On Wed, 31 May 2017 19:06:29 +0200
Greg Kurz <gr...@kaod.org> wrote:
> On Wed, 31 May 2017 18:51:06 +0200
> Claudio Imbrenda <imbre...@linux.vnet.ibm.com> wrote:
> [...]
> > > >
> > > > This is strange. cpu_index() is defined as:
> > > >
> > > > static inline int cpu_index(CPUState *cpu)
> > > > {
> > > > #if defined(CONFIG_USER_ONLY)
> > > > return cpu->host_tid;
> > > > #else
> > > > return cpu->cpu_index + 1;
> > > > #endif
> > > > }
> > > >
> > > > therefore it shouldn't return 0 under any circumstance,
> > > > and
> > >
> > > I think it is 0 for first_cpu in user mode.
> >
> > in linux-user/syscall.c:
> >
> > info->tid = gettid();
> > cpu->host_tid = info->tid;
> >
> > kernel thread-ids are system-wide unique and can't be 0
> >
>
> This is correct but these lines are in clone_func(). This gets called
> for all threads but the "main" thread which I believe to be
> associated to first_cpu.
then IMHO that is a bug and it needs to be corrected. the host_tid
should be, well, the host tid, and not 0, which is never a valid
tid for Linux.
the current behaviour is simply the easiest for the "any CPU" case.
Picking the last CPU or a random one would still be correct, and in
that case there would be no way to explicitly address the first CPU.
