Re: [PATCH 1/2] tests/tcg/multiarch: Make the system memory test work on big-endian

[Peter Maydell]

On Sat, 22 Apr 2023 at 12:03, Thomas Weißschuh <thomas@t-8ch.de> wrote:
>
> On 2023-04-22 02:58:07+0200, Ilya Leoshkevich wrote:
> > Make sure values are stored in memory as little-endian regardless of
> > the host endianness.
> >
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> > ---
> >  tests/tcg/multiarch/system/memory.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/tests/tcg/multiarch/system/memory.c 
> > b/tests/tcg/multiarch/system/memory.c
> > index 214f7d4f54b..8ef6666b440 100644
> > --- a/tests/tcg/multiarch/system/memory.c
> > +++ b/tests/tcg/multiarch/system/memory.c
> > @@ -121,6 +121,9 @@ static void init_test_data_u16(int offset)
> >      for (i = 0; i < max; i++) {
> >          uint8_t low = count++, high = count++;
> >          word = BYTE_SHIFT(high, 1) | BYTE_SHIFT(low, 0);
> > +#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
> > +        word = __builtin_bswap16(word);
> > +#endif
>
> These looks like a usecase for cpu_to_le16() and friends.

I'm not sure this test code has direct access to those, but
the general principle is right.

It is particularly odd that we carefully manually put
together a word by shifting-and-ORing together the
various bytes in it, and then separately do a byteswap.

thanks
-- PMM