Re: [Xen-devel] [PATCH v6 08/15] x86/efi: create new early memory allocator

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.09.16 at 11:45, <daniel.kiper@xxxxxxxxxx> wrote:
> On Mon, Sep 19, 2016 at 09:17:50AM -0600, Jan Beulich wrote:
>> >>> On 19.09.16 at 17:04, <daniel.kiper@xxxxxxxxxx> wrote:
>> > On Mon, Sep 19, 2016 at 06:12:35AM -0600, Jan Beulich wrote:
>> >> >>> On 12.09.16 at 22:18, <daniel.kiper@xxxxxxxxxx> wrote:
>> >> > --- a/xen/arch/x86/setup.c
>> >> > +++ b/xen/arch/x86/setup.c
>> >> > @@ -520,6 +520,8 @@ static void noinline init_done(void)
>> >> >
>> >> >      system_state = SYS_STATE_active;
>> >> >
>> >> > +    free_ebmalloc_unused_mem();
>> >>
>> >> Now that the allocator properly lives in common code, this appears
>> >> to lack an ARM side counterpart.
>> >
>> > Why? It is called only from xen/arch/x86/setup.c:__start_xen() and all
>> > ebmalloc stuff is in #ifndef CONFIG_ARM. So, free_ebmalloc_unused_mem()
>> > will be needed only if we add ARM support here.
>>
>> Well, it being inside that conditional is part of the problem - there's
>> no apparent point for all of it to be.
> 
> I can agree that this is potentially generic stuff (well, I understand that
> it is our final goal but unreachable yet due to various things). However,
> right know it is only used on x86. So, I am not sure what is the problem
> with #ifndef CONFIG_ARM right now...

It is a fact that these should actually not be there, so we ought to
at least limit them to the smallest possible count and scopes.

>> Arguably the one static function may better be, as other workarounds
>> to avoid the "unused" compiler warning wouldn't be any better.
> 
> Do you mean static function with empty body for ARM? It is not needed
> right now because it is never called on ARM. Am I missing something?

You misunderstood - I said that for this one (unused) static
function such an #ifdef is probably okay, as the presumably
smallest possible workaround.

>> >> > +static unsigned long __initdata ebmalloc_allocated;
>> >> > +
>> >> > +/* EFI boot allocator. */
>> >> > +static void __init *ebmalloc(size_t size)
>> >> > +{
>> >> > +    void *ptr = ebmalloc_mem + ebmalloc_allocated;
>> >> > +
>> >> > +    ebmalloc_allocated += (size + sizeof(void *) - 1) & 
>> >> > ~((typeof(size))sizeof(void *) - 1);
>> >>
>> >> What's the point of this ugly cast?
>> >
>> > In general ALIGN_UP() would be nice here. However, there is no such thing
>> > in Xen headers (or I cannot find it). Should I add one? As separate patch?
>>
>> I understand what you want the expression for, but you didn't
>> answer my question. Or do you not realize that all this cast is
>> about is a strange way of converting an expression of type
>> size_t to type size_t?
> 
> Does sizeof() returns size_t type? I was thinking that it returns
> a number calculated during compilation, however, it does not have
> specific type.

Every expression needs to have a well specified type. Even
plain numbers do.

Jan


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