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kbuild: rust: remove the alloc crate and GlobalAlloc
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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>
Link: https://lore.kernel.org/r/20241004154149.93856-29-dakr@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
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Danilo Krummrich authored and ojeda committed Oct 15, 2024
1 parent 8ae740c commit 392e34b
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Showing 5 changed files with 16 additions and 108 deletions.
43 changes: 10 additions & 33 deletions rust/Makefile
Original file line number Diff line number Diff line change
Expand Up @@ -15,8 +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-$(CONFIG_RUST) += exports_alloc_generated.h exports_helpers_generated.h \
obj-$(CONFIG_RUST) += bindings.o kernel.o
always-$(CONFIG_RUST) += exports_helpers_generated.h \
exports_bindings_generated.h exports_kernel_generated.h

always-$(CONFIG_RUST) += uapi/uapi_generated.rs
Expand Down Expand Up @@ -53,11 +53,6 @@ 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)) \
Expand All @@ -81,7 +76,7 @@ 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 \
Expand All @@ -108,20 +103,11 @@ 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)

Expand Down Expand Up @@ -165,7 +151,7 @@ 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 \
Expand Down Expand Up @@ -201,7 +187,7 @@ 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 \
Expand Down Expand Up @@ -314,9 +300,6 @@ 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)

# Even though Rust kernel modules should never use the bindings directly,
# symbols from the `bindings` crate and the C helpers need to be exported
# because Rust generics and inlined functions may not get their code generated
Expand Down Expand Up @@ -363,7 +346,7 @@ 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)) \
$(rustc_sysroot) $(RUST_LIB_SRC) $(KBUILD_EXTMOD) > \
$(if $(KBUILD_EXTMOD),$(extmod_prefix),$(objtree))/rust-project.json
Expand Down Expand Up @@ -401,12 +384,6 @@ $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
$(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
+$(call if_changed_rule,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_rule,rustc_library)

$(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
+$(call if_changed_rule,rustc_library)

Expand All @@ -421,9 +398,9 @@ $(obj)/uapi.o: $(src)/uapi/lib.rs \
$(obj)/uapi/uapi_generated.rs FORCE
+$(call if_changed_rule,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_rule,rustc_library)

Expand Down
1 change: 0 additions & 1 deletion rust/exports.c
Original file line number Diff line number Diff line change
Expand Up @@ -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_helpers_generated.h"
#include "exports_bindings_generated.h"
#include "exports_kernel_generated.h"
Expand Down
65 changes: 2 additions & 63 deletions rust/kernel/alloc/allocator.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,8 @@
//!
//! Reference: <https://docs.kernel.org/core-api/memory-allocation.html>
use super::{flags::*, Flags};
use core::alloc::{GlobalAlloc, Layout};
use super::Flags;
use core::alloc::Layout;
use core::ptr;
use core::ptr::NonNull;

Expand Down Expand Up @@ -54,23 +54,6 @@ 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`.
Expand Down Expand Up @@ -156,43 +139,6 @@ unsafe impl Allocator for Kmalloc {
}
}

// SAFETY: TODO.
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) {
// SAFETY: TODO.
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) }
}
}

// SAFETY: `realloc` delegates to `ReallocFunc::call`, which guarantees that
// - memory remains valid until it is explicitly freed,
// - passing a pointer to a valid memory allocation is OK,
Expand Down Expand Up @@ -240,10 +186,3 @@ unsafe impl Allocator for KVmalloc {
unsafe { ReallocFunc::KVREALLOC.call(ptr, layout, old_layout, flags) }
}
}

#[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;
4 changes: 2 additions & 2 deletions scripts/Makefile.build
Original file line number Diff line number Diff line change
Expand Up @@ -248,7 +248,7 @@ $(obj)/%.lst: $(obj)/%.c FORCE
# Compile Rust sources (.rs)
# ---------------------------------------------------------------------------

rust_allowed_features := arbitrary_self_types,lint_reasons,new_uninit
rust_allowed_features := arbitrary_self_types,lint_reasons

# `--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
Expand All @@ -258,7 +258,7 @@ rust_common_cmd = \
-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 \
Expand Down
11 changes: 2 additions & 9 deletions scripts/generate_rust_analyzer.py
Original file line number Diff line number Diff line change
Expand Up @@ -64,13 +64,6 @@ def append_crate(display_name, root_module, deps, cfg=[], is_workspace_member=Tr
[],
)

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",
Expand All @@ -96,7 +89,7 @@ def append_crate(display_name, root_module, deps, cfg=[], is_workspace_member=Tr
append_crate(
"kernel",
srctree / "rust" / "kernel" / "lib.rs",
["core", "alloc", "macros", "build_error", "bindings"],
["core", "macros", "build_error", "bindings"],
cfg=cfg,
)
crates[-1]["source"] = {
Expand Down Expand Up @@ -133,7 +126,7 @@ def is_root_crate(build_file, target):
append_crate(
name,
path,
["core", "alloc", "kernel"],
["core", "kernel"],
cfg=cfg,
)

Expand Down

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