TranslateProject/sources/tech/20210107 A hands-on tutorial for using the GNU Project Debugger.md

[#]: collector: (lujun9972)
[#]: translator: ( )
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (A hands-on tutorial for using the GNU Project Debugger)
[#]: via: (https://opensource.com/article/21/1/gnu-project-debugger)
[#]: author: (Stephan Avenwedde https://opensource.com/users/hansic99)

A hands-on tutorial for using the GNU Project Debugger
======
The GNU Project Debugger is a powerful tool for finding bugs in
programs.
![magnifying glass on computer screen, finding a bug in the code][1]

If you're a programmer and you want to put a certain functionality in your software, you start by thinking of ways to implement it—such as writing a method, defining a class, or creating new data types. Then you write the implementation in a language that the compiler or interpreter can understand. But what if the compiler or interpreter does not understand the instructions as you had them in mind, even though you're sure you did everything right? What if the software works fine most of the time but causes bugs in certain circumstances? In these cases, you have to know how to use a debugger correctly to find the source of your troubles.

The GNU Project Debugger ([GDB][2]) is a powerful tool for finding bugs in programs. It helps you uncover the reason for an error or crash by tracking what is going on inside the program during execution.

This article is a hands-on tutorial on basic GDB usage. To follow along with the examples, open the command line and clone this repository:


```
`git clone https://github.com/hANSIc99/core_dump_example.git`
```

### Shortcuts

Every command in GDB can be shortened. For example, `info break`, which shows the set breakpoints, can be shortened to `i break`. You might see those abbreviations elsewhere, but in this article, I will write out the entire command so that it is clear which function is used.

### Command-line parameters

You can attach GDB to every executable. Navigate to the repository you cloned, and compile it by running `make`. You should now have an executable called **coredump**. (See my article on [_Creating and debugging Linux dump files_][3] for more information..

To attach GDB to the executable, type: `gdb coredump`.

Your output should look like this:

![gdb coredump output][4]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

It says no debugging symbols were found.

Debugging information is part of the object file (the executable) and includes data types, function signatures, and the relationship between the source code and the opcode. At this point, you have two options:

  * Continue debugging the assembly (see "[Debug without symbols][6]" below)
  * Compile with debug information using the information in the next section



### Compile with debug information

To include debug information in the binary file, you have to recompile it. Open the **Makefile** and remove the hashtag (`#`) from line 9:


```
`CFLAGS =-Wall -Werror -std=c++11 -g`
```

The `g` option tells the compiler to include the debug information. Run `make clean` followed by `make` and invoke GDB again. You should get this output and can start debugging the code:

![GDB output with symbols][7]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The additional debugging information will increase the size of the executable. In this case, it increases the executable by 2.5 times (from 26,088 byte to 65,480 byte).

Start the program with the `-c1` switch by typing `run -c1`. The program will start and crash when it reaches `State_4`:

![gdb output crash on c1 switch][8]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

You can retrieve additional information about the program. The command `info source` provides information about the current file:

![gdb info source output][9]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

  * 101 lines
  * Language: C++
  * Compiler (version, tuning, architecture, debug flag, language standard)
  * Debugging format: [DWARF 2][10]
  * No preprocessor macro information available (when compiled with GCC, macros are available only when [compiled with the `-g3` flag][11]).



The command `info shared` prints a list of dynamic libraries with their addresses in the virtual address space that was loaded on startup so that the program will execute:

![gdb info shared output][12]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

If you want to learn about library handling in Linux, see my article [_How to handle dynamic and static libraries in Linux_][13].

### Debug the program

You may have noticed that you can start the program inside GDB with the `run` command. The `run` command accepts command-line arguments like you would use to start the program from the console. The `-c1` switch will cause the program to crash on stage 4. To run the program from the beginning, you don't have to quit GDB; simply use the `run` command again. Without the `-c1` switch, the program executes an infinite loop. You would have to stop it with **Ctrl+C**.

