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PB173 - Tématický vývoj aplikací v
C/C++ (podzim 2013)
Skupina: Aplikovaná kryptografie a bezpečné
programování
https://minotaur.fi.muni.cz:8443/pb173_crypto
Petr Švenda, svenda@fi.muni.cz
Konzultace: G201, Úterý 13-13:50
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Debugging with debugger
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Release vs. Debug
Optimizations applied (compiler-specific settings)
● gcc –Ox (http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html)
● -O0 no optimization (Debug)
● -Og debug-friendly optimization
● -O3 heavy optimization
● msvc /Ox /Oi (http://msdn.microsoft.com/en-us/library/k1ack8f1.aspx)
● MSVS2010: Project properties→C/C++→optimizations
Availability of debug information (symbols)
● gcc –g
● symbols inside binary
● msvc /Z7, /Zi
● symbols in detached file ($projectname.pdb)
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Debugger commands (MSVC shortcuts)
http://www.fi.muni.cz/~xsvenda/VS_debugging.html
http://cecko.eu/public/qtcreator#debugging
Insert breakpoint F9
Run in debug mode F5
Step over, step into F10, F11
Watch variable (Autos, Locals, Watch)
● R-Click → Add watch
● R-Click on variable (Decimal ↔ Hexadecimal display)
Change variable (Watch tab)
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Debugger commands (2)
Conditional breakpoint
● Insert breakpoint & R-Click (MSVS2010), Edit breakpoint (QTC)
● Condition…, Hit count…, When hit…
● Filter… (multithreading)
Data breakpoint (MSVS2010)
● First run in debug mode
● Debug → New breakpoint → New data breakpoint
● &(temp[5]), size 4
● (must be address of memory by &, not only temp[5])
Disassembly info
● MSVS2010: Run debug, R-Click → Go to disassembly
● QTC: Debug → Operate by instruction
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Edit and Continue
Possibility to continue in debugging session even after
code change (fix of partial “bug”)
● Code is changed, recompiled and debugging continues
Supported by only some IDE/Debuggers (MSVS)
Edit and continue
● Must be enabled before symbols are generated
● Properties → C/C++ → General → Debug information format
Possibility to move instruction pointer to ordinary place
● Move arrow to any line in code, IP is updated
● Usually moved only few instructions above current IP (same
function)
● Be careful: only IP is updated, not the stack etc.
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Debugger commands (3)
Debugging of Release binary
● possible, similar to Debug mode
● but asm code with optimizations
● with or without symbols
● WinDbg
Debugging of running process
● MSVS2010: Debug → Attach to process
Reverse engineering
● OllyDbg, http://www.ollydbg.de/
● IDAPro http://www.hex-rays.com/products/ida/index.shtml
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Additional reading
http://eli.thegreenplace.net/programs-and-
code/how-debuggers-work/
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Practical assignment
Implement API functions relevant for client authentication
to server and obtain list of other online clients