GDB debug Manual [Go]

Linux contains a GNU debug program called GDB. GDB is a powerful debugger for debugging C and C + + programs. It allows you to observe the program's internal structure and memory usage while the program is running. Here are some of the features that GDB provides: It enables you to monitor the value of variables in your program, which allows you to set breakpoints so that the program stops executing on the specified line of code, and it enables you to execute your code in line. Type gdb on the command line and press ENTER to run GDB. (Windows needs to install MinGW or Cygwin and need to configure environment variables to use)

GDB command-line arguments

Start GDB:

L GDB Executable

L GDB-E executable-c Core-file

L GDB executable-pid Process-id

(Use command ' PS-AUXW ' to view PID of the process)

Options	Meaning
Help -H	Lists command-line arguments.
–exec=File -E file	Specifies the executable file.
–core=Core-file -C Core-file	Specifies the core file.
–command=File -X file	Reads the GDB command from the specified file.
–directory=Directory -D Directory	Adds the specified directory to the source file search path.
–cd=Directory	Runs GDB with the specified directory as the current path.
–nx -N	Do not execute the commands in the. gdbinit file. By default, the commands in this file are executed after all command-line arguments have been processed.
–batch	Run GDB in non-interactive mode. Commands are read from the file, so the-X option is required.
–symbols=File -S file	Reads the symbol table from the specified file.
-write	Allows write operations to executables and core files.
–quiet -Q	Do not print the introduction and copyright information.
–tty=Device	Specifies that device is the standard input output for running programs.
–pid=Process-id -P Process-id	Specifies the process ID to be attached.

GDB command

The commands used in GDB:

