x86/audit: Fix -Wmissing-variable-declarations warning for ia32_xyz_class

When building x86 defconfig with Clang-18 I get the following warnings:

  | arch/x86/ia32/audit.c:6:10: warning: no previous extern declaration for non-static variable 'ia32_dir_class' [-Wmissing-variable-declarations]
  |     6 | unsigned ia32_dir_class[] = {
  | arch/x86/ia32/audit.c:11:10: warning: no previous extern declaration for non-static variable 'ia32_chattr_class' [-Wmissing-variable-declarations]
  |    11 | unsigned ia32_chattr_class[] = {
  | arch/x86/ia32/audit.c:16:10: warning: no previous extern declaration for non-static variable 'ia32_write_class' [-Wmissing-variable-declarations]
  |    16 | unsigned ia32_write_class[] = {
  | arch/x86/ia32/audit.c:21:10: warning: no previous extern declaration for non-static variable 'ia32_read_class' [-Wmissing-variable-declarations]
  |    21 | unsigned ia32_read_class[] = {
  | arch/x86/ia32/audit.c:26:10: warning: no previous extern declaration for non-static variable 'ia32_signal_class' [-Wmissing-variable-declarations]
  |    26 | unsigned ia32_signal_class[] = {

These warnings occur due to their respective extern declarations being
scoped inside of audit_classes_init as well as only being enabled with
`CONFIG_IA32_EMULATION=y`:

  | static int __init audit_classes_init(void)
  | {
  | #ifdef CONFIG_IA32_EMULATION
  |	extern __u32 ia32_dir_class[];
  |	extern __u32 ia32_write_class[];
  |	extern __u32 ia32_read_class[];
  |	extern __u32 ia32_chattr_class[];
  |	audit_register_class(AUDIT_CLASS_WRITE_32, ia32_write_class);
  |	audit_register_class(AUDIT_CLASS_READ_32, ia32_read_class);
  |	audit_register_class(AUDIT_CLASS_DIR_WRITE_32, ia32_dir_class);
  |	audit_register_class(AUDIT_CLASS_CHATTR_32, ia32_chattr_class);
  | #endif
  |	audit_register_class(AUDIT_CLASS_WRITE, write_class);
  |	audit_register_class(AUDIT_CLASS_READ, read_class);
  |	audit_register_class(AUDIT_CLASS_DIR_WRITE, dir_class);
  |	audit_register_class(AUDIT_CLASS_CHATTR, chattr_class);
  |	return 0;
  | }

Lift the extern declarations to their own header and resolve scoping
issues (and thus fix the warnings).

Moreover, change __u32 to unsigned so that we match the definitions:

  | unsigned ia32_dir_class[] = {
  | #include <asm-generic/audit_dir_write.h>
  | ~0U
  | };
  |
  | unsigned ia32_chattr_class[] = {
  | #include <asm-generic/audit_change_attr.h>
  | ~0U
  | };
  | ...

This patch is similar to commit:

  0e5e3d4 ("x86/audit: Fix a -Wmissing-prototypes warning for ia32_classify_syscall()") [1]

Signed-off-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/all/20200516123816.2680-1-b.thiel@posteo.de/ [1]
Link: ClangBuiltLinux#1920
Link: https://lore.kernel.org/r/20230829-missingvardecl-audit-v1-1-34efeb7f3539@google.com

Author: JustinStitt

arch/x86/include/asm/audit.h

@@ -4,4 +4,11 @@
 
 int ia32_classify_syscall(unsigned int syscall);
 
+extern unsigned ia32_dir_class[];
+extern unsigned ia32_write_class[];
+extern unsigned ia32_read_class[];
+extern unsigned ia32_chattr_class[];
+extern unsigned ia32_signal_class[];
+
+
 #endif /* _ASM_X86_AUDIT_H */

arch/x86/kernel/audit_64.c

@@ -63,11 +63,6 @@ int audit_classify_syscall(int abi, unsigned syscall)
 static int __init audit_classes_init(void)
 {
 #ifdef CONFIG_IA32_EMULATION
-	extern __u32 ia32_dir_class[];
-	extern __u32 ia32_write_class[];
-	extern __u32 ia32_read_class[];
-	extern __u32 ia32_chattr_class[];
-	extern __u32 ia32_signal_class[];
 	audit_register_class(AUDIT_CLASS_WRITE_32, ia32_write_class);
 	audit_register_class(AUDIT_CLASS_READ_32, ia32_read_class);
 	audit_register_class(AUDIT_CLASS_DIR_WRITE_32, ia32_dir_class);