Re: [RFC] To fork or to vfork

[Daniel Jacobowitz <drow@false.org>]

On Tue, Nov 23, 2004 at 11:17:03PM +0100, Mark Kettenis wrote:
> It's now pretty clear to me why HP-UX 11.xx needs -Dvfork=fork.  In
> order to set up a child to be traced using the HP-UX ttrace(2) system
> call, it needs to do some handshaking.  It uses two pipes to do this.
> The child writes to one end to indicate that it's ready to be traced.
> When the parent is able to read from the other end it will set things
> up such that the child is properly traced.  It then indicates that the
> child may continue by writing on the other pipe.  However, since the
> parent is suspended while the child is in the vforked state, this
> doesn't work, and the debugger hangs.
> 
> Now I think we all agree that the -Dvfork=fork is pretty ugly.  Here's
> an alternate approach.  It's pretty likely that if PRE_TRACE_FUN is
> non-null things are complicated enough that it's unlikely that a vfork
> will work correctly.  I therefore propose the attached patch.
> 
> If there are no objections, I'll check this in in a few days.

No objections - this sounds like a great reason to use fork.

We're already stretching (read: way past) what is guaranteed to work
after vfork, and it's bitten us before, but the optimization is so
important on some targets...

-- 
Daniel Jacobowitz