Re: [Minios-devel] [UNIKRAFT PATCH 4/8] plat/xen: Align x86 interrupt stack address at compile time

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

Hi Costin,

just one remark:

On 4/23/19 12:41 PM, Costin Lupu wrote:
> This patch aligns the stack base address at compile time and makes the
> irqstack variable public.
>
> Signed-off-by: Costin Lupu <costin.lupu@xxxxxxxxx>
> ---
>   plat/xen/x86/arch_events.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/plat/xen/x86/arch_events.c b/plat/xen/x86/arch_events.c
> index 1e165c81..7d7289fc 100644
> --- a/plat/xen/x86/arch_events.c
> +++ b/plat/xen/x86/arch_events.c
> @@ -30,9 +30,10 @@
>   #include <stdint.h>
>   #include <x86/cpu.h>
>   #include <uk/plat/config.h>
> +#include <uk/essentials.h>
>   
>   #if defined(__x86_64__)
> -static char irqstack[2 * STACK_SIZE];
> +char irqstack[STACK_SIZE] __align(STACK_SIZE);
>   
>   static struct pda {
>         int irqcount;       /* offset 0 (used in x86_64.S) */
> @@ -48,8 +49,7 @@ void arch_init_events(void)
>         wrmsrl(0xc0000101, (uint64_t) &cpu0_pda);
>         cpu0_pda.irqcount = -1;
>         cpu0_pda.irqstackptr =
> -                       (void *) (((unsigned long)irqstack + 2 * STACK_SIZE)
> -                       & STACK_MASK_TOP);
> +                       (void *) ((unsigned long) irqstack + STACK_SIZE);
So my understanding is that the way the code was originally set up, it 
basically wastes a bunch of memory at the top, just to guarantee alignment?
I like the patch, but I think it would benefit from an explanation in 
the patch note why going from 2*STACK_SIZE to STACK_SIZE is not an issue.
Cheers,
Florian



>   #endif
>   }
>   
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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