Re: [RFC PATCH v4 2/7] rust: add bindgen step as a meson dependency

["Alex Bennée" <alex.bennee@linaro.org>]

Alex Bennée <alex.bennee@linaro.org> writes:

> Manos Pitsidianakis <manos.pitsidianakis@linaro.org> writes:
>
>> Add mechanism to generate rust hw targets that depend on a custom
>> bindgen target for rust bindings to C.
>>
>> This way bindings will be created before the rust crate is compiled.
>>
>> The bindings will end up in BUILDDIR/{target}-generated.rs and have the same name
>> as a target:
>>
>> ninja aarch64-softmmu-generated.rs
>>
>> The way the bindings are generated is:
>>
>> 1. All required C headers are included in a single file, in our case
>>    rust/wrapper.h for convenience. Otherwise we'd have to provide a list
>>    of headers every time to the bindgen tool.
>>
>> 2. Meson creates a generated_rs target that runs bindgen making sure
>>    the architecture etc header dependencies are present.
>>
>> 3. The generated_rs target takes a list of files, type symbols,
>>    function symbols to block from being generated. This is not necessary
>>    for the bindings to work, but saves us time and space.
>>
>> 4. Meson creates rust hardware target dependencies from the rust_targets
>>    dictionary defined in rust/meson.build.
>>
>>    Since we cannot declare a dependency on generated_rs before it is
>>    declared in meson.build, the rust crate targets must be defined after
>>    the generated_rs target for each target architecture is defined. This
>>    way meson sets up the dependency tree properly.
>>
>> 5. After compiling each rust crate with the cargo_wrapper.py script,
>>    its static library artifact is linked as a `whole-archive` with the
>>    final binary.
>>
>> Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
> <snip>
>> +
>> +msrv = {
>> +  'rustc': '1.77.2',
>> +  'cargo': '1.77.2',
>> +  'bindgen': '0.69.4',
>> +}
>
> This is still pretty bleeding edge (it even tripped up on the
> .cargo/bin/cargo I have installed). This needs to be set to the
> baseline which from:
>
>   https://wiki.qemu.org/RustInQemu/2022
>
> Looks to be 1.24.0 for rustc and I guess even lower for cargo (Debian
> says 0.66.0). While it might make sense to delay merging if we are
> waiting for one distro to produce a new LTS we shouldn't be needing
> rustup by default.

Also bindgen, do we need such a new one? On Trixie:

  Message:

  ../../rust/meson.build:41:4: ERROR: Problem encountered: bindgen version 0.66.1 is unsupported: Please upgrade to at least 0.69.4

  A full log can be found at /home/alex/lsrc/qemu.git/builds/rust/meson-logs/meson-log.txt

  ERROR: meson setup failed

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro