Starting GDB:
Command line options: (version 6. Older versions use a single "-")
Option | Description |
---|---|
--help -h | List command line arguments |
--exec=file-name -e file-name | Identify executable associated with core file. |
--core=name-of-core-file -c name-of-core-file | Specify core file. |
--command=command-file -x command-file | File listing GDB commands to perform. Good for automating set-up. |
--directory=directory -d directory | Add directory to the path to search for source files. |
--cd=directory | Run GDB using specified directory as the current working directory. |
--nx -n | Do not execute commands from ~/.gdbinit initialization file. Default is to look at this file and execute the list of commands. |
--batch -x command-file | Run in batch (not interactive) mode. Execute commands from file. Requires -x option. |
--symbols=file-name -s file-name | Read symbol table from file file. |
--write | Enable writing into executable and core files. |
--quiet -q | Do not print the introductory and copyright messages. |
--tty=device | Specify device for running program's standard input and output. |
--pid=process-id -p process-id -c process-id | Specify process ID number to attach to. |
GDB Commands: |
Commands used within GDB:
Command | Description |
---|---|
help | List gdb command topics. |
help topic-classes | List gdb command within class. |
help command | Command description. |
apropos search-word | Search for commands and command topics containing search-word. |
info args i args | List program command line arguments |
info breakpoints | List breakpoints |
info break | List breakpoint numbers. |
info break breakpoint-number | List info about specific breakpoint. |
info watchpoints | List breakpoints |
info registers | List registers in use |
info threads | List threads in use |
info set | List set-able option |
Break and Watch | |
break funtion-name break line-number break ClassName::functionName | Suspend program at specified function of line number. |
break +offset break -offset | Set a breakpoint specified number of lines forward or back from the position at which execution stopped. |
break filename:function | Don't specify path, just the file name and function name. |
break filename:line-number | Don't specify path, just the file name and line number. break Directory/Path/filename.cpp:62 |
break *address | Suspend processing at an instruction address. Used when you do not have source. |
break line-number if condition | Where condition is an expression. i.e. x > 5 Suspend when boolean expression is true. |
break line thread thread-number | Break in thread at specified line number. Use info threads to display thread numbers. |
tbreak | Temporary break. Break once only. Break is then removed. See "break" above for options. |
watch condition | Suspend processing when condition is met. i.e. x > 5 |
clear clear function clear line-number | Delete breakpoints as identified by command option. |
delete d | Delete all breakpoints, watchpoints, or catchpoints. |
delete breakpoint-number delete range | Delete the breakpoints, watchpoints, or catchpoints of the breakpoint ranges specified as arguments. |
disable breakpoint-number-or-range enable breakpoint-number-or-range | Does not delete breakpoints. Just enables/disables them. Example: Show breakpoints: info break Disable: disable 2-9 |
enable breakpoint-number once | Enables once |
continue c | Continue executing until next break point/watchpoint. |
continue number | Continue but ignore current breakpoint number times. Usefull for breakpoints within a loop. |
finish | Continue to end of function. |
Line Execution | |
step s step number-of-steps-to-perform | Step to next line of code. Will step into a function. |
next n next number | Execute next line of code. Will not enter functions. |
until until line-number | Continue processing until you reachaaspecified line number. Also: function name, address, filename:function or filename:line-number. |
stepi si nexti ni | step/next assembly/processor instruction. |
info signals info handle handle SIGNAL-NAME option | Perform the following option when signal recieved: nostop, stop, print, noprint, pass/noignore or nopass/ignore |
where | Shows current line number and which function you are in. |
Stack | |
backtrace bt bt inner-function-nesting-depth bt -outer-function-nesting-depth | Show trace of where you are currently. Which functions you are in. Prints stack backtrace. |
backtrace full | Print values of local variables. |
frame number f number | Select frame number. |
up number down number | Move up/down the specified number of frames in the stack. |
info frame | List address, language, address of arguments/local variables and which registers were saved in frame. |
info args info locals info catch | Info arguments of selected frame, local variables and exception handlers. |
Source Code | |
list l list line-number list function list - list start#,end# list filename:function | List source code. |
set listsize count show listsize | Number of lines listed when list command given. |
directory directory-name dir directory-name show directories | Add specified directory to front of source code path. |
directory | Clear sourcepath when nothing specified. |
Examine Variables | |
print variable-name p variable-name p file-name::variable-name p 'file-name'::variable-name | Print value stored in variable. |
p *array-variable@length | Print first # values of array specified by length. Good for pointers to dynamicaly allocated memory. |
p/x variable | Print as integer variable in hex. |
p/d variable | Print variable as a signed integer. |
p/u variable | Print variable as a un-signed integer. |
p/o variable | Print variable as a octal. |
p/t variable x/b address x/b &variable | Print as integer value in binary. (1 byte/8bits) |
p/c variable | Print integer as character. |
p/f variable | Print variable as floating point number. |
p/a variable | Print as a hex address. |
x/w address x/4b &variable | Print binary representation of 4 bytes (1 32 bit word) of memory pointed to by address. |
GDB Modes | |
set gdb-option value | Set a GDB option |
set logging on set logging off show logging set logging file log-file | Turn on/off logging. Default name of file is gdb.txt |
set print array on set print array off show print array | Default is off. Convient readable format for arrays turned on/off. |
set print array-indexes on set print array-indexes off show print array-indexes | Default off. Print index of array elements. |
set print pretty on set print pretty off show print pretty | Format printing of C structures. |
set print union on set print union off show print union | Default is on. Print C unions. |
set print demangle on set print demangle off show print demangle | Default on. Controls printing of C++ names. |
Start and Stop | |
run r run command-line-arguments run < infile > outfile | Start program execution from the beginning of the program. The command break main will get you started. Also allows basic I/O redirection. |
continue c | Continue execution to next break point. |
kill | Stop program execution. |
quit q | Exit GDB debugger. |
GDB Operation: |
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 type | GDB command |
---|---|
std::vector<T> | pvector stl_variable |
std::list<T> | plist stl_variable T |
std::map<T,T> | pmap stl_variable |
std::multimap<T,T> | pmap stl_variable |
std::set<T> | pset stl_variable T |
std::multiset<T> | pset stl_variable |
std::deque<T> | pdequeue stl_variable |
std::stack<T> | pstack stl_variable |
std::queue<T> | pqueue stl_variable |
std::priority_queue<T> | ppqueue stl_variable |
std::bitset<n>td> | pbitset stl_variable |
std::string | pstring stl_variable |
std::widestring | pwstring stl_variable |
Also see the YoLinux.com STL string class tutorial and debugging with GDB.
De-Referencing a vector: |
Example: 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 |
De-Referencing a 2-D vector of vectors: |
Example: 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 |
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