![gdb output stopped by sigint][14]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

You can also execute a program step by step. In C/C++, the entry point is the `main` function. Use the command `list main` to open the part of the source code that shows the `main` function:

![gdb output list main][15]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The `main` function is on line 33, so add a breakpoint there by typing `break 33`:

![gdb output breakpoint added][16]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

Run the program by typing `run`. As expected, the program stops at the `main` function. Type `layout src` to show the source code in parallel:

![gdb output break at main][17]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

You are now in GDB's text user interface (TUI) mode. Use the Up and Down arrow keys to scroll through the source code.

GDB highlights the line to be executed. By typing `next` (n), you can execute the commands line by line. GBD executes the last command if you don't specify a new one. To step through the code, just hit the **Enter** key.

From time to time, you will notice that TUI's output gets a bit corrupted:

![gdb output corrupted][18]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

If this happens, press **Ctrl+L** to reset the screen.

Use **Ctrl+X+A** to enter and leave TUI mode at will. You can find [other key bindings][19] in the manual.

To quit GDB, simply type `quit`.

### Watchpoints

The heart of this example program consists of a state machine running in an infinite loop. The variable `n_state` is a simple enum that determines the current state:


```
while(true){
        switch(n_state){
        case State_1:
                std::cout << "State_1 reached" << std::flush;
                n_state = State_2;
                break;
        case State_2:
                std::cout << "State_2 reached" << std::flush;
                n_state = State_3;
                break;
       
        (.....)
       
        }
}
```

You want to stop the program when `n_state` is set to the value `State_5`. To do so, stop the program at the `main` function and set a watchpoint for `n_state`:


```
`watch n_state == State_5`
```

Setting watchpoints with the variable name works only if the desired variable is available in the current context.

When you continue the program's execution by typing `continue`, you should get output like:

![gdb output stop on watchpoint_1][20]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

If you continue the execution, GDB will stop when the watchpoint expression evaluates to `false`:

![gdb output stop on watchpoint_2][21]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

You can specify watchpoints for general value changes, specific values, and read or write access.

### Altering breakpoints and watchpoints

Type `info watchpoints` to print a list of previously set watchpoints:

![gdb output info watchpoints][22]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

#### Delete breakpoints and watchpoints

As you can see, watchpoints are numbers. To delete a specific watchpoint, type `delete` followed by the number of the watchpoint. For example, my watchpoint has the number 2; to remove this watchpoint, enter `delete 2`.

_Caution:_ If you use `delete` without specifying a number, _all_ watchpoints and breakpoints will be deleted.

The same applies to breakpoints. In the screenshot below, I added several breakpoints and printed a list of them by typing `info breakpoint`:

![gdb output info breakpoints][23]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

To remove a single breakpoint, type `delete` followed by its number. Alternatively, you can remove a breakpoint by specifying its line number. For example, the command `clear 78` will remove breakpoint number 7, which is set on line 78.

#### Disable or enable breakpoints and watchpoints

Instead of removing a breakpoint or watchpoint, you can disable it by typing `disable` followed by its number. In the following, breakpoints 3 and 4 are disabled and are marked with a minus sign in the code window:

![disabled breakpoints][24]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

It is also possible to modify a range of breakpoints or watchpoints by typing something like `disable 2 - 4`. If you want to reactivate the points, type `enable` followed by their numbers.

### Conditional breakpoints

First, remove all breakpoints and watchpoints by typing `delete`. You still want the program to stop at the `main` function, but instead of specifying a line number, add a breakpoint by naming the function directly. Type `break main` to add a breakpoint at the `main` function.

Type `run` to start the execution from the beginning, and the program will stop at the `main` function.

The `main` function includes the variable `n_state_3_count`, which is incremented when the state machine hits state 3.

To add a conditional breakpoint based on the value of `n_state_3_count` type:


```
`break 54 if n_state_3_count == 3`
```

![Set conditional breakpoint][25]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

Continue the execution. The program will execute the state machine three times before it stops at line 54. To check the value of `n_state_3_count`, type:


```
`print n_state_3_count`
```

![print variable][26]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

#### Make breakpoints conditional

It is also possible to make an existing breakpoint conditional. Remove the recently added breakpoint with `clear 54`, and add a simple breakpoint by typing `break 54`. You can make this breakpoint conditional by typing:


```
`condition 3 n_state_3_count == 9`
```

The `3` refers to the breakpoint number.

