2019.10.25

oslab/README.txt

@@ -0,0 +1,34 @@
+# 实验篇
+
+1. shell 脚本问题
+
+*.bxrc 文件中的变量不要用`{}`包起来，例如要用`$OSLAB_PATH`，不要用`${OSLAB_PATH}`。否则会找不到变量。
+
+2. 如何使bochs、gdb调试忽略page fault信号？
+
+Created a patch "gdbstub.cc.patch" against bochs (version CVS 20080110)
+   Bochs always tries to find out the reason of an exception, so that it can generate the right signal for gdb.
+   If it fails to find a reason, bochs assigns a value GDBSTUB_STOP_NO_REASON (see bochs.h), which causes
+   debug_loop() (see gdbstub.cc) to generate a signal of number 0.
+   Signal 0 is problematic to gdb, as gdb doesn't allow us to ignore it.
+   Somehow when we simulate linux, we get tons of signal 0's that seem to be caused by page faults.
+   This patch makes bochs send SIGSEGV instead of signal 0, so that we can ignore it in gdb.
+
+gdbstub.cc
+debug_loop()
+
+*** gdbstub.cc.orig Thu Oct 18 18:44:38 2007
+--- gdbstub.cc Sat Jan 12 17:25:22 2008
+*************** static void debug_loop(void)
+*** 489,494 ****
+--- 489,498 ----
+          {
+            write_signal(&buf[1], SIGTRAP);
+          }
++  else if (last_stop_reason == GDBSTUB_STOP_NO_REASON)
++  {
++    write_signal(&buf[1], SIGSEGV);
++  }
+          else
+          {
+            write_signal(&buf[1], 0);