The hypercall page populated with instructions by the hypervisor is not IBT

compatible due to lack of endbr64. Replace the indirect call with a new
hv_hypercall_trampoline() routine which jumps to the hypercall page without any
indirection.

Allows me to boot OpenBSD using Hyper-V on Windows 11 again.

ok guenther@

1 files changed, 2 insertions, 3 deletions

diff --git a/sys/dev/pv/hyperv.c b/sys/dev/pv/hyperv.c
index 08a713d814d..da9bf3ae6d7 100644
--- a/sys/dev/pv/hyperv.c
+++ b/sys/dev/pv/hyperv.c
@@ -407,9 +407,8 @@ hv_hypercall(struct hv_softc *sc, uint64_t control, void *input,
 	}
 
 #ifdef __amd64__
-	__asm__ volatile ("mov %0, %%r8" : : "r" (output_pa) : "r8");
-	__asm__ volatile ("call *%3" : "=a" (status) : "c" (control),
-	    "d" (input_pa), "m" (sc->sc_hc));
+	extern uint64_t hv_hypercall_trampoline(uint64_t, paddr_t, paddr_t);
+	status = hv_hypercall_trampoline(control, input_pa, output_pa);
 #else  /* __i386__ */
 	{
 		uint32_t control_hi = control >> 32;