![modify breakpoint][27]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

#### Set breakpoints in other source files

If you have a program that consists of several source files, you can set breakpoints by specifying the file name before the line number, e.g., `break main.cpp:54`.

#### Catchpoints

In addition to breakpoints and watchpoints, you can also set catchpoints. Catchpoints apply to program events like performing syscalls, loading shared libraries, or raising exceptions.

To catch the `write` syscall, which is used to write to STDOUT, enter:


```
`catch syscall write`
```

![catch syscall write output][28]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

Each time the program writes to the console output, GDB will interrupt execution.

In the manual, you can find a whole chapter [covering break-, watch-, and catchpoints][29].

### Evaluate and manipulate symbols

Printing the values of variables is done with the `print` command. The general syntax is `print <expression> <value>`. The value of a variable can be modified by typing:


```
`set variable <variable-name> <new-value>.`
```

In the screenshot below, I gave the variable `n_state_3_count` the value _123_.

![print variable][30]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The `/x` expression prints the value in hexadecimal; with the `&` operator, you can print the address within the virtual address space.

If you are not sure of a certain symbol's data type, you can find it with `whatis`:

![whatis output][31]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

If you want to list all variables that are available in the scope of the `main` function, type `info scope main`:

![info scope main output][32]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The `DW_OP_fbreg` values refer to the stack offset based on the current subroutine.

Alternatively, if you are already inside a function and want to list all variables on the current stack frame, you can use `info locals`:

![info locals output][33]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

Check the manual to learn more about [examining symbols][34].

### Attach to a running process

The command `gdb attach <process-id>` allows you to attach to an already running process by specifying the process ID (PID). Luckily, the `coredump` program prints its current PID to the screen, so you don't have to manually find it with [ps][35] or [top][36].

Start an instance of the coredump application:


```
`./coredump`
```

![coredump application][37]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The operating system gives the PID `2849`. Open a separate console window, move to the coredump application's source directory, and attach GDB:


```
`gdb attach 2849`
```

![attach GDB to coredump][38]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

GDB immediately stops the execution when you attach it. Type `layout src` and `backtrace` to examine the call stack:

![layout src and backtrace output][39]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The output shows the process interrupted while executing the `std::this_thread::sleep_for<...>(...)` function that was called in line 92 of `main.cpp`.

As soon as you quit GDB, the process will continue running.

You can find more information about [attaching to a running process][40] in the GDB manual.

#### Move through the stack

Return to the program by using `up` two times to move up in the stack to `main.cpp`:

![moving up the stack to main.cpp][41]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

Usually, the compiler will create a subroutine for each function or method. Each subroutine has its own stack frame, so moving upwards in the stackframe means moving upwards in the callstack.

You can find out more about [stack evaluation][42] in the manual.

#### Specify the source files

When attaching to an already running process, GDB will look for the source files in the current working directory. Alternatively, you can specify the source directories manually with the [`directory` command][43].

### Evaluate dump files

Read [_Creating and debugging Linux dump files_][3] for information about this topic.

TL;DR:

  1. I assume you're working with a recent version of Fedora

  2. Invoke coredump with the c1 switch: `coredump -c1`

![Crash meme][44]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

  3. Load the latest dumpfile with GDB: `coredumpctl debug`

  4. Open TUI mode and enter `layout src`




![coredump output][45]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The output of `backtrace` shows that the crash happened five stack frames away from `main.cpp`. Enter to jump directly to the faulty line of code in `main.cpp`:

![up 5 output][46]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

A look at the source code shows that the program tried to free a pointer that was not returned by a memory management function. This results in undefined behavior and caused the `SIGABRT`.

### Debug without symbols

If there are no sources available, things get very hard. I had my first experience with this when trying to solve reverse-engineering challenges. It is also useful to have some knowledge of [assembly language][47].

Check out how it works with this example.

