After setting a breakpoint in Qt, gdb says: "Error accessing memory address"

Question

I wrote a very simple Qt program here:

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);

    QTableView table(&frame);
    table.resize(100, 100);
    table.show();

    return app.exec();
}

And when I try to set a breakpoint where the table gets clicked, I get this error from gdb:

(gdb) symbol-file /usr/lib/libQtGui.so.4.4.3.debug 
Load new symbol table from "/usr/lib/libQtGui.so.4.4.3.debug"? (y or n) y
Reading symbols from /usr/lib/libQtGui.so.4.4.3.debug...done.
(gdb) br 'QAbstractItemView::clicked(QModelIndex const&)'
Breakpoint 1 at 0x5fc660: file .moc/release-shared/moc_qabstractitemview.cpp, line 313.
(gdb) run
Starting program: ./qt-test
Warning:
Cannot insert breakpoint 1.
Error accessing memory address 0x5fc660: Input/output error.

Does anyone know why the breakpoint can't be inserted?

Answer 1

Don't use the gdb command symbol-file to load external symbols. The breakpoint addresses will be wrong since they're not relocated.

Instead, put a breakpoint in main, run the program, and then set your breakpoint:

gdb ./program
GNU gdb 6.8-debian blah blah blah
(gdb) br main
Breakpoint 1 at 0x80489c1
(gdb) run
Starting program: ./program
Breakpoint 1, 0x080489c1 in main ()
(gdb) br 'QAbstractItemView::clicked(QModelIndex const&)'
Breakpoint 2 at 0xb7d24664
(gdb) continue
Continuing.

Then make your breakpoint happen.

Make sure to specify the parameter list in the function you want to set a breakpoint in, without the names of those parameters, just their types.

Answer 2

The actual error:

Error accessing memory address 0x5fc660: Input/output error.

Can be caused by 32/64 bit mixups. Check, for example, that you didn't attach to a 32-bit binary with a 64-bit process' ID, or vice versa.