Subject: Re: COMPAT_LINUX vsyscall
To: Jonathan Stone <>
From: David Laight <>
List: tech-kern
Date: 05/01/2005 23:16:25
On Sun, May 01, 2005 at 02:50:06PM -0700, Jonathan Stone wrote:
> >
> >Why would you want to map a page of code into userspace?
> So the kernel has somewhere safe to put useful kernel-maintained
> information into the page, where userspace (libc) code can access that
> information, without paying the cost of crossing protection domains
> (syscall overhead or other means to trap into the kernel).
> For gettimeofday(), put base time-of-day, cycle-count, and a
> context-switch counter in the page, and you can compute gettimeofday()
> in userspace.  (use the csw counter to restart if a context-switch
> happens in the userspace code; c.f. LBL (Van Jacobsen? Craig Leres?)
> gettimeofday() for sun4c. Add frills as necessary for SMP).

That is mapping data, not code.....


David Laight: