get_tls(CX)
MOVQ g(CX), BP
MOVQ g_m(BP), BP
+
+ // Set m->sched.sp = SP, so that if a panic happens
+ // during the function we are about to execute, it will
+ // have a valid SP to run on the g0 stack.
+ // The next few lines (after the havem label)
+ // will save this SP onto the stack and then write
+ // the same SP back to m->sched.sp. That seems redundant,
+ // but if an unrecovered panic happens, unwindm will
+ // restore the g->sched.sp from the stack location
+ // and then onM will try to use it. If we don't set it here,
+ // that restored SP will be uninitialized (typically 0) and
+ // will not be usable.
+ MOVQ m_g0(BP), SI
+ MOVQ SP, (g_sched+gobuf_sp)(SI)
havem:
// Now there's a valid m, and we're running on its m->g0.