Re: [PATCH] cpu: microcode: replace 0 with NULL

[Jules Irenge <jbi.octave@gmail.com>]

On Tue, 26 Nov 2019, Borislav Petkov wrote:

> On Tue, Nov 26, 2019 at 12:27:34AM +0000, Jules Irenge wrote:
> > Replace 0 with NULL to fix sparse tool  warning
> >  warning: Using plain integer as NULL pointer
> > 
> > Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
> > ---
> >  arch/x86/kernel/cpu/microcode/amd.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
> > index a0e52bd00ecc..4934aa7c94e7 100644
> > --- a/arch/x86/kernel/cpu/microcode/amd.c
> > +++ b/arch/x86/kernel/cpu/microcode/amd.c
> > @@ -418,7 +418,7 @@ static int __apply_microcode_amd(struct microcode_amd *mc)
> >  static bool
> >  apply_microcode_early_amd(u32 cpuid_1_eax, void *ucode, size_t size, bool save_patch)
> >  {
> > -	struct cont_desc desc = { 0 };
> > +	struct cont_desc desc = { NULL };
> 
> So my gcc guy says that 0 and NULL are equivalent as designated
> initializers in this case. And if you look at the resulting asm, it
> doesn't change:
> 
> # arch/x86/kernel/cpu/microcode/amd.c:421: 	struct cont_desc desc = { 0 };
> 	movq	$0, 8(%rsp)	#, desc
> 	movq	$0, (%rsp)	#, desc
> 	movq	$0, 16(%rsp)	#, desc
> 	movq	$0, 24(%rsp)	#, desc
> 
> But what I'd prefer actually is, if you do them like this:
> 
> 			... = { 0,  };
> 
> because:
> 
> 1. It is clear that the memory for the struct is being cleared
> 2. The following ones - the ones after "," are missing too, on purpose,
>    because they're being cleared too.
> 
> Also pls add that explanation to the commit message.
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette
> 
Hi Boris,

Thanks for your reply and suggestion. 

I am learning patching with sparse trying to solve some problems that the 
tool complains about.

Sometime the tool is not always right. If I take your suggestion that I 
am about to do, sparse will however still complain.

so I will suggest my change to be discarded.

I will take another challenge.

Kind regards,
Jules