GDB Command Line Arguments

Starting GDB:

• gdb name-of-executable
• gdb -e name-of-executable -c name-of-core-file
• gdb name-of-executable -pid process-id
  (Use ps -auxw to list process id's.)

Command line options: (version 6. Older versions use a single "-")

OptionDescription--help
-hList command line arguments--exec=file-name
-e file-nameIdentify executable associated with core file.--core=name-of-core-file
-c name-of-core-fileSpecify core file.--command=command-file
-x command-fileFile listing GDB commands to perform. Good for automating set-up.--directory=directory
-d directoryAdd directory to the path to search for source files.--cd=directoryRun GDB using specified directory as the current working directory.--nx
-nDo not execute commands from ~/.gdbinit initialization file. Default is to look at this file and execute the list of commands.--batch -x command-fileRun in batch (not interactive) mode. Execute commands from file. Requires -x option.--symbols=file-name
-s file-nameRead symbol table from file file.--writeEnable writing into executable and core files.--quiet
-qDo not print the introductory and copyright messages.--tty=deviceSpecify device for running program's standard input and output.--pid=process-id
-p process-id
-c process-idSpecify process ID number to attach to.

 

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GDB Commands:

Commands used within GDB:

 

CommandDescriptionhelpList gdb command topics.help topic-classesList gdb command within class.help commandCommand description.apropos search-wordSearch for commands and command topics containing search-word.info args
i argsList program command line argumentsinfo breakpointsList breakpointsinfo breakList breakpoint numbers.info break breakpoint-numberList info about specific breakpoint.info watchpointsList breakpointsinfo registersList registers in useinfo threadsList threads in useinfo setList set-able optionBreak and Watch
break funtion-name
break line-numberSuspend program at specified function of line number.
break ClassName::functionNamebreak +offset
break -offsetSet a breakpoint specified number of lines forward or back from the position at which execution stopped.break filename:functionDon't specify path, just the file name and function name.break filename:line-numberDon't specify path, just the file name and line number.
break Directory/Path/filename.cpp:62break *addressSuspend processing at an instruction address. Used when you do not have source.break line-number if conditionWhere condition is an expression. i.e. x > 5
Suspend when boolean expression is true.break line thread thread-numberBreak in thread at specified line number. Use info threads to display thread numbers.tbreakTemporary break. Break once only. Break is then removed. See "break" above for options.watch conditionSuspend processing when condition is met. i.e. x > 5clear
clear function
clear line-numberDelete breakpoints as identified by command option.delete
dDelete all breakpoints, watchpoints, or catchpoints.delete breakpoint-number
delete rangeDelete the breakpoints, watchpoints, or catchpoints of the breakpoint ranges specified as arguments.disable breakpoint-number-or-range
enable breakpoint-number-or-rangeDoes not delete breakpoints. Just enables/disables them.
Example:
Show breakpoints: info break
Disable: disable 2-9enable breakpoint-number onceEnables oncecontinue
cContinue executing until next break point/watchpoint.continue numberContinue but ignore current breakpoint number times. Usefull for breakpoints within a loop.finishContinue to end of function.Line Execution
step
s
step number-of-steps-to-performStep to next line of code. Will step into a function.next
n
next numberExecute next line of code. Will not enter functions. until
until line-numberContinue processing until you reacha aspecified line number. Also: function name, address, filename:function or filename:line-number.stepi
si
nexti
nistep/next assembly/processor instruction.info signals
info handle
handle SIGNAL-NAME optionPerform the following option when signal recieved: nostop, stop, print, noprint, pass/noignore or nopass/ignorewhereShows current line number and which function you are in.Stack
backtrace
bt
bt inner-function-nesting-depth
bt -outer-function-nesting-depthShow trace of where you are currently. Which functions you are in. Prints stack backtrace.backtrace fullPrint values of local variables.frame number
f numberSelect frame number.up number
down numberMove up/down the specified number of frames in the stack.info frameList address, language, address of arguments/local variables and which registers were saved in frame.info args
info locals
info catchInfo arguments of selected frame, local variables and exception handlers.Source Code
list
l
list line-number
list function
list -
list start#,end#
list filename:functionList source code.set listsize count
show listsizeNumber of lines listed when list command given.directory directory-name
dir directory-name
show directoriesAdd specified directory to front of source code path.directoryClear sourcepath when nothing specified.Examine Variables
print variable-name
p variable-name
p file-name::variable-name
p 'file-name'::variable-namePrint value stored in variable.p *array-variable@lengthPrint first # values of array specified by length. Good for pointers to dynamicaly allocated memory.p/x variablePrint as integer variable in hex.p/d variablePrint variable as a signed integer.p/u variablePrint variable as a un-signed integer.p/o variablePrint variable as a octal.p/t variable
x/b address
x/b &variablePrint as integer value in binary. (1 byte/8bits)p/c variablePrint integer as character.p/f variablePrint variable as floating point number.p/a variablePrint as a hex address.x/w address
x/4b &variablePrint binary representation of 4 bytes (1 32 bit word) of memory pointed to by address.GDB Modes
set gdb-option valueSet a GDB optionset logging on
set logging off
show logging
set logging file log-fileTurn on/off logging. Default name of file is gdb.txtset print array on
set print array off
show print arrayDefault is off. Convient readable format for arrays turned on/off.set print array-indexes on
set print array-indexes off
show print array-indexesDefault off. Print index of array elements.set print pretty on
set print pretty off
show print prettyFormat printing of C structures.set print union on
set print union off
show print unionDefault is on. Print C unions.set print demangle on
set print demangle off
show print demangleDefault on. Controls printing of C++ names.Start and Stop
run
r
run command-line-arguments
run < infile > outfileStart program execution from the beginning of the program. The command break main will get you started. Also allows basic I/O redirection.continue
cContinue execution to next break point.killStop program execution.quit
qExit GDB debugger.

