enable -Wmissing-variable-declarations for W=1

[nickdesaulniers]

I had sent a patch for this, but didn't have time to follow through due to the srso patch set causing a fair amount of breakage for us that week.

https://lore.kernel.org/llvm/20230807-missing_proto-v2-1-3ae2e188bb0c@google.com/

We should work through cleaning up some of the observed issues first before resending the above.

[JustinStitt]

A good amount of these are caused by variables with register storage.

llvm/llvm-project#64509 should solve some of these warnings with Clang, right?

[JustinStitt]

Can someone help me understand what to do in order to fix some of these warnings?

Here's a case I found from an x86/defconfig build:

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[] = {

so it says "no previous extern declaration" so it seems the fix would be to add static and call it a day? right?

arch/x86/ia32/audit.c:6:17: warning: unused variable 'ia32_dir_class' [-Wunused-variable]
    6 | static unsigned ia32_dir_class[] = {
      |                 ^~~~~~~~~~~~~~

Well now we get an unused variable warning and it seems there is an extern:

$ grep "ia32_dir_class"

...
arch/x86/kernel/audit_64.c
66:     extern __u32 ia32_dir_class[];
73:     audit_register_class(AUDIT_CLASS_DIR_WRITE_32, ia32_dir_class);
...

So what am I to make of this? Is the warning wrong? Is there a different solution that I should be going for here?

I wonder if it's caused by the differing types __u32 vs unsigned.

cc @nathanchance

edit: Ah, it looks like CONFIG_IA32_EMULATION=y is required to expose the extern.

[nathanchance]

It seems like in that case, the declarations in arch/x86/kernel/audit_64.c should be hoisted into a header file (perhaps arch/x86/include/asm/audit.h?) that is included in both arch/x86/kernel/audit_64.c and arch/x86/ia32/audit.c. It also seems like the type of ia32_dir_class should be changed from unsigned to __u32?

[JustinStitt]

@nathanchance should they be hiding:

#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);
	audit_register_class(AUDIT_CLASS_CHATTR_32, ia32_chattr_class);
	audit_register_class(AUDIT_CLASS_SIGNAL_32, ia32_signal_class);
#endif

behind this config or have this in a header like you said (without the ifdef)

[nathanchance]

I don't think the declarations need to be put under an #ifdef in the header file, if that is what you are asking?

[JustinStitt]

I don't think the declarations need to be put under an #ifdef in the header file, if that is what you are asking?

Yeah, that's what I'm wodering. Why are they in the ifdef at all. I'll test moving them out.