Re: [PATCH] linux-user: Don't assume 0 is not a valid host timer_t value

[Peter Maydell]

On Mon, 25 Jul 2022 at 12:13, Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> On Mon, Jul 25, 2022 at 12:00:35PM +0100, Peter Maydell wrote:
> > For handling guest POSIX timers, we currently use an array
> > g_posix_timers[], whose entries are a host timer_t value, or 0 for
> > "this slot is unused".  When the guest calls the timer_create syscall
> > we look through the array for a slot containing 0, and use that for
> > the new timer.
> >
> > This scheme assumes that host timer_t values can never be zero.  This
> > is unfortunately not a valid assumption -- for some host libc
> > versions, timer_t values are simply indexes starting at 0.  When
> > using this kind of host libc, the effect is that the first and second
> > timers end up sharing a slot, and so when the guest tries to operate
> > on the first timer it changes the second timer instead.
>
> For sake of historical record, could you mention here which specific
> libc impl / version highlights the problem.

How about:

"This can happen if you are using glibc's backwards-compatible
'timer_t is an integer' compat code for some reason. This happens
when a glibc newer than 2.3.3 is used for a program that was
linked to work with glibc 2.2 to 2.3.3."

Laurent, I'm going to assume you don't need a v2 sending just
for a commit message tweak, unless you'd like me to do that.

thanks
-- PMM