Re: [PATCH] aarch64: Fix test_dfp_17.c for big-endian [PR 107604]

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 22/11/2022 09:01, Christophe Lyon via Gcc-patches wrote:
> gcc.target/aarch64/aapcs64/test_dfp_17.c has been failing on
> big-endian, because the _Decimal32 on-stack argument is not padded in
> the same direction depending on endianness.
> 
> This patch fixes the testcase so that it expects the argument in the
> right stack location, similarly to what other tests do in the same
> directory.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR target/107604
> 	* gcc.target/aarch64/aapcs64/test_dfp_17.c: Fix for big-endian.
> ---
>   gcc/testsuite/gcc.target/aarch64/aapcs64/test_dfp_17.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/gcc/testsuite/gcc.target/aarch64/aapcs64/test_dfp_17.c b/gcc/testsuite/gcc.target/aarch64/aapcs64/test_dfp_17.c
> index 22dc462bf7c..3c45f715cf7 100644
> --- a/gcc/testsuite/gcc.target/aarch64/aapcs64/test_dfp_17.c
> +++ b/gcc/testsuite/gcc.target/aarch64/aapcs64/test_dfp_17.c
> @@ -32,6 +32,10 @@ struct z b = { 9.0dd, 10.0dd, 11.0dd, 12.0dd };
>     ANON(struct z, a, D1)
>     ANON(struct z, b, STACK)
>     ANON(int , 5, W0)
> +#ifndef __AAPCS64_BIG_ENDIAN__
>     ANON(_Decimal32, f1, STACK+32) /* Note: no promotion to _Decimal64.  */
> +#else
> +  ANON(_Decimal32, f1, STACK+36) /* Note: no promotion to _Decimal64.  */
> +#endif
>     LAST_ANON(_Decimal64, 0.5dd, STACK+40)
>   #endif

Why would a Decimal32 change stack placement based on the endianness? 
Isn't it a 4-byte object?