Re: [Qemu-devel] [PATCH v1 13/17] arm: linux-user: don't set CPSR.E in BE32 mode

[Peter Maydell <peter.maydell@linaro.org>]

On 18 January 2016 at 07:12, Peter Crosthwaite
<crosthwaitepeter@gmail.com> wrote:
> Don't set CPSR.E for BE32 linux-user mode. As linux-user mode models
> BE32, using normal BE (and system mode will not), a special case is
> needed for user-mode where if sctlr.b is set, the CPU identifies as BE.
>
> Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
> ---
>
>  linux-user/main.c |  2 --
>  target-arm/cpu.h  | 12 +++++++++++-
>  2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index d481458..60375fb 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -4496,8 +4496,6 @@ int main(int argc, char **argv, char **envp)
>              env->uncached_cpsr |= CPSR_E;
>          } else {
>              env->cp15.sctlr_el[1] |= SCTLR_B;
> -            /* We model BE32 as regular BE, so set CPSR_E */
> -            env->uncached_cpsr |= CPSR_E;

...this is undoing what we just did in the previous patch and
which I reviewed as being the wrong thing there...

>          }
>  #endif
>      }
> diff --git a/target-arm/cpu.h b/target-arm/cpu.h
> index 3edd56b..96b1e99 100644
> --- a/target-arm/cpu.h
> +++ b/target-arm/cpu.h
> @@ -1812,7 +1812,17 @@ static bool arm_cpu_is_big_endian(CPUARMState *env)
>
>      /* In 32bit endianness is determined by looking at CPSR's E bit */
>      if (!is_a64(env)) {
> -        return (env->uncached_cpsr & CPSR_E) ? 1 : 0;
> +        return
> +#ifdef CONFIG_USER_ONLY
> +            /* In user mode, BE32 data accesses are just modelled as
> +             * regular BE access. In system mode, BE32 is modelled as
> +             * little endian, with the appropriate address translations on
> +             * non-word accesses. So sctlr.b only affects overall
> +             * endianness in user mode
> +             */
> +            arm_sctlr_b(env) ||
> +#endif
> +                ((env->uncached_cpsr & CPSR_E) ? 1 : 0);
>      }

This doesn't seem quite right -- for system emulation we currently
pick MO_BE or MO_LE based on the TB flag which is set according
to (arm_cpu_is_big_endian(env). So if we ignore SCTLR.B in
system mode then we'll still try to do LE accesses.

>      cur_el = arm_current_el(env);

thanks
-- PMM