Test that __rust_probestack can be linked

drivers/char/rust_example_3.rs

@@ -36,6 +36,14 @@ impl KernelModule for RustExample3 {
         println!("[3] Parameters:");
         println!("[3]   my_bool:  {}", my_bool.read());
         println!("[3]   my_i32:   {}", my_i32.read());
+
+        // Including this large variable on the stack will trigger a call to 
+        // `compiler_builtins::probestack::__rust_probestack` on x86_64.
+        // This will verify that we are able to link modules which call
+        // `__rust_probestack`.
+        let x: [u64; 1028] = [5; 1028];
+        println!("Large array has length: {}", x.len());
+
         Ok(RustExample3 {
             message: "on the heap!".to_owned(),
         })

rust/Makefile

@@ -5,6 +5,7 @@ obj-$(CONFIG_RUST) += core.o compiler_builtins.o alloc.o kernel.o
 extra-$(CONFIG_RUST) += bindings_generated.rs libmodule.so
 extra-$(CONFIG_RUST) += exports_core_generated.h exports_alloc_generated.h
 extra-$(CONFIG_RUST) += exports_kernel_generated.h
+extra-$(CONFIG_RUST) += exports_compiler_builtins_generated.h
 
 ifdef CONFIG_CC_IS_CLANG
 bindgen_c_flags = $(c_flags)
@@ -62,6 +63,10 @@ $(objtree)/rust/exports_kernel_generated.h: exports_target_type := _RUST_GPL
 $(objtree)/rust/exports_kernel_generated.h: $(objtree)/rust/kernel.o FORCE
 	$(call if_changed,exports)
 
+$(objtree)/rust/exports_compiler_builtins_generated.h: exports_target_type := _RUST
+$(objtree)/rust/exports_compiler_builtins_generated.h: $(objtree)/rust/compiler_builtins.o FORCE
+	$(call if_changed,exports)
+
 quiet_cmd_rustc_procmacro = RUSTC P $@
       cmd_rustc_procmacro = \
 	$(RUSTC) $(rustc_flags) --edition 2018 --extern proc_macro \

rust/exports.c

@@ -16,3 +16,4 @@
 #include "exports_core_generated.h"
 #include "exports_alloc_generated.h"
 #include "exports_kernel_generated.h"
+#include "exports_compiler_builtins_generated.h"