Re: [Qemu-devel] [PATCH 05/20] target/arm: Fix arm_cpu_data_is_big_endian for aa64 user-only

[Richard Henderson <richard.henderson@linaro.org>]

On 08/17/2018 09:02 AM, Peter Maydell wrote:
> On 9 August 2018 at 05:21, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>> Unlike aa32, endianness cannot be adjusted by userland in aa64.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>  target/arm/cpu.h | 27 +++++++++++++++++----------
>>  1 file changed, 17 insertions(+), 10 deletions(-)
>>
>> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
>> index 9526ed27cb..2d6d7d03aa 100644
>> --- a/target/arm/cpu.h
>> +++ b/target/arm/cpu.h
>> @@ -2709,8 +2709,6 @@ static inline bool arm_sctlr_b(CPUARMState *env)
>>  /* Return true if the processor is in big-endian mode. */
>>  static inline bool arm_cpu_data_is_big_endian(CPUARMState *env)
>>  {
>> -    int cur_el;
>> -
>>      /* In 32bit endianness is determined by looking at CPSR's E bit */
>>      if (!is_a64(env)) {
>>          return
>> @@ -2729,15 +2727,24 @@ static inline bool arm_cpu_data_is_big_endian(CPUARMState *env)
>>              arm_sctlr_b(env) ||
>>  #endif
>>                  ((env->uncached_cpsr & CPSR_E) ? 1 : 0);
>> +    } else {
>> +#ifdef CONFIG_USER_ONLY
>> +        /* AArch64 does not have a SETEND instruction; endianness
>> +         * for usermode is fixed at compile-time.
>> +         */
>> +# ifdef TARGET_WORDS_BIGENDIAN
>> +        return true;
>> +# else
>> +        return false;
>> +# endif
>> +#else
>> +        int cur_el = arm_current_el(env);
>> +        if (cur_el == 0) {
>> +            return (env->cp15.sctlr_el[1] & SCTLR_E0E) != 0;
>> +        }
>> +        return (env->cp15.sctlr_el[cur_el] & SCTLR_EE) != 0;
>> +#endif
>>      }
>> -
>> -    cur_el = arm_current_el(env);
>> -
>> -    if (cur_el == 0) {
>> -        return (env->cp15.sctlr_el[1] & SCTLR_E0E) != 0;
>> -    }
>> -
>> -    return (env->cp15.sctlr_el[cur_el] & SCTLR_EE) != 0;
>>  }
>>
> 
> When does this make a difference? For user-mode, we've already
> dealt with the "aa32" case, so the code here is aa64-only.
> In linux-user/aarch64/cpu_loop.c we set sctlr_el[1]'s E0E bit
> if TARGET_WORDS_BIGENDIAN is defined, and cur_el is definitely
> zero, so we should already be returning true from this function
> if TARGET_WORDS_BIGENDIAN and false otherwise.

I should have re-ordered this after the other following
simplifications to see if it still matters.  But I was
after a code-size reduction.


r~