Re: [RFC v7 12/22] cpu: Introduce TCGCpuOperations struct

[Claudio Fontana]

On 12/4/20 6:28 PM, Eduardo Habkost wrote:
> On Fri, Dec 04, 2020 at 06:10:49PM +0100, Philippe Mathieu-Daudé wrote:
>> On 11/30/20 3:35 AM, Claudio Fontana wrote:
>>> From: Eduardo Habkost <ehabkost@redhat.com>
>>>
>>> The TCG-specific CPU methods will be moved to a separate struct,
>>> to make it easier to move accel-specific code outside generic CPU
>>> code in the future.  Start by moving tcg_initialize().
>>
>> Good idea! One minor comment below.
>>
>>>
>>> The new CPUClass.tcg_opts field may eventually become a pointer,
>>> but keep it an embedded struct for now, to make code conversion
>>> easier.
>>>
>>> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
>>> ---
>>>  MAINTAINERS                     |  1 +
>>>  cpu.c                           |  2 +-
>>>  include/hw/core/cpu.h           |  9 ++++++++-
>>>  include/hw/core/tcg-cpu-ops.h   | 25 +++++++++++++++++++++++++
>>>  target/alpha/cpu.c              |  2 +-
>>>  target/arm/cpu.c                |  2 +-
>>>  target/avr/cpu.c                |  2 +-
>>>  target/cris/cpu.c               | 12 ++++++------
>>>  target/hppa/cpu.c               |  2 +-
>>>  target/i386/tcg-cpu.c           |  2 +-
>>>  target/lm32/cpu.c               |  2 +-
>>>  target/m68k/cpu.c               |  2 +-
>>>  target/microblaze/cpu.c         |  2 +-
>>>  target/mips/cpu.c               |  2 +-
>>>  target/moxie/cpu.c              |  2 +-
>>>  target/nios2/cpu.c              |  2 +-
>>>  target/openrisc/cpu.c           |  2 +-
>>>  target/ppc/translate_init.c.inc |  2 +-
>>>  target/riscv/cpu.c              |  2 +-
>>>  target/rx/cpu.c                 |  2 +-
>>>  target/s390x/cpu.c              |  2 +-
>>>  target/sh4/cpu.c                |  2 +-
>>>  target/sparc/cpu.c              |  2 +-
>>>  target/tilegx/cpu.c             |  2 +-
>>>  target/tricore/cpu.c            |  2 +-
>>>  target/unicore32/cpu.c          |  2 +-
>>>  target/xtensa/cpu.c             |  2 +-
>>>  27 files changed, 63 insertions(+), 30 deletions(-)
>>>  create mode 100644 include/hw/core/tcg-cpu-ops.h
>>>
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index f53f2678d8..d876f504a6 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -1535,6 +1535,7 @@ F: qapi/machine.json
>>>  F: qapi/machine-target.json
>>>  F: include/hw/boards.h
>>>  F: include/hw/core/cpu.h
>>> +F: include/hw/core/tcg-cpu-ops.h
>>>  F: include/hw/cpu/cluster.h
>>>  F: include/sysemu/numa.h
>>>  T: git https://github.com/ehabkost/qemu.git machine-next
>>> diff --git a/cpu.c b/cpu.c
>>> index 0be5dcb6f3..d02c2a17f1 100644
>>> --- a/cpu.c
>>> +++ b/cpu.c
>>> @@ -180,7 +180,7 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
>>>  
>>>      if (tcg_enabled() && !tcg_target_initialized) {
>>>          tcg_target_initialized = true;
>>> -        cc->tcg_initialize();
>>> +        cc->tcg_ops.initialize();
>>>      }
>>>      tlb_init(cpu);
>>>  
>>> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
>>> index 3d92c967ff..c93b08a0fb 100644
>>> --- a/include/hw/core/cpu.h
>>> +++ b/include/hw/core/cpu.h
>>> @@ -76,6 +76,10 @@ typedef struct CPUWatchpoint CPUWatchpoint;
>>>  
>>>  struct TranslationBlock;
>>>  
>>> +#ifdef CONFIG_TCG
>>> +#include "tcg-cpu-ops.h"