Go to the source directory, open the **Makefile**, and edit line 9 like this:


```
`CFLAGS =-Wall -Werror -std=c++11 #-g`
```

To recompile the program, run `make clean` followed by `make` and start GDB. The program no longer has any debugging symbols to lead the way through the source code.

![no debugging symbols][48]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The command `info file` reveals the memory areas and entry point of the binary:

![info file output][49]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The entry point corresponds with the beginning of the `.text` area, which contains the actual opcode. To add a breakpoint at the entry point, type `break *0x401110` then start execution by typing `run`:

![breakpoint at the entry point][50]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

To set up a breakpoint at a certain address, specify it with the dereferencing operator `*`.

#### Choose the disassembler flavor

Before digging deeper into assembly, you can choose which [assembly flavor][51] to use. GDB's default is AT&amp;T, but I prefer the Intel syntax. Change it with:


```
`set disassembly-flavor intel`
```

![changing assembly flavor][52]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

Now open the assembly and register the window by typing `layout asm` and `layout reg`. You should now see output like this:

![layout asm and layout reg output][53]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

#### Save configuration files

Although you have already entered many commands, you haven't actually started debugging. If you are heavily debugging an application or trying to solve a reverse-engineering challenge, it can be useful to save your GDB-specific settings in a file.

The [config file `gdbinit`][54] in this project's GitHub repository contains the recently used commands:


```
set disassembly-flavor intel
set write on
break *0x401110
run -c2
layout asm
layout reg
```

The `set write on` command enables you to modify the binary during execution.

Quit GDB and reopen it with the configuration file: `gdb -x gdbinit coredump`.

#### Read instructions

With the `c2` switch applied, the program will crash. The program stops at the entry function, so you have to write `continue` to proceed with execution:

![continuing execution after crash][55]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

The `idiv` instruction performs an integer division with the dividend in the `RAX` register and the divisor specified as an argument. The quotient is loaded into the `RAX` register, and the remainder is loaded into `RDX`.

From the register overview, you can see the `RAX` contains _5_, so you have to find out which value is stored on the stack at position `RBP-0x4`.

#### Read memory

To read raw memory content, you must specify a few more parameters than for reading symbols. When you scroll up a bit in the assembly output, you can see the division of the stack:

![stack division output][56]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

You're most interested in the value of `rbp-0x4` because this is the position where the argument for `idiv` is stored. From the screenshot, you can see that the next variable is located at `rbp-0x8`, so the variable at `rbp-0x4` is 4 bytes wide.

In GDB, you can use the `x` command to _examine_ any memory content:

> `x/` &lt; optional parameter `n` `f` `u` &gt; &lt; memory address `addr` &gt;

Optional parameters:

  * `n`: Repeat count (default: 1) refers to the unit size
  * `f`: Format specifier, like in [printf][57]
  * `u`: Unit size
    * `b`: bytes
    * `h`: half words (2 bytes)
    * `w`: word (4 bytes)(default)
    * `g`: giant word (8 bytes)



To print out the value at `rbp-0x4`, type `x/u $rbp-4`:

![print value][58]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

If you keep this pattern in mind, it's straightforward to examine the memory. Check the [examining memory][59] section in the manual.

#### Manipulate the assembly

The arithmetic exception happened in the subroutine `zeroDivide()`. When you scroll a bit upward with the Up arrow key, you can find this pattern:


```
0x401211 &lt;_Z10zeroDividev&gt;              push   rbp
0x401212 &lt;_Z10zeroDividev+1&gt;            mov    rbp,rsp  
```

This is called the [function prologue][60]:

  1. The base pointer (`rbp`) of the calling function is stored on the stack
  2. The value of the stack pointer (`rsp`) is loaded to the base pointer (`rbp`)



Skip this subroutine completely. You can check the call stack with `backtrace`. You are only one stack frame ahead of your `main` function, so you can go back to `main` with a single `up`:

