In previous articles, I was not able to use Qt’s debug package provided by Ubuntu. Now, I will explain how to use them.
Our simple application:
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// main.cpp #include <QtCore/QString> int main() { QString s = "1234567"; int i = s.indexOf('3'); return i != 2; } |
Our *.pro file, you should enable the debug build:
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# DebugQt.pro TARGET = DebugQt TEMPLATE = app SOURCES += main.cpp QT -= gui CONFIG += console debug_and_release |
1. Build your debug version of application:
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# qmake-qt4 # make debug |
2. Install Qt’s debug package:
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# sudo apt-get install libqt4-debug |
3. Install the Qt source:
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# sudo apt-get source libqt4-debug |
Now you can start debugging your application. Since Qt’s debug symbols are installed in /usr/lib, It does not follow the GDB’s global debug directory described here. We should tell GDB to load these symbols manually:
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# gdb ./DebugQt GNU gdb 6.8-debian ... (gdb) b main Breakpoint 1 at 0x8048696: file main.cpp, line 3. (gdb) r Starting program: /home/binson/DebugQt/DebugQt [Thread debugging using libthread_db enabled] [New Thread 0xb71d36c0 (LWP 11138)] [Switching to Thread 0xb71d36c0 (LWP 11138)] Breakpoint 1, main () at main.cpp:3 3 QString s = "1234567"; (gdb) info sharedlibrary From To Syms Read Shared Object Library 0xb77a47f0 0xb77b96df Yes /lib/ld-linux.so.2 0xb7652510 0xb7740904 Yes /usr/lib/libQtCore.so.4 0xb7605210 0xb7610a04 Yes /lib/tls/i686/cmov/libpthread.so.0 0xb754fa60 0xb75ccb14 Yes /usr/lib/libstdc++.so.6 0xb74eb440 0xb7505414 Yes /lib/tls/i686/cmov/libm.so.6 0xb74de970 0xb74e5e04 Yes /lib/libgcc_s.so.1 0xb73a4230 0xb74a4ea4 Yes /lib/tls/i686/cmov/libc.so.6 0xb7368470 0xb7380684 Yes /usr/lib/libfontconfig.so.1 0xb7350910 0xb735e3e4 Yes /usr/lib/libz.so.1 0xb734a180 0xb734b804 Yes /usr/lib/libgthread-2.0.so.0 0xb7341990 0xb7345ee4 Yes /lib/tls/i686/cmov/librt.so.1 0xb72a0620 0xb72fe114 Yes /usr/lib/libglib-2.0.so.0 0xb728ba70 0xb728ca74 Yes /lib/tls/i686/cmov/libdl.so.2 0xb72249f0 0xb7276264 Yes /usr/lib/libfreetype.so.6 0xb71fe190 0xb7214384 Yes /usr/lib/libexpat.so.1 0xb71d5ef0 0xb71f1da4 Yes /usr/lib/libpcre.so.3 |
We set a breakpoint at the beginning of main function to load all shared libraries. Next, we will load symbols for libQtCore.so.4. The symbol will be loaded in the start address of it (0xb7652510):
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(gdb) add-symbol-file /usr/lib/libQtCore.so.4.3.4.debug 0xb7652510 add symbol table from file "/usr/lib/libQtCore.so.4.3.4.debug" at .text_addr = 0xb7652510 (y or n) y Reading symbols from /usr/lib/libQtCore.so.4.3.4.debug...done. |
Now, you are able to step into the Qt library, but no source is attached:
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(gdb) b 4 Breakpoint 2 at 0x80486a9: file main.cpp, line 4. (gdb) c Continuing. Breakpoint 2, main () at main.cpp:4 4 int i = s.indexOf('3'); (gdb) s QChar (this=0xbfb1ec0e, ch=51 '3') at tools/qchar.cpp:432 432 tools/qchar.cpp: No such file or directory. in tools/qchar.cpp |
Source files are attached by:
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(gdb) dir ~/qt4-x11-4.3.4/src/corelib Source directories searched: /home/binson/qt4-x11-4.3.4/src/corelib:$cdir:$cwd (gdb) l 427 428 /*! 429 Constructs a QChar corresponding to ASCII/Latin-1 character \a 430 ch. 431 */ 432 QChar::QChar(char ch) 433 { 434 #ifndef QT_NO_CODEC_FOR_C_STRINGS 435 if (QTextCodec::codecForCStrings()) 436 // ##### (gdb) bt #0 QChar (this=0xbfb1ec0e, ch=51 '3') at tools/qchar.cpp:432 #1 0x080486bc in main () at main.cpp:4 |
See the source and backtrace? 🙂