 

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GDB Operation:

 

• Compile with the "-g" option (for most GNU and Intel compilers) which generates added information in the object code so the debugger can match a line of source code with the step of execution.
• Do not use compiler optimization directive such as "-O" or "-O2" which rearrange computing operations to gain speed as this reordering will not match the order of execution in the source code and it may be impossible to follow.
• control+c: Stop execution. It can stop program anywhere, in your source or a C library or anywhere.
• To execute a shell command: ! command
  or shell command
• GDB command completion: Use TAB key
  info bre + TAB will complete the command resulting in info breakpoints
  Press TAB twice to see all available options if more than one option is available or type "M-?" + RETURN.
• GDB command abreviation:
  info bre + RETURN will work as bre is a valid abreviation for breakpoints

 

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De-Referencing STL Containers:

Displaying STL container classes using the GDB "p variable-name" results in an cryptic display of template definitions and pointers. Use the following ~/.gdbinit file (V1.03 09/15/08). Now works with GDB 4.3+.
(Archived versions: [V1.01 GDB 6.4+ only])
Thanks to Dr. Eng. Dan C. Marinescu for permission to post this script.

Use the following commands provided by the script:

Data typeGDB commandstd::vector<T>pvector stl_variablestd::list<T>plist stl_variable Tstd::map<T,T>pmap stl_variablestd::multimap<T,T>pmap stl_variablestd::set<T>pset stl_variable Tstd::multiset<T>pset stl_variablestd::deque<T>pdequeue stl_variablestd::stack<T>pstack stl_variablestd::queue<T>pqueue stl_variablestd::priority_queue<T>ppqueue stl_variablestd::bitset<n>td> pbitset stl_variablestd::stringpstring stl_variablestd::widestringpwstring stl_variableWhere T refers to native C++ data types. While classes and other STL data types will work with the STL container classes, this de-reference tool may not handle non-native types.

 

Also see the YoLinux.com STL string class tutorial and debugging with GDB.

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De-Referencing a vector:

Example: STL_vector_int.cpp

view source

print?

01#include <iostream>

02#include <vector>

03#include <string>

04  

05using namespace std;

06  

07main()

08{

09   vector<int> II;

10  

11   II.push_back(10);

12   II.push_back(20);

13   II.push_back(30);

14  

15   cout << II.size() << endl;

16  

17}

Compile: g++ -g STL_vector_int.cpp

Debug in GDB: gdb a.out

(gdb) l1       #include <iostream>2       #include <vector>3       #include <string>45       using namespace std;67       main()8       {9          vector<int> II;10(gdb) l11         II.push_back(10);12         II.push_back(20);13         II.push_back(30);1415         cout << II.size() << endl;1617      }(gdb) break 15Breakpoint 1 at 0x8048848: file STL_vector_int.cpp, line 15.(gdb) rStarting program: /home/userx/a.outBreakpoint 1, main () at STL_vector_int.cpp:1515         cout << II.size() << endl;(gdb) p II$1 = {  <std::_Vector_base<int,std::allocator<int> >> = {    _M_impl = {      <std::allocator<int>> = {        <__gnu_cxx::new_allocator<int>> = {<No data fields>}, <No data fields>},      members of std::_Vector_base<int,std::allocator<int> >::_Vector_impl:      _M_start = 0x804b028,      _M_finish = 0x804b034,      _M_end_of_storage = 0x804b038    }  }, <No data fields>}(gdb) pvector IIelem[0]: $2 = 10elem[1]: $3 = 20elem[2]: $4 = 30Vector size = 3Vector capacity = 4Element type = int *(gdb) cContinuing.3Program exited normally.(gdb) quit

Notice the native GDB print "p" results in an cryptic display while the "pvector" routine from the GDB script provided a human decipherable display of your data.

