On 28/08/2023 17.48, Philippe Mathieu-Daudé wrote:
On 28/8/23 14:41, Thomas Huth wrote:
On 28/08/2023 14.19, Philippe Mathieu-Daudé wrote:
Hi Thomas,
On 25/8/23 19:51, Thomas Huth wrote:
There is an easier way to get a value that can be used to decide
whether the target is big endian or not: Simply use the
target_words_bigendian() function instead.
Signed-off-by: Thomas Huth <th...@redhat.com>
---
hw/mips/jazz.c | 10 ++--------
1 file changed, 2 insertions(+), 8 deletions(-)
@@ -157,12 +157,6 @@ static void mips_jazz_init(MachineState *machine,
[JAZZ_PICA61] = {33333333, 4},
};
-#if TARGET_BIG_ENDIAN
- big_endian = 1;
-#else
- big_endian = 0;
-#endif
-
if (machine->ram_size > 256 * MiB) {
error_report("RAM size more than 256Mb is not supported");
exit(EXIT_FAILURE);
@@ -301,7 +295,7 @@ static void mips_jazz_init(MachineState *machine,
dev = qdev_new("dp8393x");
qdev_set_nic_properties(dev, nd);
qdev_prop_set_uint8(dev, "it_shift", 2);
- qdev_prop_set_bit(dev, "big_endian", big_endian > 0);
+ qdev_prop_set_bit(dev, "big_endian",
target_words_bigendian());
IIRC last time I tried that Peter pointed me at the documentation:
/**
* target_words_bigendian:
* Returns true if the (default) endianness of the target is big endian,
* false otherwise. Note that in target-specific code, you can use
* TARGET_BIG_ENDIAN directly instead. On the other hand, common
* code should normally never need to know about the endianness of the
* target, so please do *not* use this function unless you know very
* well what you are doing!
*/
(Commit c95ac10340 "cpu: Provide a proper prototype for
target_words_bigendian() in a header")
Should we update the comment?
What would you change? My motivation here was mainly to decrease the size
of the code - I think it's way more complicated via the #if + extra
variable compared to simply calling target_words_bigendian(), isn't it? I
think the diffstat says it all...
Is the comment misleading then? Why not decrease the code
size using target_words_bigendian() in all the similar cases?
$ git grep -A4 'if TARGET_BIG_ENDIAN' hw/
hw/microblaze/boot.c:145:#if TARGET_BIG_ENDIAN
hw/microblaze/boot.c-146- big_endian = 1;
hw/microblaze/boot.c-147-#endif
--
hw/mips/jazz.c:160:#if TARGET_BIG_ENDIAN
hw/mips/jazz.c-161- big_endian = 1;
hw/mips/jazz.c-162-#else
hw/mips/jazz.c-163- big_endian = 0;
hw/mips/jazz.c-164-#endif
--
hw/mips/malta.c:378:#if TARGET_BIG_ENDIAN
hw/mips/malta.c-379- val = 0x00000012;
hw/mips/malta.c-380-#else
hw/mips/malta.c-381- val = 0x00000010;
hw/mips/malta.c-382-#endif
--
hw/mips/malta.c:631:#if TARGET_BIG_ENDIAN
hw/mips/malta.c-632-#define cpu_to_gt32(x) (x)
hw/mips/malta.c-633-#else
hw/mips/malta.c-634-#define cpu_to_gt32(x) bswap32(x)
hw/mips/malta.c-635-#endif
If it's just about a variable that gets initialized to 0 or 1, replacing it
with target_words_bigendian() certainly make a lot of sense. Not sure about
this spot in malta.c, though, this is a bit different since it declares a
macro instead.
So within hw/ I'd restrict target_words_bigendian() use to
MachineClass::init() handlers, and prohibit TARGET_BIG_ENDIAN
from hw/. Only use in softmmu/, target, *-user/. If we agree
we can rewrite the comment, removing the "do *not* use this
function unless you know very well what you are doing!" which
is hard to interpret IMHO.
Ok, now I got you, I think. Yes, I agree we should update the comment to say
that it should not be used in *devices* (unless you know what you're doing,
e.g. in virtio code). I just also found the original discussion which was
about the same thoughts:
https://lists.nongnu.org/archive/html/qemu-devel/2018-10/msg00939.html
Thomas
