rust: bindgen: upgrade to 0.65.1

* Rationale:

Upgrades bindgen to code-generation for anonymous unions, structs, and enums [7]
for LLVM-16 based toolchains.

The following upgrade also incorporates `noreturn` support from bindgen
allowing us to remove useless `loop` calls which was placed as a
workaround.

* Truncated build logs on using bindgen `v0.56.0` prior to LLVM-16 toolchain:

```
$ make rustdoc LLVM=1 CLIPPY=1 -j$(nproc)
  RUSTC L rust/core.o
  BINDGEN rust/bindings/bindings_generated.rs
  BINDGEN rust/bindings/bindings_helpers_generated.rs
  BINDGEN rust/uapi/uapi_generated.rs
thread 'main' panicked at '"ftrace_branch_data_union_(anonymous_at__/_/include/linux/compiler_types_h_146_2)" is not a valid Ident', .../proc-macro2-1.0.24/src/fallback.rs:693:9
...
thread 'main' panicked at '"ftrace_branch_data_union_(anonymous_at__/_/include/linux/compiler_types_h_146_2)" is not a valid Ident', .../proc-macro2-1.0.24/src/fallback.rs:693:9
...
```

* LLVM-16 Changes:

API changes [1] were introduced such that libclang would emit names like
"(unnamed union at compiler_types.h:146:2)" for unnamed unions, structs, and
enums whereas it previously returned an empty string.

* Bindgen Changes:

Bindgen `v0.56.0` on LLVM-16 based toolchains hence was unable to process the
anonymous union in `include/linux/compiler_types` `struct ftrace_branch_data`
and caused subsequent panics as the new `libclang` API emitted name was not
being handled. The following issue was fixed in Bindgen `v0.62.0` [2].

Bindgen `v0.58.0` changed the flags `--whitelist-*` and `--blacklist-*`
to `--allowlist-*` and `--blocklist-*` respectively [3].

Bindgen `v0.61.0` added support for `_Noreturn`, `[[noreturn]]`, `__attribute__((noreturn))` [4],
hence the empty `loop`s used to circumvent bindgen returning `!` in place of `()`
for noreturn attributes have been removed completely.

Bindgen `v0.61.0` also changed default functionality to bind `size_t` to `usize` [5] and
added the `--no-size_t-is-usize` [5] flag to not bind `size_t` as `usize`.

Bindgen `v0.65.0` removed `--size_t-is-usize` flag [6].

Link: llvm/llvm-project@19e984e [1]
Link: rust-lang/rust-bindgen#2319 [2]
Link: rust-lang/rust-bindgen#1990 [3]
Link: rust-lang/rust-bindgen#2094 [4]
Link: rust-lang/rust-bindgen@cc78b6f [5]
Link: rust-lang/rust-bindgen#2408 [6]
Reported-by: Josh Poimboeuf <jpoimboe@kernel.org>
Closes: https://lore.kernel.org/rust-for-linux/20230606215212.r7if2gsynajugf6j@treble/
Reported-by: Aakash Sen Sharma <aakashsensharma@gmail.com>
Closes: Rust-for-Linux#1013 [7]
Signed-off-by: Aakash Sen Sharma <aakashsensharma@gmail.com>
Link: https://lore.kernel.org/r/20230612194311.24826-1-aakashsensharma@gmail.com
[ Reword, add Josh's report and update Quick Start guide. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Documentation/process/changes.rst

@@ -32,7 +32,7 @@ you probably needn't concern yourself with pcmciautils.
 GNU C                  5.1              gcc --version
 Clang/LLVM (optional)  11.0.0           clang --version
 Rust (optional)        1.68.2           rustc --version
-bindgen (optional)     0.56.0           bindgen --version
+bindgen (optional)     0.65.1           bindgen --version
 GNU make               3.82             make --version
 bash                   4.2              bash --version
 binutils               2.25             ld -v

Documentation/rust/quick-start.rst

@@ -98,7 +98,7 @@ the ``bindgen`` tool. A particular version is required.
 
 Install it via (note that this will download and build the tool from source)::
 
-	cargo install --locked --version $(scripts/min-tool-version.sh bindgen) bindgen
+	cargo install --locked --version $(scripts/min-tool-version.sh bindgen) bindgen-cli
 
 
 Requirements: Developing

rust/Makefile

@@ -300,7 +300,7 @@ quiet_cmd_bindgen = BINDGEN $@
 	$(BINDGEN) $< $(bindgen_target_flags) \
 		--use-core --with-derive-default --ctypes-prefix core::ffi --no-layout-tests \
 		--no-debug '.*' \
-		--size_t-is-usize -o $@ -- $(bindgen_c_flags_final) -DMODULE \
+		-o $@ -- $(bindgen_c_flags_final) -DMODULE \
 		$(bindgen_target_cflags) $(bindgen_target_extra)
 
 $(obj)/bindings/bindings_generated.rs: private bindgen_target_flags = \
@@ -320,8 +320,8 @@ $(obj)/uapi/uapi_generated.rs: $(src)/uapi/uapi_helper.h \
 # given it is `libclang`; but for consistency, future Clang changes and/or
 # a potential future GCC backend for `bindgen`, we disable it too.
 $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_flags = \
-    --blacklist-type '.*' --whitelist-var '' \
-    --whitelist-function 'rust_helper_.*'
+    --blocklist-type '.*' --allowlist-var '' \
+    --allowlist-function 'rust_helper_.*'
 $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_cflags = \
     -I$(objtree)/$(obj) -Wno-missing-prototypes -Wno-missing-declarations
 $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ; \

rust/helpers.c

@@ -129,19 +129,18 @@ void rust_helper_put_task_struct(struct task_struct *t)
 EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
 
 /*
- * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
- * as the Rust `usize` type, so we can use it in contexts where Rust
- * expects a `usize` like slice (array) indices. `usize` is defined to be
- * the same as C's `uintptr_t` type (can hold any pointer) but not
- * necessarily the same as `size_t` (can hold the size of any single
+ * `bindgen` binds the C `size_t` type the Rust `usize` type, so we can
+ * use it in contexts where Rust expects a `usize` like slice (array) indices.
+ * `usize` is defined to be the same as C's `uintptr_t` type (can hold any pointer)
+ * but not necessarily the same as `size_t` (can hold the size of any single
  * object). Most modern platforms use the same concrete integer type for
  * both of them, but in case we find ourselves on a platform where
  * that's not true, fail early instead of risking ABI or
  * integer-overflow issues.
  *
  * If your platform fails this assertion, it means that you are in
- * danger of integer-overflow bugs (even if you attempt to remove
- * `--size_t-is-usize`). It may be easiest to change the kernel ABI on
+ * danger of integer-overflow bugs (even if you attempt to add
+ * `--no-size_t-is-usize`). It may be easiest to change the kernel ABI on
  * your platform such that `size_t` matches `uintptr_t` (i.e., to increase
  * `size_t`, because `uintptr_t` has to be at least as big as `size_t`).
  */

rust/kernel/lib.rs

@@ -93,7 +93,4 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
     pr_emerg!("{}\n", info);
     // SAFETY: FFI call.
     unsafe { bindings::BUG() };
-    // Bindgen currently does not recognize `__noreturn` so `BUG` returns `()`
-    // instead of `!`. See <https://github.com/rust-lang/rust-bindgen/issues/2094>.
-    loop {}
 }

scripts/min-tool-version.sh

@@ -30,7 +30,7 @@ rustc)
 	echo 1.68.2
 	;;
 bindgen)
-	echo 0.56.0
+	echo 0.65.1
 	;;
 *)
 	echo "$1: unknown tool" >&2