rust: kbuild: fix export of bss symbols

Symbols in the bss segment are not currently exported. This is a problem
for Rust modules that link against statics, that are resident in the kernel
image. Thus export symbols in the bss segment.

Fixes: 2f7ab12 ("Kbuild: add Rust support")
Signed-off-by: Andreas Hindborg <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Tested-by: Alice Ryhl <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Reworded slightly. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: metaspace

rust/Makefile

@@ -305,7 +305,7 @@ $(obj)/bindings/bindings_helpers_generated.rs: $(src)/helpers.c FORCE
 quiet_cmd_exports = EXPORTS $@
       cmd_exports = \
 	$(NM) -p --defined-only $< \
-		| awk '/ (T|R|D) / {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
+		| awk '/ (T|R|D|B) / {printf "EXPORT_SYMBOL_RUST_GPL(%s);\n",$$3}' > $@
 
 $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
 	$(call if_changed,exports)