Merge "Remove an old demo."
am: c11104dd31
Change-Id: I2123ed25a29caeb5dea7c9a7747b6cd401e502ed
This commit is contained in:
Elliott Hughes
@@ -1,28 +0,0 @@
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# Copyright (C) 2013 The Android Open Source Project
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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ifneq ($(filter arm ,$(TARGET_ARCH)),)
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LOCAL_PATH:= $(call my-dir)
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include $(CLEAR_VARS)
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LOCAL_SRC_FILES:= main.c.arm
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LOCAL_CFLAGS := -std=gnu99 -O0
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LOCAL_MODULE := reverse_debug
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include $(BUILD_EXECUTABLE)
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endif # arm in TARGET_ARCH
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@@ -1,137 +0,0 @@
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This is a tutorial/unittest for gdb's reverse debugging feature. It is a new
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feature that allows users to take a snapshot of the machine state, continue
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until a later stage of the program, then return to the previously recorded
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state and execute again. An ideal usage case is to help track down the reason
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why a memory location is clobbered.
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In the sample below, the "clobber" function trashes a neighboring variable "p"
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on the stack next to the "values" variable, and the program will crash at
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line 42 when "p" is being dereferenced.
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18 #include <stdio.h>
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19 #include <stdlib.h>
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20
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21 #define ARRAY_LENGTH 10
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22
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23 int flag;
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24
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25 void clobber(int *array, int size) {
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26 /* Make sure it clobbers something. */
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27 array[-1] = 0x123;
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28 array[size] = 0x123;
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29 }
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30
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31 int main(void) {
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32 int values[ARRAY_LENGTH];
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33 int *p = (int *) malloc(sizeof(int));
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34 *p = 10;
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35
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36 while (!flag) {
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37 sleep(1);
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38 }
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39
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40 /* Set a breakpint here: "b main.c:41" */
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41 clobber(values, ARRAY_LENGTH);
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42 printf("*p = %d\n", *p);
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43 free(p);
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44
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45 return 0;
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46 }
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The test program can be built/installed on the device by doing:
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> mmm development/tutorials/ReverseDebug
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> adb sync
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> adb shell reverse_debug
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In another window the following command can be used to attach to the running
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program:
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> gdbclient reverse_debug :5039 reverse_debug
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[1] 12802
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Attached; pid = 1842
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Listening on port 5039
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GNU gdb (GDB) 7.6
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Copyright (C) 2013 Free Software Foundation, Inc.
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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This is free software: you are free to change and redistribute it.
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There is NO WARRANTY, to the extent permitted by law. Type "show copying"
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and "show warranty" for details.
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This GDB was configured as "--host=x86_64-linux-gnu --target=arm-linux-android".
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For bug reporting instructions, please see:
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<http://source.android.com/source/report-bugs.html>...
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Reading symbols from /usr/local/google/work/master/out/target/product/manta/symbols/system/bin/reverse_debug...done.
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Remote debugging from host 127.0.0.1
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nanosleep () at bionic/libc/arch-arm/syscalls/nanosleep.S:10
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10 mov r7, ip
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====
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Now set a breakpoint on line 41 and set flag to 1 so that the program can
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continue.
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(gdb) b main.c:41
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Breakpoint 1 at 0xb6f174a8: file development/tutorials/ReverseDebug/main.c, line 41.
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(gdb) p flag=1
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$1 = 1
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(gdb) c
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Continuing.
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====
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Now try the new "record" command to take a snapshot of the machine state.
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Breakpoint 1, main () at development/tutorials/ReverseDebug/main.c:41
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41 clobber(values, ARRAY_LENGTH);
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(gdb) record
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(gdb) c
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Continuing.
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====
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Now the program crashes as expected as "p" has been clobbered. The
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"reverse-continue" command will bring the program back to line 41 and let you
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replay each instruction from there.
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Program received signal SIGSEGV, Segmentation fault.
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0xb6f174bc in main () at development/tutorials/ReverseDebug/main.c:42
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42 printf("*p = %d\n", *p);
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(gdb) reverse-continue
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Continuing.
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No more reverse-execution history.
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main () at development/tutorials/ReverseDebug/main.c:41
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41 clobber(values, ARRAY_LENGTH);
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====
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Now let's add a watch point at "&p" to hopefully catch the clobber on the spot:
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(gdb) watch *(&p)
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Hardware watchpoint 2: *(&p)
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(gdb) c
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Continuing.
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Hardware watchpoint 2: *(&p)
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====
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And here it is:
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Old value = (int *) 0xb728c020
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New value = (int *) 0x123
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0xb6f17440 in clobber (array=0xbebcaab0, size=10)
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at development/tutorials/ReverseDebug/main.c:28
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28 array[size] = 0x123;
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===============================
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That said, reverse debugging on ARM is still in the infant stage. Currently
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(as of gdb 7.6) it only recognizes ARM instructions and will punt on all
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Thumb(2) instructions. To give it a try you will need to recompile your
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program in ARM mode. To do that you have to add the ".arm" suffix to the
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desired file in Android.mk:
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LOCAL_SRC_FILES:= main.c.arm
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@@ -1,47 +0,0 @@
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/*
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* Copyright (C) 2013 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#define ARRAY_LENGTH 10
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int flag;
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void clobber(int *array, int size) {
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/* Make sure it clobbers something. */
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array[-1] = 0x123;
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array[size] = 0x123;
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}
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int main(void) {
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int values[ARRAY_LENGTH];
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int *p = (int *) malloc(sizeof(int));
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*p = 10;
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while (!flag) {
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sleep(1);
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}
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/* Set a breakpint here: "b main.c:41" */
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clobber(values, ARRAY_LENGTH);
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printf("*p = %d\n", *p);
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free(p);
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return 0;
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}
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