Re: [Qemu-devel] [PATCH 11/21] target-mips: Status.UX/SX/KX enable 32-bit address wrapping

[Aurelien Jarno]

On Fri, May 30, 2014 at 03:47:49PM +0100, Leon Alrae wrote:
> In R6 the special behaviour for data references is also specified for Kernel
> and Supervisor mode. Therefore MIPS_HFLAG_UX is replaced by generic 
> MIPS_HFLAG_X
> indicating whether 64-bit mode is enabled in current operating mode.

I haven't found any indication of that in the MIPS64R6 manual (MD00091
version 6.00). Section 4.10 still only mentions the user mode.

Did I miss something?

> Signed-off-by: Leon Alrae <address@hidden>
> ---
>  target-mips/cpu.h       |   14 ++++++++++----
>  target-mips/translate.c |   20 +++++++++++++++-----
>  2 files changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/target-mips/cpu.h b/target-mips/cpu.h
> index 6c2014e..3dbc219 100644
> --- a/target-mips/cpu.h
> +++ b/target-mips/cpu.h
> @@ -447,7 +447,7 @@ struct CPUMIPSState {
>         and RSQRT.D.  */
>  #define MIPS_HFLAG_COP1X  0x00080 /* COP1X instructions enabled         */
>  #define MIPS_HFLAG_RE     0x00100 /* Reversed endianness                */
> -#define MIPS_HFLAG_UX     0x00200 /* 64-bit user mode                   */
> +#define MIPS_HFLAG_X      0x00200 /* 64-bit mode enabled                */
>  #define MIPS_HFLAG_M16    0x00400 /* MIPS16 mode flag                   */
>  #define MIPS_HFLAG_M16_SHIFT 10
>      /* If translation is interrupted between the branch instruction and
> @@ -721,7 +721,7 @@ static inline void compute_hflags(CPUMIPSState *env)
>  {
>      env->hflags &= ~(MIPS_HFLAG_COP1X | MIPS_HFLAG_64 | MIPS_HFLAG_CP0 |
>                       MIPS_HFLAG_F64 | MIPS_HFLAG_FPU | MIPS_HFLAG_KSU |
> -                     MIPS_HFLAG_UX | MIPS_HFLAG_DSP | MIPS_HFLAG_DSPR2);
> +                     MIPS_HFLAG_X | MIPS_HFLAG_DSP | MIPS_HFLAG_DSPR2);
>      if (!(env->CP0_Status & (1 << CP0St_EXL)) &&
>          !(env->CP0_Status & (1 << CP0St_ERL)) &&
>          !(env->hflags & MIPS_HFLAG_DM)) {
> @@ -733,8 +733,14 @@ static inline void compute_hflags(CPUMIPSState *env)
>          (env->CP0_Status & (1 << CP0St_UX))) {
>          env->hflags |= MIPS_HFLAG_64;
>      }
> -    if (env->CP0_Status & (1 << CP0St_UX)) {
> -        env->hflags |= MIPS_HFLAG_UX;
> +
> +    if ((((env->hflags & MIPS_HFLAG_KSU) == MIPS_HFLAG_UM) &&
> +         (env->CP0_Status & (1 << CP0St_UX))) ||
> +        (((env->hflags & MIPS_HFLAG_KSU) == MIPS_HFLAG_SM) &&
> +         (env->CP0_Status & (1 << CP0St_SX))) ||
> +        (((env->hflags & MIPS_HFLAG_KSU) == MIPS_HFLAG_KM) &&
> +         (env->CP0_Status & (1 << CP0St_KX)))) {
> +        env->hflags |= MIPS_HFLAG_X;
>      }
>  #endif
>      if ((env->CP0_Status & (1 << CP0St_CU0)) ||
> diff --git a/target-mips/translate.c b/target-mips/translate.c
> index 2e94375..6d294e1 100644
> --- a/target-mips/translate.c
> +++ b/target-mips/translate.c
> @@ -1373,17 +1373,27 @@ generate_exception (DisasContext *ctx, int excp)
>      gen_helper_0e0i(raise_exception, excp);
>  }
>  
> +#if defined(TARGET_MIPS64)
> +static inline int is_wrapping_needed(DisasContext *ctx)
> +{
> +    if (!(ctx->hflags & MIPS_HFLAG_X)) {
> +        /* If not R6 then wrap only in User Mode */
> +        if ((ctx->insn_flags & ISA_MIPS64R6) ||
> +            ((ctx->hflags & MIPS_HFLAG_KSU) == MIPS_HFLAG_UM)) {
> +            return 1;
> +        }
> +    }
> +    return 0;
> +}
> +#endif

As Richard said, this code should be moved above, and the HFLAG semantic
should be changed to "address wrapping needed". The current code is
already wrong (and I am afraid I am the author...).

So this could be done by renaming the HFLAG to for exemple
MIPS_HFLAG_AWRAP, and checking only for this flag in gen_op_addr_add.
Then the checks have to be adapted in compute_hflags, including the R6
case.

>  /* Addresses computation */
>  static inline void gen_op_addr_add (DisasContext *ctx, TCGv ret, TCGv arg0, 
> TCGv arg1)
>  {
>      tcg_gen_add_tl(ret, arg0, arg1);
>  
>  #if defined(TARGET_MIPS64)
> -    /* For compatibility with 32-bit code, data reference in user mode
> -       with Status_UX = 0 should be casted to 32-bit and sign extended.
> -       See the MIPS64 PRA manual, section 4.10. */
> -    if (((ctx->hflags & MIPS_HFLAG_KSU) == MIPS_HFLAG_UM) &&
> -        !(ctx->hflags & MIPS_HFLAG_UX)) {
> +    if (is_wrapping_needed(ctx)) {
>          tcg_gen_ext32s_i64(ret, ret);
 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net