kbuild: rust: remove the `alloc` crate and `GlobalAlloc`

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>

3 files changed, 12 insertions, 97 deletions

diff --git a/rust/Makefile b/rust/Makefile
index 0856fd6bc610..3678e79317f1 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -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
@@ -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)) \
@@ -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 \
@@ -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)
 
@@ -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 \
@@ -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 \
@@ -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
@@ -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
@@ -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)
 
@@ -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)
 
diff --git a/rust/exports.c b/rust/exports.c
index e5695f3b45b7..82a037381798 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_helpers_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 f8a1f0feb25d..a041bbfdabec 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -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;
 
@@ -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`.
@@ -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,
@@ -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;