Re: [PATCH-for-9.0 04/10] hw/xen: Factor xen_arch_align_ioreq_data() out of handle_ioreq()

[Woodhouse, David]

On 13 Nov 2023 10:22, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:

Per commit f17068c1c7 ("xen-hvm: reorganize xen-hvm and move common
function to xen-hvm-common"), handle_ioreq() is expected to be
target-agnostic. However it uses 'target_ulong', which is a target
specific definition.

In order to compile this file once for all targets, factor the
target-specific code out of handle_ioreq() as a per-target handler
called xen_arch_align_ioreq_data().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
Should we have a 'unsigned qemu_target_long_bits();' helper
such qemu_target_page_foo() API and target_words_bigendian()?

It can be more fun than that though. What about qemu_target_alignof_uint64() for example, which differs between i386 and x86_64 and causes even structs with *explicitly* sized fields to differ because of padding.

I'd *love* to see this series as a step towards my fantasy of being able to support Xen under TCG. After all, without that what's the point in being target-agnostic?

However, I am mildly concerned that some of these files are accidentally using the host ELF ABI, perhaps with explicit management of 32-bit compatibility, and the target-agnosticity is purely an illusion?

See the "protocol" handling and the three ABIs for the ring in xen-block, for example.

Can we be explicit about what's expected to work here and what's not in scope? 

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