Re: [Qemu-devel] [PATCH v1 2/4] target-arm: A64: Handle blr lr

[Alex Bennée]

Edgar E. Iglesias <address@hidden> writes:

> On Thu, May 01, 2014 at 10:31:06AM +0100, Peter Maydell wrote:
>> On 1 May 2014 10:02, Alex Bennée <address@hidden> wrote:
>> >
>> > Edgar E. Iglesias <address@hidden> writes:
>> >
>> >> From: "Edgar E. Iglesias" <address@hidden>
>> >>
>> >> For linked branches, updates to the link register happen
>> >> conceptually after the read of the branch target register.
>> >>
>> >> Signed-off-by: Edgar E. Iglesias <address@hidden>
>> >
>> > I'm trying to think of a case where this could actually cause a problem
>> > but I can't. However from a clarity/correctness point of view it's
>> > better.
>> 
>> Well, we actually misexecute "BLR LR" otherwise, right?
>> That's probably not very common but there's no reason it
>> might not occur (eg call to a function pointer from a
>> function where LR has been saved on entry and is free
>> for use as a generic tempreg).
>
> Right. For example, the kernel/kvm actually does this in
> arch/arm64/kvm/hyp.S:773:       blr     lr

Of course, I see know ;-)

-- 
Alex Bennée