![Callstack assembly][61]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

In your `main` function, you can find this pattern:


```
0x401431 &lt;main+497&gt;     cmp    BYTE PTR [rbp-0x12],0x0
0x401435 &lt;main+501&gt;     je     0x40145f &lt;main+543&gt;
0x401437 &lt;main+503&gt;     call   0x401211&lt;_Z10zeroDividev&gt;
```

The subroutine `zeroDivide()` is entered only when `jump equal (je)` evaluates to `true`. You can easily replace this with a `jump-not-equal (jne)` instruction, which has the opcode `0x75` (provided you are on an x86/64 architecture; the opcodes are different on other architectures). Restart the program by typing `run`. When the program stops at the entry function, manipulate the opcode by typing:


```
`set *(unsigned char*)0x401435 = 0x75`
```

Finally, type `continue`. The program will skip the subroutine `zeroDivide()` and won't crash anymore.

### Conclusion

You can find GDB working in the background in many integrated development environments (IDEs), including Qt Creator and the [Native Debug][62] extension for VSCodium.

![GDB in VSCodium][63]

(Stephan Avenwedde, [CC BY-SA 4.0][5])

It's useful to know how to leverage GDB's functionality. Usually, not all of GDB's functions can be used from the IDE, so you benefit from having experience using GDB from the command line.

--------------------------------------------------------------------------------

via: https://opensource.com/article/21/1/gnu-project-debugger

作者：[Stephan Avenwedde][a]
选题：[lujun9972][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)

