fix(debug): handle mapping edges, stray traps and dying debuggees

Assisted-by: GLM 5.3

debug/watchpoint_freebsd_arm64.go

@@ -7,6 +7,7 @@ package debug
 
 import (
 	"fmt"
+	"math/bits"
 	"unsafe"
 
 	"golang.org/x/sys/unix"
@@ -83,7 +84,10 @@ func (s *Session) setDbRegs(dr *dbreg) error {
 // EXCP_SOFTSTP_EL0/EXCP_WATCHPT_EL0 with TRAP_TRACE (sys/arm64/arm64/
 // trap.c); the watchpoint address rides the FAR register, so a stop whose
 // reported address falls inside an armed watchpoint's byte range is a
-// watchpoint and everything else is a single step.
+// watchpoint and everything else is a single step.  The byte range comes
+// from DBGWCR's byte-address-select bits (ARM DDI 0487, DBGWCR<n>_EL1):
+// bit i watches the address plus i, so the range spans the lowest set bit
+// to the highest set bit inclusive.
 func archStopTrace(s *Session, siAddr uint64) (StopReason, uint64) {
 	dr, err := s.getDbRegs()
 	if err != nil {
@@ -94,7 +98,14 @@ func archStopTrace(s *Session, siAddr uint64) (StopReason, uint64) {
 		if ctrl&1 == 0 || dr.DbWatchregs[slot].Addr == 0 {
 			continue
 		}
-		if bas := (ctrl >> 5) & 0xFF; bas != 0 && siAddr >= dr.DbWatchregs[slot].Addr && siAddr < dr.DbWatchregs[slot].Addr+8 {
+		bas := uint8((ctrl >> 5) & 0xFF)
+		if bas == 0 {
+			continue
+		}
+		lo := bits.TrailingZeros8(bas)
+		hi := 7 - bits.LeadingZeros8(bas)
+		addr := dr.DbWatchregs[slot].Addr
+		if siAddr >= addr+uint64(lo) && siAddr < addr+uint64(hi)+1 {
 			return StopWatchpoint, siAddr
 		}
 	}