Re: [PATCH v7 25/26] kbuild: rust: remove the `alloc` crate and `GlobalAlloc`

[Gary Guo <gary@garyguo.net>]

On Thu, 12 Sep 2024 00:53:01 +0200
Danilo Krummrich <dakr@kernel.org> wrote:

> Now that we have our own `Allocator`, `Box` and `Vec` types we can remove
> Rust's `alloc` crate and the `new_uninit` unstable feature.
> 
> Also remove `Kmalloc`'s `GlobalAlloc` implementation -- we can't remove
> this in a separate patch, since the `alloc` crate requires a
> `#[global_allocator]` to set, that implements `GlobalAlloc`.
> 
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  rust/Makefile                     | 43 +++++----------------
>  rust/exports.c                    |  1 -
>  rust/kernel/alloc/allocator.rs    | 63 +------------------------------
>  scripts/Makefile.build            |  7 +---
>  scripts/generate_rust_analyzer.py | 11 +-----
>  5 files changed, 15 insertions(+), 110 deletions(-)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 72b1232b1f7d..529ec5972e55 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -262,18 +262,13 @@ $(obj)/%.lst: $(obj)/%.c FORCE
>  
>  # Compile Rust sources (.rs)
>  # ---------------------------------------------------------------------------
> -
> -rust_allowed_features := new_uninit
> -

Would it make sense to throw in a soon-to-be-stable (or
already-stable-but-beyond-min-rust-version) feature here to not have to
remove the build system support for unstable feature directly?

For example, I know that const_refs_to_static might be added here
soon-ish.

>  # `--out-dir` is required to avoid temporaries being created by `rustc` in the
>  # current working directory, which may be not accessible in the out-of-tree
>  # modules case.
>  rust_common_cmd = \
>  	RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \
> -	-Zallow-features=$(rust_allowed_features) \

I think this actually allow all features instead of allowing none.

>  	-Zcrate-attr=no_std \
> -	-Zcrate-attr='feature($(rust_allowed_features))' \
> -	-Zunstable-options --extern force:alloc --extern kernel \
> +	-Zunstable-options --extern kernel \
>  	--crate-type rlib -L $(objtree)/rust/ \
>  	--crate-name $(basename $(notdir $@)) \
>  	--sysroot=/dev/null \
> diff --git a/scripts/generate_rust_analyzer.py b/scripts/generate_rust_analyzer.py
> index d2bc63cde8c6..09e1d166d8d2 100755
> --- a/scripts/generate_rust_analyzer.py
> +++ b/scripts/generate_rust_analyzer.py
> @@ -64,13 +64,6 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs):
>          [],
>      )
>  
> -    append_crate(
> -        "alloc",
> -        sysroot_src / "alloc" / "src" / "lib.rs",
> -        ["core", "compiler_builtins"],
> -        cfg=crates_cfgs.get("alloc", []),
> -    )
> -
>      append_crate(
>          "macros",
>          srctree / "rust" / "macros" / "lib.rs",
> @@ -96,7 +89,7 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs):
>      append_crate(
>          "kernel",
>          srctree / "rust" / "kernel" / "lib.rs",
> -        ["core", "alloc", "macros", "build_error", "bindings"],
> +        ["core", "macros", "build_error", "bindings"],
>          cfg=cfg,
>      )
>      crates[-1]["source"] = {
> @@ -133,7 +126,7 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs):
>              append_crate(
>                  name,
>                  path,
> -                ["core", "alloc", "kernel"],
> +                ["core", "kernel"],
>                  cfg=cfg,
>              )
>