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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Wed, 31 May 2017 19:16:05 +0100
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Subject: Re: [Qemu-devel] [PATCH v1 2/2] gdbstub: don't fail on vCont; C04:0;
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To: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Cc: Greg Kurz <groug@kaod.org>, pbonzini@redhat.com, doug16k@gmail.com, qemu-devel@nongnu.org


Claudio Imbrenda <imbrenda@linux.vnet.ibm.com> writes:

> On Wed, 31 May 2017 19:06:29 +0200
> Greg Kurz <groug@kaod.org> wrote:
>
>> On Wed, 31 May 2017 18:51:06 +0200
>> Claudio Imbrenda <imbrenda@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.

OK I'll include a fix in the next iteration.

--
Alex Bennée