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

[Eduardo Habkost <ehabkost@redhat.com>]

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.

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

Thanks!

-- 
Eduardo