本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出

[a]: https://opensource.com/users/hansic99
[b]: https://github.com/lujun9972
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/mistake_bug_fix_find_error.png?itok=PZaz3dga (magnifying glass on computer screen, finding a bug in the code)
[2]: https://www.gnu.org/software/gdb/
[3]: https://opensource.com/article/20/8/linux-dump
[4]: https://opensource.com/sites/default/files/uploads/gdb_output_no_dbg_symbols.png (gdb coredump output)
[5]: https://creativecommons.org/licenses/by-sa/4.0/
[6]: tmp.2p0XrqmAS5#without_symbols
[7]: https://opensource.com/sites/default/files/uploads/gdb_output_with_symbols.png (GDB output with symbols)
[8]: https://opensource.com/sites/default/files/uploads/gdb_output_crash_on_c1_switch.png (gdb output crash on c1 switch)
[9]: https://opensource.com/sites/default/files/uploads/gdb_output_info_source.png (gdb info source output)
[10]: http://dwarfstd.org/
[11]: https://sourceware.org/gdb/current/onlinedocs/gdb/Compilation.html#Compilation
[12]: https://opensource.com/sites/default/files/uploads/gdb_output_info_shared.png (gdb info shared output)
[13]: https://opensource.com/article/20/6/linux-libraries
[14]: https://opensource.com/sites/default/files/uploads/gdb_output_stopped_by_sigint.png (gdb output stopped by sigint)
[15]: https://opensource.com/sites/default/files/uploads/gdb_output_list_main.png (gdb output list main)
[16]: https://opensource.com/sites/default/files/uploads/gdb_output_breakpoint_added.png (gdb output breakpoint added)
[17]: https://opensource.com/sites/default/files/uploads/gdb_output_break_at_main.png (gdb output break at main)
[18]: https://opensource.com/sites/default/files/images/gdb_output_screen_corrupted.png (gdb output corrupted)
[19]: https://sourceware.org/gdb/onlinedocs/gdb/TUI-Keys.html#TUI-Keys
[20]: https://opensource.com/sites/default/files/uploads/gdb_output_stop_on_watchpoint_1.png (gdb output stop on watchpoint_1)
[21]: https://opensource.com/sites/default/files/uploads/gdb_output_stop_on_watchpoint_2.png (gdb output stop on watchpoint_2)
[22]: https://opensource.com/sites/default/files/uploads/gdb_output_info_watchpoints.png (gdb output info watchpoints)
[23]: https://opensource.com/sites/default/files/uploads/gdb_output_info_breakpoints.png (gdb output info breakpoints)
[24]: https://opensource.com/sites/default/files/uploads/gdb_output_disabled_breakpoints.png (disabled breakpoints)
[25]: https://opensource.com/sites/default/files/uploads/gdb_output_set_conditional_breakpoint.png (Set conditional breakpoint)
[26]: https://opensource.com/sites/default/files/uploads/gdb_output_print_variable.png (print variable)
[27]: https://opensource.com/sites/default/files/uploads/gdb_output_modify_breakpoint.png (modify breakpoint)
[28]: https://opensource.com/sites/default/files/uploads/gdb_output_syscall_catch.png (catch syscall write output)
[29]: https://sourceware.org/gdb/current/onlinedocs/gdb/Breakpoints.html#Breakpoints
[30]: https://opensource.com/sites/default/files/uploads/gdb_output_print_and_modify.png (print variable)
[31]: https://opensource.com/sites/default/files/uploads/gdb_output_whatis.png (whatis output)
[32]: https://opensource.com/sites/default/files/uploads/gdb_output_info_scope_main.png (info scope main output)
[33]: https://opensource.com/sites/default/files/uploads/gdb_output_info_locals_main.png (info locals output)
[34]: https://sourceware.org/gdb/current/onlinedocs/gdb/Symbols.html
[35]: https://man7.org/linux/man-pages/man1/ps.1.html
[36]: https://man7.org/linux/man-pages/man1/top.1.html
[37]: https://opensource.com/sites/default/files/uploads/coredump_running.png (coredump application)
[38]: https://opensource.com/sites/default/files/uploads/gdb_output_attaching_to_process.png (attach GDB to coredump)
[39]: https://opensource.com/sites/default/files/uploads/gdb_output_backtrace.png (layout src and backtrace output)
[40]: https://sourceware.org/gdb/current/onlinedocs/gdb/Attach.html#Attach
[41]: https://opensource.com/sites/default/files/uploads/gdb_output_stackframe_up.png (moving up the stack to main.cpp)
[42]: https://sourceware.org/gdb/current/onlinedocs/gdb/Stack.html#Stack
[43]: https://ftp.gnu.org/old-gnu/Manuals/gdb/html_node/gdb_48.html#SEC49
[44]: https://opensource.com/sites/default/files/uploads/crash.png (Crash meme)
[45]: https://opensource.com/sites/default/files/uploads/gdb_output_coredump.png (coredump output)
[46]: https://opensource.com/sites/default/files/uploads/gdb_output_up_five.png (up 5 output)
[47]: https://en.wikipedia.org/wiki/Assembly_language
[48]: https://opensource.com/sites/default/files/uploads/gdb_output_no_debugging_symbols.png (no debugging symbols)
[49]: https://opensource.com/sites/default/files/uploads/gdb_output_info_file.png (info file output)
[50]: https://opensource.com/sites/default/files/uploads/gdb_output_break_at_start.png (breakpoint at the entry point)
[51]: https://en.wikipedia.org/wiki/X86_assembly_language#Syntax
[52]: https://opensource.com/sites/default/files/uploads/gdb_output_disassembly_flavor.png (changing assembly flavor)
[53]: https://opensource.com/sites/default/files/uploads/gdb_output_layout_reg_asm.png (layout asm and layout reg output)
[54]: https://github.com/hANSIc99/core_dump_example/blob/master/gdbinit
[55]: https://opensource.com/sites/default/files/uploads/gdb_output_asm_div_zero.png (continuing execution after crash)
[56]: https://opensource.com/sites/default/files/uploads/gdb_output_stack_division.png (stack division output)
[57]: https://en.wikipedia.org/wiki/Printf_format_string#Type_field
[58]: https://opensource.com/sites/default/files/uploads/gdb_output_examine_1.png (print value)
[59]: https://sourceware.org/gdb/current/onlinedocs/gdb/Memory.html
[60]: https://en.wikipedia.org/wiki/Function_prologue
[61]: https://opensource.com/sites/default/files/uploads/gdb_output_callstack_assembly_0.png (Callstack assembly)
[62]: https://github.com/WebFreak001/code-debug
[63]: https://opensource.com/sites/default/files/uploads/vs_codium_native_debug.png (GDB in VSCodium)