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

[Danilo Krummrich <dakr@kernel.org>]

On Sat, Sep 28, 2024 at 08:43:57PM +0100, Gary Guo wrote:
> 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?

It's only about those two lines, right? I can only remove the `new_uninit` and
leave `rust_allowed_features :=` and leave...

> 
> 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) \

...this line, I guess?

> 
> 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,
> >              )
> >  
>