Messages in this thread |  | | Date | Wed, 30 Sep 2020 19:13:46 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 04/17] x86/acrn: Introduce hypercall interfaces |
| |
On Wed, Sep 30, 2020 at 11:10:36AM -0500, Segher Boessenkool wrote:
> Since this variable is a local register asm, on entry to the asm the > compiler guarantees that the value lives in the assigned register (the > "r8" hardware register in this case). This all works completely fine. > This is the only guaranteed behaviour for local register asm (well, > together with analogous behaviour for outputs).
Right, that's what they're trying to achieve. The hypervisor calling convention needs that variable in %r8 (which is somewhat unfortunate).
AFAIK this is the first such use in the kernel, but at least the gcc-4.9 (our oldest supported version) claims to support this.
So now we need to know if clang will actually do this too..
|  |