Re: [Xen-devel] [PATCH] xen/arm64: Don't zero BSS when booting using EFI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.02.17 at 15:24, <julien.grall@xxxxxxx> wrote:
> On 03/02/17 07:41, Jan Beulich wrote:
>>>>> On 02.02.17 at 20:25, <julien.grall@xxxxxxx> wrote:
>>> @@ -261,6 +265,8 @@ GLOBAL(init_secondary)
>>>          sub   x20, x19, x0           /* x20 := phys-offset */
>>>
>>>          mov   x22, #1                /* x22 := is_secondary_cpu */
>>> +        /* Skip zero BSS on secondary CPUs to avoid nasty surprises. */
>>> +        mov   x26, #1                /* X26 := skip_zero_bss */
>>>
>>>  common_start:
>>>          mov   x24, #0                /* x24 := CPU ID. Initialy zero until 
>>> we
>>> @@ -314,8 +320,8 @@ common_start:
>>>
>>>  el2:    PRINT("- Xen starting at EL2 -\r\n")
>>>
>>> -        /* Zero BSS On the boot CPU to avoid nasty surprises */
>>> -        cbnz  x22, skip_bss
>>> +        /* Zero BSS only when requested to avoid nasty surprises. */
>>> +        cbnz  x26, skip_bss
>>
>> Comparing the original comment here with both this and the
>> earlier hunk, I think the intended meaning is lost. Zeroing the
>> BSS on secondary CPUs is certainly a bug, not a nasty surprise.
>> What I think the original comment is meaning to say is "the
>> BSS should have been zeroed already, but let's better not rely
>> on that".
> 
> This is not the original meaning.

Are you sure the comment wasn't just copied from x86 code?

> On non-EFI setup BSS will not be 
> zeroed before hand as the loader of Xen does not know the size of BSS.

So I would recommend correcting the comments at once to reflect
what they are now supposed to mean.

Jan


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