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

[Danilo Krummrich <dakr@kernel.org>]

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@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?

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,
>>>               )
>>>   
>>