rust: introduce alternative implementation of offset_of!

offset_of! was stabilized in Rust 1.77.0. Use an alternative implemenation
that was found on the Rust forums, and whose author agreed to lic

rust: introduce alternative implementation of offset_of!

offset_of! was stabilized in Rust 1.77.0. Use an alternative implemenation
that was found on the Rust forums, and whose author agreed to license as
MIT for use in QEMU.

The alternative allows only one level of field access, but apart
from this can be used just by replacing core::mem::offset_of! with
qemu_api::offset_of!.

The actual implementation of offset_of! is done in a declarative macro,
but for simplicity and to avoid introducing an extra level of indentation,
the trigger is a procedural macro #[derive(offsets)].

The procedural macro is perhaps a bit overengineered, but it helps
introducing some idioms that will be useful in the future as well.

Signed-off-by: Junjie Mao <junjie.mao@hotmail.com>
Co-developed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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rust: cleanup module_init!, use it from #[derive(Object)]

Remove the duplicate code by using the module_init! macro; at the same time,
simplify how module_init! is used, by taking inspiration from t

rust: cleanup module_init!, use it from #[derive(Object)]

Remove the duplicate code by using the module_init! macro; at the same time,
simplify how module_init! is used, by taking inspiration from the implementation
of #[derive(Object)].

Reviewed-by: Junjie Mao <junjie.mao@hotmail.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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rust: modernize link_section usage for ELF platforms

Some newer ABI implementations do not provide .ctors; and while
some linkers rewrite .ctors into .init_array, not all of them do.
Use the newer .

rust: modernize link_section usage for ELF platforms

Some newer ABI implementations do not provide .ctors; and while
some linkers rewrite .ctors into .init_array, not all of them do.
Use the newer .init_array ABI, which works more reliably, and
apply it to all non-Apple, non-Windows platforms.

This is similar to how the ctor crate operates; without this change,
"#[derive(Object)]" does not work on Fedora 41.

Reviewed-by: Junjie Mao <junjie.mao@hotmail.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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rust: add utility procedural macro crate

This commit adds a helper crate library, qemu-api-macros for derive (and
other procedural) macros to be used along qemu-api.

It needs to be a separate libra

rust: add utility procedural macro crate

This commit adds a helper crate library, qemu-api-macros for derive (and
other procedural) macros to be used along qemu-api.

It needs to be a separate library because in Rust, procedural macros, or
macros that can generate arbitrary code, need to be special separate
compilation units.

Only one macro is introduced in this patch, #[derive(Object)]. It
generates a constructor to register a QOM TypeInfo on init and it must
be used on types that implement qemu_api::definitions::ObjectImpl trait.

Reviewed-by: Junjie Mao <junjie.mao@hotmail.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Link: https://lore.kernel.org/r/dd645642406a6dc2060c6f3f17db2bc77ed67b59.1727961605.git.manos.pitsidianakis@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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