Re: [PATCH 2/2] target/m68k: add M68K_FEATURE_NO_DALIGN feature

[Laurent Vivier]

Le 07/03/2021 à 21:26, Mark Cave-Ayland a écrit :
> According to the M68040UM Appendix D the requirement for data accesses to be
> word aligned is only for the 68000, 68008 and 68010 CPUs. Later CPUs from the
> 68020 onwards will allow unaligned data accesses but at the cost of being less
> efficient.
> 
> Add a new M68K_FEATURE_NO_DALIGN feature to specify that data accesses are not
> required to be word aligned, and don't perform the alignment on the stack
> pointer when taking an exception if this feature is not selected.
> 
> This is required because the MacOS DAFB driver attempts to call an A-trap
> with a byte-aligned stack pointer during initialisation and without this the
> stack pointer is off by one when the A-trap returns.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
>  target/m68k/cpu.c       | 1 +
>  target/m68k/cpu.h       | 1 +
>  target/m68k/op_helper.c | 5 ++++-
>  3 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/target/m68k/cpu.c b/target/m68k/cpu.c
> index 37d2ed9dc7..ea51753eb0 100644
> --- a/target/m68k/cpu.c
> +++ b/target/m68k/cpu.c
> @@ -161,6 +161,7 @@ static void m68020_cpu_initfn(Object *obj)
>      m68k_set_feature(env, M68K_FEATURE_CAS);
>      m68k_set_feature(env, M68K_FEATURE_CHK2);
>      m68k_set_feature(env, M68K_FEATURE_MSP);
> +    m68k_set_feature(env, M68K_FEATURE_NO_DALIGN);
>  }
>  
>  /*
> diff --git a/target/m68k/cpu.h b/target/m68k/cpu.h
> index 7c3feeaf8a..1e0876bba8 100644
> --- a/target/m68k/cpu.h
> +++ b/target/m68k/cpu.h
> @@ -505,6 +505,7 @@ enum m68k_features {
>      M68K_FEATURE_CHK2,  /* CHK2 insn. (680[2346]0, and CPU32) */
>      M68K_FEATURE_MOVEP, /* MOVEP insn. (680[01234]0, and CPU32) */
>      M68K_FEATURE_MOVEC, /* MOVEC insn. (from 68010) */
> +    M68K_FEATURE_NO_DALIGN, /* Unaligned data accesses (680[2346]0) */
>  };
>  
>  static inline int m68k_feature(CPUM68KState *env, int feature)
> diff --git a/target/m68k/op_helper.c b/target/m68k/op_helper.c
> index 59a6448296..71b3df0910 100644
> --- a/target/m68k/op_helper.c
> +++ b/target/m68k/op_helper.c
> @@ -348,7 +348,10 @@ static void m68k_interrupt_all(CPUM68KState *env, int 
> is_hw)
>      cpu_m68k_set_sr(env, sr);
>      sp = env->aregs[7];
>  
> -    sp &= ~1;
> +    if (!m68k_feature(env, M68K_FEATURE_NO_DALIGN)) {
> +        sp &= ~1;
> +    }
> +
>      if (cs->exception_index == EXCP_ACCESS) {
>          if (env->mmu.fault) {
>              cpu_abort(cs, "DOUBLE MMU FAULT\n");
> 

Reviewed-by: Laurent Vivier <laurent@vivier.eu>