Re: [PATCH] sh4: mac.w: memory accesses are 16-bit words

[Philippe Mathieu-Daudé]

On 2/4/24 11:37, Zack Buhman wrote:
> Before this change, executing a code sequence such as:
>
>             mova   tblm,r0
>             mov    r0,r1
>             mova   tbln,r0
>             clrs
>             clrmac
>             mac.w  @r0+,@r1+
>             mac.w  @r0+,@r1+
>
>             .align 4
>    tblm:    .word  0x1234
>             .word  0x5678
>    tbln:    .word  0x9abc
>             .word  0xdefg
>
> Does not result in correct behavior:
>
> Expected behavior:
>    first macw : macl = 0x1234 * 0x9abc + 0x0
>                 mach = 0x0
>
>    second macw: macl = 0x5678 * 0xdefg + 0xb00a630
>                 mach = 0x0
>
> Observed behavior (qemu-sh4eb, prior to this commit):
>
>    first macw : macl = 0x5678 * 0xdefg + 0x0
>                 mach = 0x0
>
>    second macw: (unaligned longword memory access, SIGBUS)
>
> Various SH-4 ISA manuals also confirm that `mac.w` is a 16-bit word memory
> access, not a 32-bit longword memory access.
>
> Signed-off-by: Zack Buhman <zack@buhman.org>
> ---
>   target/sh4/translate.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/target/sh4/translate.c b/target/sh4/translate.c
> index a9b1bc7524..6643c14dde 100644
> --- a/target/sh4/translate.c
> +++ b/target/sh4/translate.c
> @@ -816,10 +816,10 @@ static void _decode_opc(DisasContext * ctx)
>               TCGv arg0, arg1;
>               arg0 = tcg_temp_new();
>               tcg_gen_qemu_ld_i32(arg0, REG(B7_4), ctx->memidx,
> -                                MO_TESL | MO_ALIGN);
> +                                MO_TESW | MO_ALIGN);
>               arg1 = tcg_temp_new();
>               tcg_gen_qemu_ld_i32(arg1, REG(B11_8), ctx->memidx,
> -                                MO_TESL | MO_ALIGN);
> +                                MO_TESW | MO_ALIGN);

Apparently invalid since its introduction in commit fdf9b3e831.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

>               gen_helper_macw(tcg_env, arg0, arg1);
>               tcg_gen_addi_i32(REG(B11_8), REG(B11_8), 2);
>               tcg_gen_addi_i32(REG(B7_4), REG(B7_4), 2);