(sorry, posted too quick)
On 6/2/25 19:24, Philippe Mathieu-Daudé wrote:
+Michal
On 6/2/25 19:06, Daniel P. Berrangé wrote:
On Thu, Feb 06, 2025 at 06:49:38PM +0100, Philippe Mathieu-Daudé wrote:
On 6/2/25 18:12, Daniel P. Berrangé wrote:
On Thu, Feb 06, 2025 at 04:04:20PM +0100, Philippe Mathieu-Daudé wrote:
On 6/2/25 15:31, Daniel P. Berrangé wrote:
On Thu, Feb 06, 2025 at 02:53:58PM +0100, Philippe Mathieu-Daudé
wrote:
Hi Daniel,
On 6/2/25 14:20, Daniel P. Berrangé wrote:
On Thu, Feb 06, 2025 at 02:10:47PM +0100, Philippe Mathieu-Daudé
wrote:
Introduce an abstract machine parent class which defines
the 'little_endian' property. Duplicate the current machine,
which endian is tied to the binary endianness, to one big
endian and a little endian machine; updating the machine
description. Keep the current default machine for each binary.
'petalogix-s3adsp1800' machine is aliased as:
- 'petalogix-s3adsp1800-be' on big-endian binary,
- 'petalogix-s3adsp1800-le' on little-endian one.
Does it makes sense to expose these as different machine types ?
If all the HW is identical in both cases, it feels like the
endianness could just be a bool property of the machine type,
rather than a new machine type.
Our test suites expect "qemu-system-foo -M bar" to work out of
the box, we can not have non-default properties.
(This is related to the raspberry pi discussion in
https://lore.kernel.org/qemu-devel/20250204002240.97830-1-
phi...@linaro.org/).
My plan is to deprecate 'petalogix-s3adsp1800', so once we
remove it we can merge both qemu-system-microblaze and
qemu-system-microblazeel into a single binary.
If you don't want to add more machines, what should be the
endianness of the 'petalogix-s3adsp1800' machine in a binary
with no particular endianness? Either we add for explicit
endianness (fixing test suites) or we add one machine for
each endianness; I fail to see other options not too
confusing for our users.
We would pick an arbitrary endianness of our choosing
I guess. How does this work in physical machines ? Is
the choice of endianess a firmware setting, or a choice
by the vendor when manufacturing in some way ?
Like MIPS*, SH4* and Xtensa*, it is a jumper on the board
(wired to a CPU pin which is sampled once at cold reset).
That makes me thing even more it is just a machine type property.
I'm happy with a machine property, this was even my first approach
using OnOffAuto until I ran the test-suite and have qom-introspection
failing.
What should be the default?
Per the SH4 datasheet:
Bit 31—Endian Flag (ENDIAN): Samples the value of the endian
specification external pin (MD5) in a power-on reset by the
RESET pin. The endian mode of all spaces is determined by this
bit. ENDIAN is a read-only bit.
There is no default per the spec, and I believe using one is
a mistake.
If it is left as an unspecified choice in the spec, then I would
presume HW vendors are picking an option based on what they
expect "most" common usage to be amongst their customers. IOW,
if we know of typically used guest OS prefer big or little, that
could influence our choice.
Please have a look at this thread:
https://lore.kernel.org/qemu-devel/
d3346a55-584b-427b-8c87-32f7411a9...@amd.com/
Per Michal:
Truth is that I am not aware about anybody configuring MB to big
endian and we are on AXI for quite a long time. There is still
code in Linux kernel for it but I can't see any reason to keep it
around. I don't think that make sense to keep big endian
configurations alive at all.
So with that in mind, using a default of little-endian=true for
MicroBlaze seems safe as of 2025.
For MIPS, big-endian was the default but as the industry shifted,
it stayed big-endian on low-end 32-bit cores but mostly became
little-endian on high-end 64-bit cores.
For Renesas RX, the "Endian" section in the "CPU" chapter of the
hardware manual mentions:
Both big and little endian are supported for the treatment of data,
and the endian is switched by changing the setting on a mode pin (MDE)
at the time of a power-on reset.
SH-4 "is bi-endian, running in either big-endian or little-endian byte
ordering."
