kern/131597: [kernel] c++ exceptions very slow on FreeBSD
kostikbel at gmail.com
Fri Apr 23 17:16:13 UTC 2010
The following reply was made to PR kern/131597; it has been noted by GNATS.
From: Kostik Belousov <kostikbel at gmail.com>
To: John Baldwin <jhb at freebsd.org>
Cc: bug-followup at freebsd.org, guillaume at morinfr.org, kan at freebsd.org,
davidxu at freebsd.org
Subject: Re: kern/131597: [kernel] c++ exceptions very slow on FreeBSD 7.1/amd64
Date: Fri, 23 Apr 2010 16:47:40 +0300
Content-Type: text/plain; charset=us-ascii
On Fri, Apr 23, 2010 at 08:43:41AM -0400, John Baldwin wrote:
> On Friday 23 April 2010 8:25:01 am Kostik Belousov wrote:
> > On Thu, Apr 22, 2010 at 04:09:34PM -0400, John Baldwin wrote:
> > > I tracked the sigprocmask() system calls down to the operations to
> > > acquire a write lock in the runtime linker. The lock was added to fix
> > > an earlier bug with throwing exceptions in multithreaded C++ apps. The
> > > relevant commit that added the lock is this:
> > >
> > > http://svn.freebsd.org/viewvc/base?view=3Drevision&revision=3D1788=
> > >
> > > Are exceptions permitted during a signal handler? If not, then in
> > > theory we would not need to invoke sigprocmask() for this particular
> > > lock perhaps? I'm not sure how easy that would be to achieve given the
> > > hooks to allow the thread library to overload the locking routines.
> > > Also, this doesn't explain the lack of sigprocmask() calls under i386.
> > > FreeBSD/i386 should be using the same locking code and thus invoking
> > > sigprocmask() for each exception as well.
> > Throwing an exception during asyncronous signal execution rises undefin=
> > behaviour, AFAIK. sigprocmask() is there to support libc_r, and cannot
> > be removed as far as we need to provide FreeBSD 4.x compatibility.
> Hmmm. Why does libthr use sigprocmask() for its rtld locks then? Is tha=
> just a copy-paste from libc_r that can be removed now?
Hmmm^2. It seems it is there to prevent recursive entry into rtld from
signal handler, that may reference yet unresolved symbol, e.g. libc
syscall wrapper, from PLT. So my patch is wrong.
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