Command	Describe
Help	Lists GDB help information.
Help Topic	Lists the GDB commands in the related topic.
Help command	Lists command description information.
Apropos Search-word	Search for related topics.
Info args I-args	Lists the command-line arguments that run the program.
Info Breakpoints	Lists breakpoints.
Info break	Lists the breakpoint number.
Info Break Breakpoint-number	Lists information for the specified breakpoint.
Info watchpoints	Lists the observer points.
Info Registers	Lists the registers used.
Info threads	Lists the current thread.
Info set	Lists the options you can set.
Break and Watch
Break funtion Break Line-number	Sets a breakpoint at the specified function, or at the line number.
Break +Offset Break-Offset	Sets a breakpoint at the front or several lines in the current place of stay.
Break File:func	Sets a breakpoint at the func in the specified file file.
Break File:nth	Sets a breakpoint in the nth line in the specified file file.
Break *Address	Sets a breakpoint at the specified address. Generally used when there is no source code.
Break line-number ifcondition	If the condition is met, set the breakpoint at the specified location.
Break Line threadthread-number	Interrupts in the specified thread. Use info threads to display the thread number.
Tbreak	Sets a temporary breakpoint. Breakpoints are deleted after a break.
Watch Condition	Sets the observer point when the condition is met.
Clear Clear func Clear Nth	Clears the breakpoint at the function func . Clears the breakpoint at line Nth .
Delete D	Delete all breakpoints or observer points.
Delete Breakpoint-number Delete range	Deletes the specified breakpoint, the Observer point.
Disable breakpoint-number-or-range Enable Breakpoint-number-or-range	Do not delete the breakpoint, just set it to invalid, or valid. Example: Show Breakpoint: Info break Invalid setting: Disable 2-9
Enable onceBreakpoint-number	Sets the specified breakpoint to be valid, which is not valid when the breakpoint is reached.
Enable del Breakpoint-number	Sets the specified breakpoint to be valid and removes it when the breakpoint is reached.
Finish	Continue execution to the end of the function.
Line execution
Step S Step number-of-steps-to-perform	The execution of the next line of code goes inside the function.
Next N Next number	Executes the next line of code. But it doesn't go inside the function.
Until Until line-number Until line-number ifcondition	Continue running until you reach the specified line number, or function, address, and so on.
Return return expression	POPs the selected stack frame. If the parameter is specified later, the value of the expression is returned.
Stepi Si Nexti Ni	Executes the next assembly/CPU directive.
Info signals Info handle Handle signal-nameoption	When the signal is received, the following actions are performed: Nostop (do not stop program), Stop (Stop program execution), print (display signal), noprint (not shown), Pass/noignore (allows the program to process the signal), nopass/ Ignore (do not allow the program to accept the signal)
where	Displays the current line number and the function in which it is located.
Program Stack
BackTrace Bt BT inner-function-nesting-depth BT-outer-function-nesting-depth	Displays the current stack's trace, the current function.
BackTrace full	Prints the values of all local variables.
Frame Number F number	Selects the specified stack frame.
Up number Down number	Moves the specified number of stack frames up or down.
Info Frame Addr	Describes the selected stack frame.
Info args Info All-reg Info locals Info catch	Displays the parameters of the selected stack frame, local variables, exception handling functions. All-reg also lists floating-point registers.
Source Code
List L List Line-number List function List- List start#,end# List filename:function	List the corresponding source code.
Set Listsize Count Show Listsize	Sets the number of lines when the list command prints the source code.
Directory Directory-name Dir directory-name Show directories	Adds the specified directory before the source code path.
Directory	When no parameters are followed, clear the source code directory.
Examine Variables
Print variable P Variable P file::variable P 'file'::variable	Prints the value of the specified variable.
P *Array-var@length	Prints the first length entry in the Arrary-var .
p/x var	The integer variable varis printed in hexadecimal.
P/d var	The variable var is printed as a signed integer.
P/u var	The variable var is printed as an unsigned integer.
p/o var	The variable var is printed as an octal number.
p/t var x/b Address x/b &Variable	Prints the value of the var variable in integer binary form.
P/C Variable	When characters are printed.
p/f Variable	Print variable varin floating-point format.
P/A Variable	Prints the address in hexadecimal form.
x/w Address X/4B &Variable	Prints the specified address in a four-byte set of ways.
Call expression	Similar to print, but void is not printed.
Disassem Addr	The instructions in the specified address are disassembled.
Controlling GDB
Set gdb-option value	Sets the options for GDB.
Set Print array on Set Print array off Show Print Array	Prints an array in readable form. The default is off.
Set Print array-indexes on Set Print array-indexes off Show Print Array-indexes	Prints the subscript of an array element. The default is off.
Set Print pretty on Set print pretty off Show Print Pretty	Formats the output of the C-struct body.
Set Print Union on Set Print union off Show Print Union	Print a union in C. The default is on.
Set Print Demangle on Set Print Demangle off Show Print Demangle	Controls the printing of names in C + +. The default is on.
Working Files
Info files Info share	Lists the current files, shared libraries.
File file	Take file as a debugging program. If no parameters are specified, discard.
Core file	Take file as a core file. If no parameter is specified, it is discarded.
exec file	Consider file as the executing procedure. If no parameter is specified, it is discarded.
Symbol file	Reads the symbol table from file . If no parameter is specified, it is discarded.
Load file	Dynamically chain into the file and read its symbol table.
Path directory	Add directory directories to the path of the search executable and symbol files.
Start and Stop
Run R Run command-line-arguments Run < infile > outfile	Execute the program from the beginning, and also allow redirection.
Continue C	Resumes execution until the next breakpoint or observer point.
Continue Number	Continues execution, but ignores the current breakpoint number times. Useful when breakpoints are in a loop.
Kill	Stop program execution.
Quit Q	Exit the GDB debugger.

GDB Operation Tips

L need to add "-g" to GCC when compiling the executable so that it will add additional debugging information to the generated executable file.

L do not use the compiler's optimization options, such as: "-O", "-o2". Because the compiler will change the program flow for optimization, which is not conducive to debugging.

L Execute shell commands in GDB: Shell command

The GDB command can be used to complete the TAB key. Press the TAB key two times to see all possible matches.

L GDB command abbreviation: For example, the BRE in the info bre is equivalent to breakpoints.

GDB's operation in Emacs:

Emacs Key	Action
M-x GDB	Switch to GDB mode.
C-h m	Displays the GDB pattern introduction information.
M-s	is equivalent to the step command in GDB.
M-n	is equivalent to the next command in GDB.
M-i	Equivalent to the Stepi command in GDB.
C-c c-f	Equivalent to the finish command in GDB.
M-c	Equivalent to the Continue command in GDB.
M-u	is equivalent to the UP command in GDB.
M-d	is equivalent to the down command in GDB.

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GDB debug Manual [Go]