 

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De-Referencing a 2-D vector of vectors:

Example: STL_vector_int_2.cpp

view source

print?

01#include <iostream>

02#include <vector>

03  

04using namespace std;

05  

06main()

07{

08   vector< vector<int> > vI2Matrix(3, vector<int>(2,0));

09  

10   vI2Matrix[0][0] = 0;

11   vI2Matrix[0][1] = 1;

12   vI2Matrix[1][0] = 10;

13   vI2Matrix[1][1] = 11;

14   vI2Matrix[2][0] = 20;

15   vI2Matrix[2][1] = 21;

16  

17   cout << "Loop by index:" << endl;

18  

19   int ii, jj;

20   for(ii=0; ii < 3; ii++)

21   {

22      for(jj=0; jj < 2; jj++)

23      {

24         cout << vI2Matrix[ii][jj] << endl;

25      }

26   }

27}

Compile: g++ -g STL_vector_int_2.cpp

Debug in GDB: gdb a.out

(gdb) l1       #include <iostream>2       #include <vector>34       using namespace std;56       main()7       {8          vector< vector<int> > vI2Matrix(3, vector<int>(2,0));910         vI2Matrix[0][0] = 0;(gdb) l11         vI2Matrix[0][1] = 1;12         vI2Matrix[1][0] = 10;13         vI2Matrix[1][1] = 11;14         vI2Matrix[2][0] = 20;15         vI2Matrix[2][1] = 21;1617         cout << "Loop by index:" << endl;1819         int ii, jj;20         for(ii=0; ii < 3; ii++)(gdb) break 17Breakpoint 1 at 0x8048a19: file STL_vector_2.cpp, line 17.(gdb) rStarting program: /home/userx/a.outBreakpoint 1, main () at STL_vector_2.cpp:1717         cout << "Loop by index:" << endl;(gdb) pvector vI2Matrixelem[0]: $1 = {  <std::_Vector_base<int,std::allocator<int> >> = {    _M_impl = {      <std::allocator<int>> = {        <__gnu_cxx::new_allocator<int>> = {<No data fields>}, <No data fields>},      members of std::_Vector_base<int,std::allocator<int> >::_Vector_impl:      _M_start = 0x804b040,      _M_finish = 0x804b048,      _M_end_of_storage = 0x804b048    }  }, <No data fields>}elem[1]: $2 = {  <std::_Vector_base<int,std::allocator<int> >> = {    _M_impl = {      <std::allocator<int>> = {        <__gnu_cxx::new_allocator<int>> = {<No data fields>}, <No data fields>},      members of std::_Vector_base<int,std::allocator<int> >::_Vector_impl:      _M_start = 0x804b050,      _M_finish = 0x804b058,      _M_end_of_storage = 0x804b058    }  }, <No data fields>}elem[2]: $3 = {  <std::_Vector_base<int,std::allocator<int> >> = {    _M_impl = {      <std::allocator<int>> = {        <__gnu_cxx::new_allocator<int>> = {<No data fields>}, <No data fields>},      members of std::_Vector_base<int,std::allocator<int> >::_Vector_impl:      _M_start = 0x804b060,      _M_finish = 0x804b068,      _M_end_of_storage = 0x804b068---Type <return> to continue, or q <return> to quit---    }  }, <No data fields>}Vector size = 3Vector capacity = 3Element type = class std::vector<int,std::allocator<int> > *(gdb) pvector $1elem[0]: $4 = 0elem[1]: $5 = 1Vector size = 2Vector capacity = 2Element type = int *(gdb) pvector $2elem[0]: $6 = 10elem[1]: $7 = 11Vector size = 2Vector capacity = 2Element type = int *(gdb) pvector $3elem[0]: $8 = 20elem[1]: $9 = 21Vector size = 2Vector capacity = 2Element type = int *(gdb) p vI2Matrix$10 = {  <std::_Vector_base<std::vector<int, std::allocator<int> >,std::allocator<std::vector<int, std::allocator<int> > > >> = {    _M_impl = {      <std::allocator<std::vector<int, std::allocator<int> > >> = {        <__gnu_cxx::new_allocator<std::vector<int, std::allocator<int> > >> = {<No data fields>}, <No data fields>},      members of std::_Vector_base<std::vector<int, std::allocator<int> >,std::allocator<std::vector<int, std::allocator<int> > > >::_Vector_impl:      _M_start = 0x804b018,      _M_finish = 0x804b03c,      _M_end_of_storage = 0x804b03c    }  }, <No data fields>}(gdb) quit

Note "pvector" does not de-reference the entire vector of vectors all at once but returns vectors $1, $2 and $3. The "pvector" command then helps us traverse the information by examining the contents of each element in the individual "terminal" vectors. Note that the native gdb "p vI2Matrix" (last command) was much less informative.