rust: Proper bindgen sources for BTF debug builds

As Clang 14 supports the btf_type_tag attribute and building with
PAHOLE_HAS_BTF_TAG defines BTF_TYPE_TAG(value) to be
__attribute__((btf_type_tag(#value))). Because of this bindgen might get
confused and discards constness of attributed function parameters that
are indeed const pointers (like const char __user * -> char *).

This patch fixes that by passing a BINDGEN_RUN definition to bindgen
that causes BTF_TYPE_TAG(value) to be defined as nothing, thus
generating proper definitions for functions like write in the
file_operations struct.

Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>

include/linux/compiler_types.h

@@ -5,7 +5,7 @@
 #ifndef __ASSEMBLY__
 
 #if defined(CONFIG_DEBUG_INFO_BTF) && defined(CONFIG_PAHOLE_HAS_BTF_TAG) && \
-	__has_attribute(btf_type_tag)
+	__has_attribute(btf_type_tag) && !defined(__BINDGEN__)
 # define BTF_TYPE_TAG(value) __attribute__((btf_type_tag(#value)))
 #else
 # define BTF_TYPE_TAG(value) /* nothing */

rust/Makefile

@@ -297,7 +297,7 @@ else
 bindgen_c_flags_lto = $(bindgen_c_flags)
 endif
 
-bindgen_c_flags_final = $(bindgen_c_flags_lto)
+bindgen_c_flags_final = $(bindgen_c_flags_lto) -D__BINDGEN__
 
 quiet_cmd_bindgen = BINDGEN $@
       cmd_bindgen = \