Re: [Minios-devel] [UNIKRAFT PATCHv5 17/46] plat/kvm: Add linker script for Arm64

["Wei Chen (Arm Technology China)" <Wei.Chen@xxxxxxx>]

Hi Simon,

> -----Original Message-----
> From: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
> Sent: 2018年9月11日 17:26
> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; Julien Grall
> <Julien.Grall@xxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [Minios-devel] [UNIKRAFT PATCHv5 17/46] plat/kvm: Add linker
> script for Arm64
> 
> On 11.09.2018 07:26, Wei Chen (Arm Technology China) wrote:
> > Hi Julien,
> >
> >> -----Original Message-----
> >> From: Julien Grall <julien.grall@xxxxxxx>
> >> Sent: 2018年9月10日 18:16
> >> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> >> devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> >> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> >> Subject: Re: [Minios-devel] [UNIKRAFT PATCHv5 17/46] plat/kvm: Add linker
> >> script for Arm64
> >>
> >> Hi Wei,
> >>
> >> On 10/09/18 09:31, Wei Chen (Arm Technology China) wrote:
> >>>> -----Original Message-----
> >>>> From: Julien Grall <julien.grall@xxxxxxx>
> >>>> Sent: 2018年9月7日 22:50
> >>>> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> >>>> devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> >>>> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> >>>> Subject: Re: [Minios-devel] [UNIKRAFT PATCHv5 17/46] plat/kvm: Add linker
> >>>> script for Arm64
> >>>>
> >>>> Hi,
> >>>>
> >>>> On 08/10/2018 08:08 AM, Wei Chen wrote:
> >>>>> +       /* Read-write data that is not initialized explicitly in code */
> >>>>> +       .bss :
> >>>>> +       {
> >>>>> +               *(.bss)
> >>>>> +               *(.bss.*)
> >>>>> +               *(COMMON)
> >>>>> +               . = ALIGN(__PAGE_SIZE);
> >>>>
> >>>> If you define the stack and page-table here. You can then free once boot
> >>>> is done.
> >>>
> >>> I had thought a similar method before, but I am afraid to increase the
> >>> image size, so I didn't use this method. Maybe I was considering too much
> >>> for it?
> >>
> >> IHMO trying to reduce the image size in early stage of the arm64 support
> >> is very aggressive. This should be looked once you are done with the
> >> core support.
> >>
> >> But I am not entirely sure to understand the concern regarding the image
> >> size. As this is part of BSS, the actual binary will not be bigger in
> >> the disk.
> >>
> >> In the guest memory, you will indeed use more memory. You can introduce
> >> a new variable to tell you where the "boot memory". So you can discard
> >> it easily once you are done with it.
> >>
> >
> > Ok, I will try it : )
> 
> Hey,
> 
> it is fine to me, to do such optimizations with follow-up patches.
> Some TODO comments in the code should indicate that there is room for
> improvements wherever we can foresee it already during development.
> So, I would document for now that the boot stack could be claimed back
> later during boot. I actually think we should find a generic solution
> with a ukplat interface since claiming back the boot stack could be
> possible also on other platforms. For some Unikernels it even may make
> sense to keep using the boot stack for the whole lifetime (e.g., no need
> for a scheduler), for others it makes sense. So the decision of claiming
> back the memory should come from a higher level.
> 

That would be better, I will add the TODO comments.

> >
> >> This is not a proper "init section" but a way to avoid rely on free
> >> space after the image in memory.
> >>
> >> Cheers,
> >>
> >> --
> >> Julien Grall
> 
> Cheers,
> 
> Simon
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