Editing GNU Debugger (section)

===Internals ===
GDB uses a system call named [[ptrace]] (the name is an abbreviation of "process trace") to observe and control the execution of another process, and examine and change the process' memory and registers.
{{aligned table|class=wikitable|cols=2|col1header=y|col1align=left|row1header=y
| Common gdb commands | Corresponding ptrace calls
| <syntaxhighlight lang="console" inline>(gdb) start</syntaxhighlight> | {{mono|PTRACE_TRACEME}} – makes parent a tracer (called by a tracee)

| <syntaxhighlight lang="console" inline>(gdb) attach PID</syntaxhighlight> | {{mono|PTRACE_ATTACH}} – attach to a running process
| <syntaxhighlight lang="console" inline>(gdb) stop</syntaxhighlight> | {{code|kill(child_pid, SIGSTOP)}} (or {{mono|PTRACE_INTERRUPT}})
| <syntaxhighlight lang="console" inline>(gdb) continue</syntaxhighlight> | {{mono|PTRACE_CONT}}
| <syntaxhighlight lang="console" inline>(gdb) info registers</syntaxhighlight> | {{mono|PTRACE_GET(FP)REGS(ET)}} and {{mono|PTRACE_SET(FP)REGS(ET)}}
| <syntaxhighlight lang="console" inline>(gdb) x</syntaxhighlight> | {{mono|PTRACE_PEEKTEXT}} and {{mono|PTRACE_POKETEXT}}
}}
A breakpoint is implemented by replacing an instruction at a given memory address with another special instruction. Executing breakpoint instruction causes SIGTRAP.