Tue, 24 Aug 2004 11:20:00 -0700 From: Sean McNeil <sean@mcneil.com> To: Harti Brandt <harti@freebsd.org> Cc: current@freebsd.org Subject: Re: bsdtar core dumps Message-ID: <1093371600.10464.23.camel@server.mcneil.com> In-Reply-To: <20040824200225.V517@beagle.kn.op.dlr.de> References: <1092777586.92327.9.camel@server.mcneil.com> <20040817213813.GE3827@gothmog.gr><4127841D.6050104@freebsd.org> <1093369220.10362.6.camel@server.mcneil.com> <20040824200225.V517@beagle.kn.op.dlr.de>
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On Tue, 2004-08-24 at 11:08, Harti Brandt wrote: > On Tue, 24 Aug 2004, Sean McNeil wrote: > [snip] > > Sorry to jump in. > > You cannot use a va_list twice. As soon as someone call va_arg() on the > ap all the aps in the calling functions get invalid. The only thing that > can and must be done is that the function that did the va_start() must > call va_end. > > If you need it twice you must make a copy as in the patch below. > But the function call va_copy must also call va_end() on that copy > (this seems missing in the patch). I took the lead from /usr/src/lib/libc/stdio/vfprintf.c It happens to do a va_copy(orgap,ap) but never does a va_end(orgap). Either vfprintf.c is incorrect or it is not necessary to call va_end(). One point I would like to make clear - you _can_ use a va_list twice on architectures that will pass the va_list argument by value (i.e. i386). This makes it easy to produce faulty code for those architectures that pass by reference and thus have a side-effect. Since most people here are developing and testing on x86 machines I would think this problem to have happened more often than it has. Cheers, Sean
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