Re: [PATCH] arm64/kernel/entry: refine comment of stack overflow check

[Guoheyi]

在 2019/12/2 20:33, Mark Rutland 写道:
> On Mon, Dec 02, 2019 at 07:37:02PM +0800, Heyi Guo wrote:
> > Stack overflow checking can be done by testing
> > sp & (1 << THREAD_SHIFT)
> > only for the stacks are aligned to (2 << THREAD_SHIFT) with size of
> > (1 << THREAD_SIZE), and this is the case when CONFIG_VMAP_STACK is
> > set.
> Good point, I was sloppy with this comment.
>
> > Fix the code comment to avoid confusion.
> >
> > Signed-off-by: Heyi Guo <guoheyi@xxxxxxxxxx>
> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Cc: Will Deacon <will@xxxxxxxxxx>
> > ---
> >   arch/arm64/kernel/entry.S | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> > index cf3bd2976e57..9e8ba507090f 100644
> > --- a/arch/arm64/kernel/entry.S
> > +++ b/arch/arm64/kernel/entry.S
> > @@ -76,7 +76,8 @@ alternative_else_nop_endif
> >   #ifdef CONFIG_VMAP_STACK
> >   	/*
> >   	 * Test whether the SP has overflowed, without corrupting a GPR.
> > -	 * Task and IRQ stacks are aligned to (1 << THREAD_SHIFT).
> > +	 * Task and IRQ stacks are aligned to (2 << THREAD_SHIFT) with size of
> > +	 * (1 << THREAD_SHIFT).
> >   	 */
> Can we make that:
>
> 	Task and IRQ stacks are aligned so that SP & (1 << THREAD_SHIFT)
> 	should always be zero.
>
> ... which I think is a bit clearer.

Sure :)

Thanks,

Heyi

> With that wording:
>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
>
> Mark.
>
> >   	add	sp, sp, x0			// sp' = sp + x0
> >   	sub	x0, sp, x0			// x0' = sp' - x0 = (sp + x0) - x0 = sp
> > --
> > 2.19.1
> .