[PATCH v5 25/26] kbuild: rust: remove the `alloc` crate and `GlobalAlloc`

Danilo Krummrich
2024-08-12T18:26:23Z

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 | 44 ++++++-----------------
rust/exports.c | 1 -
rust/kernel/alloc/allocator.rs | 59 ++-----------------------------
scripts/Makefile.build | 7 +---
scripts/generate_rust_analyzer.py | 11 ++----
5 files changed, 15 insertions(+), 107 deletions(-)

diff --git a/rust/Makefile b/rust/Makefile
index 1f10f92737f2..8900c3d06573 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -15,9 +15,8 @@ always-$(CONFIG_RUST) += libmacros.so
no-clean-files += libmacros.so

always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs
-obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
-always-$(CONFIG_RUST) += exports_alloc_generated.h exports_bindings_generated.h \
- exports_kernel_generated.h
+obj-$(CONFIG_RUST) += bindings.o kernel.o
+always-$(CONFIG_RUST) += exports_bindings_generated.h exports_kernel_generated.h

always-$(CONFIG_RUST) += uapi/uapi_generated.rs
obj-$(CONFIG_RUST) += uapi.o
@@ -53,11 +52,6 @@ endif
core-cfgs = \
--cfg no_fp_fmt_parse

-alloc-cfgs = \
- --cfg no_global_oom_handling \
- --cfg no_rc \
- --cfg no_sync
-
quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
cmd_rustdoc = \
OBJTREE=$(abspath $(objtree)) \
@@ -80,7 +74,7 @@ quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
# command-like flags to solve the issue. Meanwhile, we use the non-custom case
# and then retouch the generated files.
rustdoc: rustdoc-core rustdoc-macros rustdoc-compiler_builtins \
- rustdoc-alloc rustdoc-kernel
+ rustdoc-kernel
$(Q)cp $(srctree)/Documentation/images/logo.svg $(rustdoc_output)/static.files/
$(Q)cp $(srctree)/Documentation/images/COPYING-logo $(rustdoc_output)/static.files/
$(Q)find $(rustdoc_output) -name '*.html' -type f -print0 | xargs -0 sed -Ei \
@@ -104,20 +98,11 @@ rustdoc-core: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
rustdoc-compiler_builtins: $(src)/compiler_builtins.rs rustdoc-core FORCE
+$(call if_changed,rustdoc)

-# We need to allow `rustdoc::broken_intra_doc_links` because some
-# `no_global_oom_handling` functions refer to non-`no_global_oom_handling`
-# functions. Ideally `rustdoc` would have a way to distinguish broken links
-# due to things that are "configured out" vs. entirely non-existing ones.
-rustdoc-alloc: private rustc_target_flags = $(alloc-cfgs) \
- -Arustdoc::broken_intra_doc_links
-rustdoc-alloc: $(RUST_LIB_SRC)/alloc/src/lib.rs rustdoc-core rustdoc-compiler_builtins FORCE
- +$(call if_changed,rustdoc)
-
-rustdoc-kernel: private rustc_target_flags = --extern alloc \
+rustdoc-kernel: private rustc_target_flags = \
--extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so \
--extern bindings --extern uapi
rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-macros \
- rustdoc-compiler_builtins rustdoc-alloc $(obj)/libmacros.so \
+ rustdoc-compiler_builtins $(obj)/libmacros.so \
$(obj)/bindings.o FORCE
+$(call if_changed,rustdoc)

@@ -161,7 +146,7 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
OBJTREE=$(abspath $(objtree)) \
$(RUSTDOC) --test $(rust_flags) \
- -L$(objtree)/$(obj) --extern alloc --extern kernel \
+ -L$(objtree)/$(obj) --extern kernel \
--extern build_error --extern macros \
--extern bindings --extern uapi \
--no-run --crate-name kernel -Zunstable-options \
@@ -197,7 +182,7 @@ rusttest-macros: $(src)/macros/lib.rs FORCE
+$(call if_changed,rustc_test)
+$(call if_changed,rustdoc_test)

-rusttest-kernel: private rustc_target_flags = --extern alloc \
+rusttest-kernel: private rustc_target_flags = \
--extern build_error --extern macros --extern bindings --extern uapi
rusttest-kernel: $(src)/kernel/lib.rs \
rusttestlib-build_error rusttestlib-macros rusttestlib-bindings \
@@ -310,9 +295,6 @@ quiet_cmd_exports = EXPORTS $@
$(obj)/exports_core_generated.h: $(obj)/core.o FORCE
$(call if_changed,exports)

-$(obj)/exports_alloc_generated.h: $(obj)/alloc.o FORCE
- $(call if_changed,exports)
-
$(obj)/exports_bindings_generated.h: $(obj)/bindings.o FORCE
$(call if_changed,exports)

