gdb: add more cmd and history stuff

.gdbinit

@@ -9,3 +9,19 @@ define exit
 kill
 quit
 end
+
+define xxd
+  dump binary memory /tmp/dump.bin $arg0 ((char *)$arg0)+$arg1
+  shell xxd /tmp/dump.bin
+end
+document xxd
+  Runs xxd on a memory ADDR and LENGTH
+
+  xxd ADDR LENTH
+end
+
+macro define offsetof(t, f) &((t *) 0)->f
+
+set history save on
+set history size 10000
+set history filename ~/.gdb_history