On Sat, 26 Mar 2022, Elliott Mitchell wrote: > The hypercalls implementation for Linux and FreeBSD have two key headers, > hypercall.h and hypervisor.h. I'm curious why the implementations for > x86 and ARM* are so distinct. > > I found it fairly straightforward to implement ARM* versions of the x86 > _hypercall#() macros. Once that is done, most of the wrappers in the x86 > hypercall.h can be moved to a shared hypervisor.h header. > > Why does Xen/ARM on Linux still have hypercall.S when merging the > headers should reduce maintainance? > > Was GCC extended inline assembly language for ARM* thought too awful? > > I'm also curious why these headers are part of the Linux kernel, instead > of being maintained by the Xen Project?
I would have to dig through ancient archives to give you a full answer but the reason was that the asm inline on ARM didn't provide enough guarantees on ordering and registers it would use and clobber.
