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

[Danilo Krummrich]

On 9/29/24 5:17 PM, Danilo Krummrich wrote:
> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > >   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?

Seems like I can't, it blows up with an empty feature list. I'll keep it as it 
is for now. Shouldn't be a big deal to add it again, once needed.

> > 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,
> > >               )
> > >