Re: [Qemu-devel] [PATCH v2 1/2] monitor: Split mon_get_cpu fn to remove ENV_GET_CPU

[Peter Crosthwaite]

On Tue, Jun 16, 2015 at 8:09 AM, Markus Armbruster <address@hidden> wrote:
> Peter Crosthwaite <address@hidden> writes:
>
>> The monitor currently has one helper, mon_get_cpu() which will return
>> an env pointer. The target specific users of this API want an env, but
>> all the target agnostic users really just want the cpu pointer. These
>> users then need to use the target-specifically defined ENV_GET_CPU to
>> navigate back up to the CPU from the ENV. Split the API for the two
>> uses cases to remove all need for ENV_GET_CPU.
>>
>> Reviewed-by: Richard Henderson <address@hidden>
>> Reviewed-by: Andreas Färber <address@hidden>
>> Signed-off-by: Peter Crosthwaite <address@hidden>
>> ---
>> Changed since v1:
>> s/mon_get_env/mon_get_cpu_env (Andreas review)
>> Avoid C99 declaration (RH review)
>> ---
>>  monitor.c | 65 
>> ++++++++++++++++++++++++++++-----------------------------------
>>  1 file changed, 29 insertions(+), 36 deletions(-)
>>
> [...]
>> @@ -1208,16 +1203,14 @@ static void monitor_printc(Monitor *mon, int c)
>>  static void memory_dump(Monitor *mon, int count, int format, int wsize,
>>                          hwaddr addr, int is_physical)
>>  {
>> -    CPUArchState *env;
>>      int l, line_size, i, max_digits, len;
>>      uint8_t buf[16];
>>      uint64_t v;
>>
>>      if (format == 'i') {
>> -        int flags;
>> -        flags = 0;
>> -        env = mon_get_cpu();
>> +        int flags = 0;
>>  #ifdef TARGET_I386
>> +        CPUArchState *env = mon_get_cpu_env();
>>          if (wsize == 2) {
>>              flags = 1;
>>          } else if (wsize == 4) {
>> @@ -1238,10 +1231,11 @@ static void memory_dump(Monitor *mon, int count, int 
>> format, int wsize,
>>          }
>>  #endif
>>  #ifdef TARGET_PPC
>> +        CPUArchState *env = mon_get_cpu_env();
>>          flags = msr_le << 16;
>>          flags |= env->bfd_mach;
>>  #endif
>> -        monitor_disas(mon, env, addr, count, is_physical, flags);
>> +        monitor_disas(mon, mon_get_cpu_env(), addr, count, is_physical, 
>> flags);
>>          return;
>>      }
>>
>> @@ -1280,8 +1274,7 @@ static void memory_dump(Monitor *mon, int count, int 
>> format, int wsize,
>>          if (is_physical) {
>>              cpu_physical_memory_read(addr, buf, l);
>>          } else {
>> -            env = mon_get_cpu();
>> -            if (cpu_memory_rw_debug(ENV_GET_CPU(env), addr, buf, l, 0) < 0) 
>> {
>> +            if (cpu_memory_rw_debug(mon_get_cpu(), addr, buf, l, 0) < 0) {
>>                  monitor_printf(mon, " Cannot access memory\n");
>>                  break;
>>              }
>
> You call mon_get_cpu_env() and mon_get_cpu() multiple times in this
> function, and declare CPUArchState *env twice (which rang my shadowing
> alarm bell; fortunately the two are under mutually exclusive #ifdef).
> Why not simply do
>
>     CPUState *cpu = mon_get_cpu();

This we can do easily and the choice of the existing code is pure
personal preference. I generally prefer inline calls to trivial
getters for a low number of call sites as I think code is slightly
easier to read when you don't have to do a local variable lookup on
where all the function args are coming from.

>     CPUArchState *env = mon_get_cpu_env();
>

So the multiple decl of env is now needed to avoid an unused variable
werror for non-x86-non-PPC builds when considering the change in P2.
Not strictly needed until P2, but doing it this way straight up
slightly minimises churn. The ENV_GET_CPU removal and the change in P2
remove the only two unconditional uses of env forcing this variable to
go local to its #ifdef usages. It also has the advantage that only
those two arches use the env at all. Envlessness is a good thing for
common code so prefer to leave the multi-defs in target specific code
with a plan to get rid of them one by one with X86/PPC specific
patches that operate solely on their respective #ifdef sections.

FWIW, the follow up to this series adds the infrastructure needed for
getting rid of these #ifdef sections (once I muster the courage to
patch X86 and PPC):

https://lists.gnu.org/archive/html/qemu-devel/2015-05/msg04742.html

> right at the beginning and be done with it?
>
> Not a big deal, I'm willing to take this patch through my tree as is.
>

Let me know if you need respin for the first change. I can turn it
around quickly, i'd really like to get this one through as its
blocking a lot of the multi-arch work!

Regards,
Peter

> [...]
>