@@ -348,7 +330,7 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L

rust-analyzer:
$(Q)$(srctree)/scripts/generate_rust_analyzer.py \
- --cfgs='core=$(core-cfgs)' --cfgs='alloc=$(alloc-cfgs)' \
+ --cfgs='core=$(core-cfgs)' \
$(realpath $(srctree)) $(realpath $(objtree)) \
$(RUST_LIB_SRC) $(KBUILD_EXTMOD) > \
$(if $(KBUILD_EXTMOD),$(extmod_prefix),$(objtree))/rust-project.json
@@ -380,12 +362,6 @@ $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
$(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
+$(call if_changed_dep,rustc_library)

-$(obj)/alloc.o: private skip_clippy = 1
-$(obj)/alloc.o: private skip_flags = -Wunreachable_pub
-$(obj)/alloc.o: private rustc_target_flags = $(alloc-cfgs)
-$(obj)/alloc.o: $(RUST_LIB_SRC)/alloc/src/lib.rs $(obj)/compiler_builtins.o FORCE
- +$(call if_changed_dep,rustc_library)
-
$(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
+$(call if_changed_dep,rustc_library)

@@ -400,9 +376,9 @@ $(obj)/uapi.o: $(src)/uapi/lib.rs \
$(obj)/uapi/uapi_generated.rs FORCE
+$(call if_changed_dep,rustc_library)

-$(obj)/kernel.o: private rustc_target_flags = --extern alloc \
+$(obj)/kernel.o: private rustc_target_flags = \
--extern build_error --extern macros --extern bindings --extern uapi
-$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
+$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/build_error.o \
$(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE
+$(call if_changed_dep,rustc_library)

diff --git a/rust/exports.c b/rust/exports.c
index 3803c21d1403..1b870e8e83ea 100644
--- a/rust/exports.c
+++ b/rust/exports.c
@@ -16,7 +16,6 @@
#define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym)

#include "exports_core_generated.h"
-#include "exports_alloc_generated.h"
#include "exports_bindings_generated.h"
#include "exports_kernel_generated.h"

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 243d8c49a57b..b1580534947d 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -2,8 +2,8 @@

//! Allocator support.

-use super::{flags::*, Flags};
-use core::alloc::{GlobalAlloc, Layout};
+use super::Flags;
+use core::alloc::Layout;
use core::ptr;
use core::ptr::NonNull;

@@ -40,23 +40,6 @@ fn aligned_size(new_layout: Layout) -> usize {
layout.size()
}

-/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
-///
-/// # Safety
-///
-/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
-/// - `new_layout` must have a non-zero size.
-pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
- let size = aligned_size(new_layout);
-
- // SAFETY:
- // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
- // function safety requirement.
- // - `size` is greater than 0 since it's from `layout.size()` (which cannot be zero according
- // to the function safety requirement)
- unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 }
-}
-
/// # Invariants
///
/// One of the following `krealloc`, `vrealloc`, `kvrealloc`.
@@ -116,41 +99,6 @@ unsafe fn realloc(
}
}

-unsafe impl GlobalAlloc for Kmalloc {
- unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
- // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
- // requirement.
- unsafe { krealloc_aligned(ptr::null_mut(), layout, GFP_KERNEL) }
- }
-
- unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
- unsafe {
- bindings::kfree(ptr as *const core::ffi::c_void);
- }
- }
-
- unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
- // SAFETY:
- // - `new_size`, when rounded up to the nearest multiple of `layout.align()`, will not
- // overflow `isize` by the function safety requirement.
- // - `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
- let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
-
- // SAFETY:
- // - `ptr` is either null or a pointer allocated by this allocator by the function safety
- // requirement.
- // - the size of `layout` is not zero because `new_size` is not zero by the function safety
- // requirement.
- unsafe { krealloc_aligned(ptr, layout, GFP_KERNEL) }
- }
-
- unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
- // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
- // requirement.
- unsafe { krealloc_aligned(ptr::null_mut(), layout, GFP_KERNEL | __GFP_ZERO) }
- }
-}
-
unsafe impl Allocator for Vmalloc {
unsafe fn realloc(
ptr: Option<NonNull<u8>>,
@@ -187,9 +135,6 @@ unsafe fn realloc(
}
}

-#[global_allocator]
-static ALLOCATOR: Kmalloc = Kmalloc;
-
// See <https://github.com/rust-lang/rust/pull/86844>.
#[no_mangle]
static __rust_no_alloc_shim_is_unstable: u8 = 0;
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index efacca63c897..7e7b6b3d5bb9 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
-
# `--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) \
-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 f270c7b0cf34..3421a9ea3604 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,
)

--
2.45.2