Implement link-time panic and assertion

Signed-off-by: Gary Guo <[email protected]>

Author: nbdd0121

rust/Makefile

@@ -32,6 +32,7 @@ rustdoc-compiler_builtins: $(srctree)/rust/compiler_builtins.rs FORCE
 	$(call if_changed,rustdoc)
 
 rustdoc-kernel: private rustdoc_target_flags = --extern alloc \
+    --extern link_time_panic \
     --extern module=$(objtree)/rust/libmodule.so
 rustdoc-kernel: $(srctree)/rust/kernel/lib.rs rustdoc-module \
     $(objtree)/rust/libmodule.so $(objtree)/rust/bindings_generated.rs FORCE
@@ -147,9 +148,17 @@ $(objtree)/rust/alloc.o: $$(RUST_LIB_SRC)/alloc/src/lib.rs \
     $(objtree)/rust/compiler_builtins.o FORCE
 	$(call if_changed_dep,rustc_library)
 
+# link_time_panic.o is deliberately only compiled as a dependency but not
+# included in obj-y.
+$(objtree)/rust/link_time_panic.o: $(srctree)/rust/link_time_panic.rs \
+    $(objtree)/rust/compiler_builtins.o FORCE
+	$(call if_changed_dep,rustc_library)
+
 # ICE on `--extern module`: https://github.com/rust-lang/rust/issues/56935
 $(objtree)/rust/kernel.o: private rustc_target_flags = --extern alloc \
+    --extern link_time_panic \
     --extern module=$(objtree)/rust/libmodule.so
 $(objtree)/rust/kernel.o: $(srctree)/rust/kernel/lib.rs $(objtree)/rust/alloc.o \
+    $(objtree)/rust/link_time_panic.o \
     $(objtree)/rust/libmodule.so $(objtree)/rust/bindings_generated.rs FORCE
 	$(call if_changed_dep,rustc_library)

rust/link_time_panic.rs

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Link-time panicking.
+//!
+//! In Rust it is very common to use assertions extensively and defensively.
+//! Sometimes we know a condition could be checked statically, but it could not
+//! be enforced in Rust (e.g. perform some checks in const functions, but those
+//! functions could still be called in the runtime).
+//!
+//! This crate provides a method `link_time_panic`, which will panic in
+//! compile-time if executed in const context, and will trigger a link error
+//! if not executed in compile time and optimizer does not optimise away the
+//! call.
+
+#![no_std]
+#![feature(const_panic, core_panic)]
+
+/// Panics if executed in const context, or triggers a link error if not.
+#[inline(never)]
+#[no_mangle]
+pub const fn link_time_panic(msg: &'static str) {
+    // Could also be panic!(msg) to avoid using unstable feature `core_panic`,
+    // but it is not allowed in Rust 2021, while panic!("{}", msg) could not
+    // yet be used in const context.
+    core::panicking::panic(msg);
+}
+
+/// Asserts that a boolean expression is `true` at compile time.
+///
+/// This will invoke the [`link_time_panic`] function if the compiler or optimizer
+/// cannot guarantee the condition will be evaluated to `true`.
+#[macro_export]
+macro_rules! link_time_assert {
+    ($cond:expr $(,)?) => {{
+        if !$cond {
+            $crate::link_time_panic(concat!("assertion failed: ", stringify!($cond)));
+        }
+    }};
+    ($cond:expr, $msg:expr) => {{
+        if !$cond {
+            $crate::link_time_panic($msg);
+        }
+    }};
+}

scripts/generate_rust_analyzer.py

@@ -71,11 +71,19 @@ def append_crate(display_name, root_module, is_workspace_member, deps, cfg):
     )
     crates[-1]["proc_macro_dylib_path"] = "rust/libmodule.so"
 
+    append_crate(
+        "link_time_panic",
+        srctree / "rust" / "link_time_panic.rs",
+        True,
+        ["core", "compiler_builtins"],
+        [],
+    )
+
     append_crate(
         "kernel",
         srctree / "rust" / "kernel" / "lib.rs",
         True,
-        ["core", "alloc", "module"],
+        ["core", "alloc", "module", "link_time_panic"],
         cfg,
     )
     crates[-1]["env"]["RUST_BINDINGS_FILE"] = str(bindings_file.resolve(True))