Re: [PATCH] linux-user/arm: Reset CPSR_E when entering a signal handler

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

On Thu, 7 May 2020 at 21:25, Amanieu d'Antras <amanieu@gmail.com> wrote:
>
> This fixes signal handlers running with the wrong endianness if the
> interrupted code used SETEND to dynamically switch endianness.
>
> Signed-off-by: Amanieu d'Antras <amanieu@gmail.com>
> ---
>  linux-user/arm/signal.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/arm/signal.c b/linux-user/arm/signal.c
> index d96fc27ce1..8aca5f61b7 100644
> --- a/linux-user/arm/signal.c
> +++ b/linux-user/arm/signal.c
> @@ -244,6 +244,12 @@ setup_return(CPUARMState *env, struct target_sigaction *ka,
>      } else {
>          cpsr &= ~CPSR_T;
>      }
> +    cpsr &= ~CPSR_E;
> +#ifdef TARGET_WORDS_BIGENDIAN
> +    if (env->cp15.sctlr_el[1] & SCTLR_E0E) {
> +        cpsr |= CPSR_E;
> +    }
> +#endif
>
>      if (ka->sa_flags & TARGET_SA_RESTORER) {
>          if (is_fdpic) {
> @@ -287,7 +293,8 @@ setup_return(CPUARMState *env, struct target_sigaction *ka,
>      env->regs[13] = frame_addr;
>      env->regs[14] = retcode;
>      env->regs[15] = handler & (thumb ? ~1 : ~3);
> -    cpsr_write(env, cpsr, CPSR_IT | CPSR_T, CPSRWriteByInstr);
> +    cpsr_write(env, cpsr, CPSR_IT | CPSR_T | CPSR_E, CPSRWriteByInstr);
> +    arm_rebuild_hflags(env);

I was just looking at the signal code's handling of CPSR for a different
reason, and I noticed that at the moment we don't allow CPSR.E to be
updated from the signal frame when the signal handler returns
(because CPSR_USER doesn't contain CPSR_E and that's what we
use in restore_sigcontext() to define what bits from the frame we
allow updating). Don't you find that when the interrupted code
returns from the signal handler that it ends up running with the
wrong endianness (ie the endianness the handler used) ?

I'm going to fix this by putting CPSR_E in CPSR_USER, anyway.

thanks
-- PMM