Re: [Minios-devel] [PATCH v3 19/43] arm64: add shared_info support

[Huang Shijie <shijie.huang@xxxxxxx>]

On Mon, Apr 23, 2018 at 12:05:51PM +0100, Julien Grall wrote:
> Hi Shijie,
> 
> On 23/04/18 09:49, Huang Shijie wrote:
> >On Wed, Apr 18, 2018 at 09:34:18PM +0100, Julien Grall wrote:
> >>Hi,
> >>
> >>On 16/04/2018 07:31, Huang Shijie wrote:
> >>>Add the shared_info page.
> >>>
> >>>Signed-off-by: Huang Shijie <shijie.huang@xxxxxxx>
> >>>---
> >>>  arch/arm/arm64/arm64.S | 3 +++
> >>>  1 file changed, 3 insertions(+)
> >>>
> >>>diff --git a/arch/arm/arm64/arm64.S b/arch/arm/arm64/arm64.S
> >>>index 9eb7ea0..fa3406f 100644
> >>>--- a/arch/arm/arm64/arm64.S
> >>>+++ b/arch/arm/arm64/arm64.S
> >>>@@ -25,6 +25,7 @@
> >>>      .globl boot_l2_pgtable
> >>>      .globl idmap_l0_pgtable
> >>>      .globl idmap_l1_pgtable
> >>>+    .globl shared_info
> >>>      .align 12
> >>>  boot_l0_pgtable:
> >>>@@ -37,6 +38,8 @@ idmap_l0_pgtable:
> >>>      .fill  PAGE_SIZE,1,0
> >>>  idmap_l1_pgtable:
> >>>      .fill  PAGE_SIZE,1,0
> >>>+shared_info:
> >>>+    .fill  PAGE_SIZE,1,0
> >>
> >>Why does it have to be defined in assembly? Can't this be done in C? Or even
> >I think we'd better keep it here.
> 
> Assembly should really only be used when this is strictly necessary...
> 
> >We used the shared_info at arch_init() which the memory system is not ready 
> >yet.
> 
> ... if it is used in arch_init() then it should be defined in C statically.
I found it is hard to code it in C.

The following is what I did:

  ----------------------------------------------------------
  shared_info_t shared_info __attribute__((aligned(PAGE_SIZE)));
  ----------------------------------------------------------

But we need the shared_info to occupy a whole page which is
used in map_shared_info().

Is there a good way to solve it?

Thanks
Huang Shijie

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