Hi,
On 08/17/2018 09:19 AM, Jan Kiszka wrote:
> Hi Ralf,
>
> this seems to work, despite the comment. Do you remember why we have
> that restriction?
>
> diff --git a/hypervisor/include/jailhouse/header.h
> b/hypervisor/include/jailhouse/header.h
> index 518bc5cb..9dc76f81 100644
> --- a/hypervisor/include/jailhouse/header.h
> +++ b/hypervisor/include/jailhouse/header.h
> @@ -43,7 +43,7 @@ struct jailhouse_virt_console {
> unsigned int tail;
> /* current implementation requires the size of the content to be a
> * power of two */
> - char content[2048];
> + char content[4096 - 2 * sizeof(unsigned int)];
That's been a while… I remember that there have been some arguments, but
it's in deed not obvious by looking at the code…
[grabs out an old review of a previous revision]
Here's the rationale: [1]
Writer side increments the tail pointer without modulo operations
(hv/printk.c:41). If it's not a power of two, it will fail as we get
misaligned once we overflow the unsigned int. AFAICT, on reader side
we're relying on that alignement (main.c:281).
This issue should become visible, once the tail pointer overflows 32
bit. You could test this situation by offsetting the initialisation of
head/tail.
Ralf
[1] <[email protected]>
https://groups.google.com/forum/#!topic/jailhouse-dev/LFBpnSaAFhU
> };
>
> /**
>
> Jan
>
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