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Re: all class init functions for all types in QEMU are called in select_
From: |
Claudio Fontana |
Subject: |
Re: all class init functions for all types in QEMU are called in select_machine(). Expected? |
Date: |
Fri, 12 Mar 2021 10:58:10 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 |
On 3/12/21 10:45 AM, Philippe Mathieu-Daudé wrote:
> On 3/12/21 10:31 AM, Claudio Fontana wrote:
>> Hello Paolo and all,
>>
>> while debugging a class init ordering issue, I noticed that
>>
>> _all_ class init functions for all types registered in the QEMU QOM are
>> called in select_machine().
>> Expected?
>>
>> In particular it happens here:
>>
>> static MachineClass *select_machine(void)
>> {
>> GSList *machines = object_class_get_list(TYPE_MACHINE, false);
>>
>>
>> object_class_get_list() ->
>> object_class_foreach() ->
>> g_hash_table_foreach() ->
>> object_class_foreach_tramp ->
>> type_initialize(type);
>>
>>
>> Is this really desired? It looks suspect to me.
>>
>> (gdb) bt
>> #0 0x0000555555db613f in arm_v7m_class_init (oc=0x555556dca320,
>> data=0x555556a926e0 <arm_tcg_cpus+288>)
>> at ../target/arm/tcg/tcg-cpu-models.c:849
>> #1 0x0000555555f1deba in type_initialize (ti=0x555556d5b2f0) at
>> ../qom/object.c:364
>> #2 0x0000555555f1f62a in object_class_foreach_tramp (key=0x555556d5b470,
>> value=0x555556d5b2f0, opaque=0x7fffffffda20)
>> at ../qom/object.c:1069
>> #3 0x00007ffff6562000 in g_hash_table_foreach () at
>> /usr/lib64/libglib-2.0.so.0
>> #4 0x0000555555f1f709 in object_class_foreach (fn=
>> 0x555555f1f866 <object_class_get_list_tramp>,
>> implements_type=0x555556381b09 "machine", include_abstract=false,
>> opaque=0x7fffffffda70)
>> at ../qom/object.c:1091
>> #5 0x0000555555f1f8e4 in object_class_get_list
>> (implements_type=0x555556381b09 "machine", include_abstract=false) at
>> ../qom/object.c:1148
>> #6 0x0000555555debe94 in select_machine () at ../softmmu/vl.c:1607
>>
>>
>> If not here, where should be the right place, for example, for CPU class
>> inits to be called?
>>
>> At the very least I would put a comment there around the beginning of
>> select_machine() saying:
>>
>> /* all types, all classes in QOM are initialized here, as a result of the
>> object_class_get_list call */
>>
>> Wdyt?
>
> Are you trying to register types conditionally?
>
Not really, but I have been using the accel class init function on x86 to
register the TCG OPS,
and this instead requires a bit more thought for ARM,
because we currently register for the ARM M Profile the TCG Ops at
arm_v7m_class_init time,
which is called already at select_machine() time,
so when we select the accelerator, and we call the tcg_cpu_class_init, we run
the risk of overriding the existing tcg_ops,
with the current result that we have to do:
static void tcg_cpu_class_init(CPUClass *cc)
{
/*
* do not overwrite the TCG ops, if already set by the
* arm cpu class (this is the case for the M profile CPUs).
*
* Otherwise, provide the default ARM TCG behavior here.
*/
if (!cc->tcg_ops) {
cc->tcg_ops = &arm_tcg_ops;
}
}
It's a fine result for me, but we do have an "if" inside a class_init.
Ideas? Looks horrible?
THanks,
Claudio
- all class init functions for all types in QEMU are called in select_machine(). Expected?, Claudio Fontana, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Philippe Mathieu-Daudé, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?,
Claudio Fontana <=
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Paolo Bonzini, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Claudio Fontana, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Paolo Bonzini, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Claudio Fontana, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Paolo Bonzini, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Claudio Fontana, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Claudio Fontana, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Paolo Bonzini, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Claudio Fontana, 2021/03/12
- Re: all class init functions for all types in QEMU are called in select_machine(). Expected?, Paolo Bonzini, 2021/03/12