Return zeros when GDB reads just past end of stack.

[simavr] / simavr / sim / sim_gdb.c

diff --git a/simavr/sim/sim_gdb.c b/simavr/sim/sim_gdb.c
index f2d46ff..9bec4b5 100644 (file)
--- a/simavr/sim/sim_gdb.c
+++ b/simavr/sim/sim_gdb.c
@@ -208,6 +208,12 @@ static void gdb_handle_command(avr_gdb_t * g, char * cmd)
                                        gdb_send_reply(g, "E01");
                                        break;
                                }
+                       } else if (addr >= 0x800000 && (addr - 0x800000) == avr->ramend+1 && len == 2) {
+                               // Allow GDB to read a value just after end of stack.
+                               // This is necessary to make instruction stepping work when stack is empty
+                               printf("GDB read just past end of stack %08x, %08x; returning zero\n", addr, len);
+                               gdb_send_reply(g, "0000");
+                               break;
                        } else {
                                printf("read memory error %08x, %08x (ramend %04x)\n", addr, len, avr->ramend+1);
                                gdb_send_reply(g, "E01");