Date: Tue, 5 Dec 2000 08:58:17 -0800 (PST) From: John Polstra <jdp@polstra.com> To: stable@freebsd.org Cc: mreimer@vpop.net Subject: Re: Mysql segfaults; is the culprit libstdc++, pthread, regex ...? Message-ID: <200012051658.eB5GwHU25440@vashon.polstra.com> In-Reply-To: <3A2C40DD.3E0E5746@vpop.net> References: <3A2C40DD.3E0E5746@vpop.net>
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In article <3A2C40DD.3E0E5746@vpop.net>,
Matthew Reimer <mreimer@vpop.net> wrote:
> We've been having problems with mysql segfaulting. It seems to occur
> when it tries to return from a function, so maybe the stack is getting
> stomped.
Sergey Osokin recently reported a very similar problem
on a different threaded C++ program. See message ID
<20001124174554.A473@freebsd.org.ru> in the -hackers archives -- it
contains a small test case. I spent a few hours looking at it last
weekend, but I wasn't able to solve the problem. The failure occurs
in a function like this:
void
SS::run()
{
string s; // !!!
string s1; // !!!
sleep(1);
}
Upon returning from the function, the destructors for s1 and s get
called, in that order. The first one seems to corrupt the stack or
a register somehow, such that the code leading up to the call of the
second destructor dereferences a garbage pointer. In Sergey's case,
merely re-ordering two declarations in a different function makes the
problem appear or disappear:
void
SS::spawn()
{
#ifdef BAD
int rc;
Guard guard(m1); // !!!
#else
Guard guard(m1); // !!!
int rc;
#endif
According to Sergey, the problem arose in -stable some time around 12
November 2000. Sergey has been doing some further investigation to
narrow down the changes that caused the problem. I haven't had time
to digest his findings yet, and due to work pressures I may not find
time soon.
In any case, this appears to be a genuine bug that we (FreeBSD)
introduced.
John
--
John Polstra jdp@polstra.com
John D. Polstra & Co., Inc. Seattle, Washington USA
"Disappointment is a good sign of basic intelligence." -- Chögyam Trungpa
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