Add gdb-cheat-sheet

linux/gdb-cheat-sheet.md

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+# GDB command cheat sheet
+
+**Note**: The abbreviation of command is surrounded by round brackets.
+
+## Start & Quit
+
+### Start gdb and program
+- **gdb** *program*
+  - Start gdb to debug a program.
+- **gdb** *program* *corefile*
+  - Start gdb and open a coredump file.
+- **gdb** --pid *pid*
+
+  **attach** *pid* 
+  - attach to a process
+- **run** (r)
+  - run the program 
+- **gdb** *program* --args *arg1* *arg2* 
+
+  **run** *arg1* *arg2*
+  - run the program with arguments
+
+### Kill and quit
+- **kill**
+  - Kill the running program.
+
+
+- **quit** (q) 
+
+  Ctrl + d
+  - exit gdb
+
+
+## Show information
+### info
+Generic command for showing things about the program being debugged.
+- **info** args
+  - Print the arguments to the function of the current stack frame 
+- **info** locals
+  - Print the local variables in the currently selected stack frame.
+- **info** breakpoints (info b)
+  - Print informations about the breakpoints and watchpoints.
+- **info** watchpoints *watchpoint*
+  - Print status of specified watchpoints (all watchpoints if no argument);
+- **info** threads
+  - Display currently known threads
+- **info** stack (info s)
+  - Print the backtrace of the stack.
+- **info** frame (info f)
+  - Print all about selected stack frame.
+- **info** source
+  - Print information about the current source file
+- **info** types
+  - Print all type names.
+- **info** variables
+  - Print all global and static variable names. 
+
+### show
+Generic command for showing things about the debugger.
+- **show** directories
+  - Print all directories in which GDB searches for source files.
+- **show** listsize
+  - Print how many are shown in the "list" command.
+
+## Variables and memory
+### format specifier
+- o - octal
+- x - hexadecimal
+- u - unsigned decimal
+- t - binary
+- f - floating point
+- a - address
+- c - char
+- s - string
+### size modifier
+- b - byte
+- h - halfword (16-bit value)
+- w - word (32-bit value)
+- g - giant word (64-bit value)
+### print
+- **print** *expression*
+  - Prints the value of a given expression.
+- **print** $*i*
+  - Repeat the output produced by its i-th invocation.
+- **print** {*Type*}*Address*
+
+  **print** \*(*PointerType*)*Address*
+  - Print the content of specified address as type.
+- **print** *FirstElement*@*ElementCount*
+  - Interpret the FirstElement expression as an array of ElementCount sequential elements.
+- **print** /*Format* *Expression*
+  - Overriding the output format used by the command.
+### display
+Just like print, but will print each time GDB stops at a breakpoint or after a step.
+- **display** *Expression*
+- **x** /*Format* *Expression*
+- **display**
+  - Show the current list expressions enabled for auto-displaying.
+- **enable** display *display*
+
+  **disable** display *display*
+  - Enable or disable the display with the given number.
+
+## Breakpoint
+### setting breakpoints
+- **break** *function*
+- **break** *line*
+- **break** *filename*:*function*
+- **break** *filename*:*line*
+- **delete** *breakpoint*
+### removing breakpoints
+- **clear**
+  - Delete all breakpoints.
+- **enable** *breakpoint*
+- **disable** *breakpoint*
+### condition
+
+## Watchpoint
+Similar usage to breakpoints.
+- **watch** *expression*
+
+## Stepping
+- **step** *count* (s)
+  - Go to next line and step into functions.
+  - If count is specified, gdb will repeat this for count times.
+- **next** *count* (n)
+  - Go to next line without stepping in.
+- **continue** *ignore-count* (c)
+  - Continue the program until next breakpoint is hit.
+  - If ignore-count is specified, next ignore-count breakpoint will be ignored.
+- **finish**
+  - Continue the function until current function is finished.
+  - Will print the return value.
+
+## Stack 
+- **backtrace** *n*
+  **where** *n*
+  - Print stack information.
+  - If n is set, positive n means showing top n stack frames, negative n means showing bottom n stack frames.
+- **set backtrace limit** *n*
+  - Set max frame number when using backtrace.
+- **frame** *n* (f *n*)
+
+  **frame** *addr* 
+  - Select the stack frame to operate on by frame number or pc address.
+
+
+## Multithreads
+- **thread** *thread*
+  - Choose thread to operate on.
+- **thread** apply *thread-id-list* *command*
+
+  **thread** apply all *command*
+  - Execute command on all or specified list of threads.
+- **set scheduler-locking** *mode*
+  - Mode can be:
+    - **off**: There is no locking and any thread may run at any time.
+    - **on**: Only the current thread may run when the inferior is resumed
+    - **step**: It prevents other threads from preempting the current thread while you are stepping, so that the focus of debugging does not change unexpectedly. Other threads never get a chance to run when you step, and they are completely free to run when you use commands like ‘continue’, ‘until’, or ‘finish’.
+- **show scheduler-locking**
+  - Display the current scheduler locking mode.
+
+
+
+## Reference
+
+You may find more helpful usages in these links.
+
+- [GDB cheatsheet](https://darkdust.net/files/GDB%20Cheat%20Sheet.pdf)
+- [VisualGDB](https://visualgdb.com/gdbreference/commands/)
+- [Debugging with GDB](https://sourceware.org/gdb/current/onlinedocs/gdb/)