// gcRemoveStackBarrier removes a single stack barrier. It is the
// inverse operation of gcInstallStackBarrier.
//
// This is nosplit to ensure gp's stack does not move.
//
//go:nowritebarrier
//go:nosplit
func gcRemoveStackBarrier(gp *g, stkbar stkbar) {
if debugStackBarrier {
print("remove stack barrier at ", hex(stkbar.savedLRPtr), " with ", hex(stkbar.savedLRVal), ", goid=", gp.goid, "\n")
}
lrPtr := (*sys.Uintreg)(unsafe.Pointer(stkbar.savedLRPtr))
if val := *lrPtr; val != sys.Uintreg(stackBarrierPC) {
printlock()
print("at *", hex(stkbar.savedLRPtr), " expected stack barrier PC ", hex(stackBarrierPC), ", found ", hex(val), ", goid=", gp.goid, "\n")
print("gp.stkbar=")
gcPrintStkbars(gp, -1)
print(", gp.stack=[", hex(gp.stack.lo), ",", hex(gp.stack.hi), ")\n")
throw("stack barrier lost")
}
*lrPtr = sys.Uintreg(stkbar.savedLRVal)
}
// gcInstallStackBarrier installs a stack barrier over the return PC of frame.
//go:nowritebarrier
func gcInstallStackBarrier(gp *g, frame *stkframe) bool {
if frame.lr == 0 {
if debugStackBarrier {
print("not installing stack barrier with no LR, goid=", gp.goid, "\n")
}
return false
}
if frame.fn.entry == cgocallback_gofuncPC {
// cgocallback_gofunc doesn't return to its LR;
// instead, its return path puts LR in g.sched.pc and
// switches back to the system stack on which
// cgocallback_gofunc was originally called. We can't
// have a stack barrier in g.sched.pc, so don't
// install one in this frame.
if debugStackBarrier {
print("not installing stack barrier over LR of cgocallback_gofunc, goid=", gp.goid, "\n")
}
return false
}
// Save the return PC and overwrite it with stackBarrier.
var lrUintptr uintptr
if usesLR {
lrUintptr = frame.sp
} else {
lrUintptr = frame.fp - sys.RegSize
}
lrPtr := (*sys.Uintreg)(unsafe.Pointer(lrUintptr))
if debugStackBarrier {
print("install stack barrier at ", hex(lrUintptr), " over ", hex(*lrPtr), ", goid=", gp.goid, "\n")
if uintptr(*lrPtr) != frame.lr {
print("frame.lr=", hex(frame.lr))
throw("frame.lr differs from stack LR")
}
}
gp.stkbar = gp.stkbar[:len(gp.stkbar)+1]
stkbar := &gp.stkbar[len(gp.stkbar)-1]
stkbar.savedLRPtr = lrUintptr
stkbar.savedLRVal = uintptr(*lrPtr)
*lrPtr = sys.Uintreg(stackBarrierPC)
return true
}
