Jeremy Fitzhardinge wrote:
> Single entry pros:
>
> * simpler control flow?
>
Simpler to maintain the code. Maintaining multiple intertwined entry
points is a mess. It used to be done for Visual workstation, and the
code got merged back together. Here's a pretty easy thing to do:
ENTRY(startup_32)
#ifdef CONFIG_PARAVIRT
movl %cs, %eax
testl $0x3, %eax
jnz pv_startup_32
#endif
Now you don't need any special magic at all to register an alternate
entry point.
> cons:
>
> * requires "hypervisor sniffing" to work out what hypervisor we're under
> o mandates setting %ebx to a magic constant?
> * not possible to have hypervisor-specific setup before setting up
> stacks, making calls, etc
>
>
> Where do the ebx constants come from anyway? If they're provided by the
> hypervisor itself, it means we need to have a registry of who's using
> what number, right? We'd require them to all be unique (since
> collisions would be disastrous), and also they need to be densely
> allocated (single we're using them as an array index).
>
Why is registering these constants hard? I prefer the symmetry of
having all vendors use the same entry method rather than encouraging
ad-hoc hacks.
Zach
