Re: Invalid ARM instruction for clang-compiled Android code

[Michael Goffioul <michael.goffioul@gmail.com>]

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On Fri, Nov 15, 2019 at 6:03 AM Peter Maydell <peter.maydell@linaro.org>
wrote:

> Richard, I think we're tripping over the check you added
> in commit af2882289951e. Specifically:
>
> +    /* We UNDEF for these UNPREDICTABLE cases.  */
> +    if (a->rd == 15 || a->rn == 15 || a->rt == 15
> +        || a->rd == a->rn || a->rd == a->rt
> +        || (s->thumb && (a->rd == 13 || a->rt == 13))
> +        || (mop == MO_64
> +            && (a->rt2 == 15
> +                || a->rd == a->rt2 || a->rt == a->rt2
> +                || (s->thumb && a->rt2 == 13)))) {
> +        unallocated_encoding(s);
> +        return true;
> +    }
>
> in the mop == MO_64 subclause we check for
>  a->rt == a->rt2
> so we will UNDEF for rt == rt2, as in this example. But the
> pseudocode in the spec doesn't say that rt == rt2 is
> an UNPREDICTABLE case. (It is an UNDPREDICTABLE
> case for LDREXD, but STREXD lets you write the same
> register twice if you want to.) Or am I misreading this?
>

BTW, I can confirm that removing the check "a->rt == a->rt2" seems to fix
my problem.

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