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..
