2019.10.25

oslab/README.txt

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+# 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);

oslab/bochs/.gdbrc

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+break main
+target remote localhost:1234
+handle SIGSEGV nostop noprint ignore
+continue

oslab/bochs/bochsrc-gdb.bxrc

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+romimage: file=$OSLAB_PATH/bochs/BIOS-bochs-latest
+megs: 32
+vgaromimage: file=$OSLAB_PATH/bochs/VGABIOS-lgpl-latest
+floppya: 1_44="$OSLAB_PATH/Image", status=inserted
+ata0-master: type=disk, path="$OSLAB_PATH/hdc.img", mode=flat, cylinders=204, heads=16, spt=38
+boot: floppy
+log: $OSLAB_PATH/bochsout.txt
+#parport1: enable=0
+cpu: count=1, ips=4000000
+gdbstub: enabled=1, port=1234, text_base=0, data_base=0, bss_base=0

oslab/bochs/bochsrc.bxrc

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+romimage: file=$OSLAB_PATH/bochs/BIOS-bochs-latest
+megs: 32
+vgaromimage: file=$OSLAB_PATH/bochs/VGABIOS-lgpl-latest
+floppya: 1_44="$OSLAB_PATH/Image", status=inserted
+ata0-master: type=disk, path="$OSLAB_PATH/hdc.img", mode=flat, cylinders=204, heads=16, spt=38
+boot: floppy
+log: $OSLAB_PATH/bochsout.txt
+cpu: count=1, ips=4000000

oslab/run.sh

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+#!/bin/sh
+export OSLAB_PATH=$(dirname `which $0`)
+
+if [ ! -e "hdc.img" ]; then
+tar -xvJf hdc.tar.xz
+fi
+
+if [ "$1" ] && [ "$1" = "-m" ]
+then
+(cd ../linux-0.12; make clean; make; cp Image ../oslab/Image)
+elif [ "$1" ] && [ "$1" = "-g" ]
+then
+$OSLAB_PATH/bochs/bochs-gdb -q -f $OSLAB_PATH/bochs/bochsrc-gdb.bxrc & \
+gdb -x $OSLAB_PATH/bochs/.gdbrc ../linux-0.12/tools/system
+else
+bochs -q -f $OSLAB_PATH/bochs/bochsrc.bxrc
+fi