>>> +#endif /* CONFIG_TCG */
>>> +
>>>  /**
>>>   * CPUClass:
>>>   * @class_by_name: Callback to map -cpu command line model name to an
>>> @@ -221,12 +225,15 @@ struct CPUClass {
>>>  
>>>      void (*disas_set_info)(CPUState *cpu, disassemble_info *info);
>>>      vaddr (*adjust_watchpoint_address)(CPUState *cpu, vaddr addr, int len);
>>> -    void (*tcg_initialize)(void);
>>>  
>>>      const char *deprecation_note;
>>>      /* Keep non-pointer data at the end to minimize holes.  */
>>>      int gdb_num_core_regs;
>>>      bool gdb_stop_before_watchpoint;
>>> +
>>> +#ifdef CONFIG_TCG
>>> +    TcgCpuOperations tcg_ops;
>>> +#endif /* CONFIG_TCG */
>>>  };
> 
> I'm not a fan of #ifdefs in struct definitions (especially in
> generic code like hw/cpu), because there's risk the same header
> generate different struct layout when used by different .c files.
> I would prefer to gradually refactor the code so that tcg_ops is
> eventually removed from CPUClass.
> 
> This is not a dealbreaker, because both approaches are steps in
> the same direction.  But the #ifdef here makes review harder and
> has more risks of unwanted side effects.
> 
>>>  
>>>  /*
>>> diff --git a/include/hw/core/tcg-cpu-ops.h b/include/hw/core/tcg-cpu-ops.h
>>> new file mode 100644
>>> index 0000000000..4475ef0996
>>> --- /dev/null
>>> +++ b/include/hw/core/tcg-cpu-ops.h
>>> @@ -0,0 +1,25 @@
>>> +/*
>>> + * TCG-Specific operations that are not meaningful for hardware 
>>> accelerators
>>> + *
>>> + * Copyright 2020 SUSE LLC
>>> + *
>>> + * This work is licensed under the terms of the GNU GPL, version 2 or 
>>> later.
>>> + * See the COPYING file in the top-level directory.
>>> + */
>>> +
>>> +#ifndef TCG_CPU_OPS_H
>>> +#define TCG_CPU_OPS_H
>>> +
>>> +/**
>>> + * struct TcgCpuOperations: TCG operations specific to a CPU class
>>> + */
>>> +typedef struct TcgCpuOperations {
>>> +    /**
>>> +     * @initialize: Initalize TCG state
>>> +     *
>>> +     * Called when the first CPU is realized.
>>> +     */
>>> +    void (*initialize)(void);
>>> +} TcgCpuOperations;
>>> +
>>> +#endif /* TCG_CPU_OPS_H */
>> ...
>>
>>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>>> index 07492e9f9a..1fa9382a7c 100644
>>> --- a/target/arm/cpu.c
>>> +++ b/target/arm/cpu.c
>>> @@ -2261,7 +2261,7 @@ static void arm_cpu_class_init(ObjectClass *oc, void 
>>> *data)
>>>      cc->gdb_stop_before_watchpoint = true;
>>>      cc->disas_set_info = arm_disas_set_info;
>>>  #ifdef CONFIG_TCG
>>> -    cc->tcg_initialize = arm_translate_init;
>>> +    cc->tcg_ops.initialize = arm_translate_init;
>>
>> This one is correctly guarded by '#ifdef CONFIG_TCG'.
>>
>> For the other targets, can you either place it within
>> the '#ifdef CONFIG_TCG' block or if there is none, add
>> one please?
> 
> As a new #ifdef risks having additional unwanted side effects, I
> would prefer to do it in separate patch, just in case.
> 
> This also applies to the #ifdef Claudio added to hw/core/cpu.h
> above.  In case we really want to do it, I would do it in a
> separate patch.

Hi Eduardo,

yes, once things are settling we should dispose of as many #ifdefs are possible

Ciao,

Claudio

> 
>>
>> With that change:
>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> 
> Thanks!
>