rust: rework & improve robustness of is_rust_module.sh

This also simplifies the file and makes it work under any POSIX shell.

Link: #657
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/macros/module.rs

@@ -503,6 +503,15 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
             /// Used by the printing macros, e.g. [`info!`].
             const __LOG_PREFIX: &[u8] = b\"{name}\\0\";
 
+            /// The \"Rust loadable module\" mark, for `scripts/is_rust_module.sh`.
+            //
+            // This may be best done another way later on, e.g. as a new modinfo
+            // key or a new section. For the moment, keep it simple.
+            #[cfg(MODULE)]
+            #[doc(hidden)]
+            #[used]
+            static __IS_RUST_MODULE: () = ();
+
             static mut __MOD: Option<{type_}> = None;
 
             // SAFETY: `__this_module` is constructed by the kernel at load time and will not be freed until the module is unloaded.

scripts/is_rust_module.sh

@@ -1,19 +1,13 @@
-#!/bin/bash
+#!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
 #
-# is_rust_module.sh MOD.ko
+# is_rust_module.sh module.ko
 #
-# Returns 0 if MOD.ko is a rust module, 1 otherwise.
+# Returns `0` if `module.ko` is a Rust module, `1` otherwise.
 
 set -e
-module="$*"
 
-while IFS= read -r line
-do
-  # Any symbol beginning with "_R" is a v0 mangled rust symbol
-  if [[ $line =~ ^[0-9a-fA-F]+[[:space:]]+[uUtTrR][[:space:]]+_R[^[:space:]]+$ ]]; then
-    exit 0
-  fi
-done < <(${NM} "$module")
-
-exit 1
+# Using the `16_` prefix ensures other symbols with the same substring
+# are not picked up (even if it would be unlikely). The last part is
+# used just in case LLVM decides to use the `.` suffix.
+${NM} "$*" | grep -qE '^[0-9a-fA-F]+ r _R[^[:space:]]+16___IS_RUST_MODULE[^[:space:]]*$'