Figure 2.6 shows the high level sequence diagram for GDB in response to the break command. This example is for the case where the target of the break is a symbol (i.e. a function name) in the target executable.

Figure 2.6.  Sequence diagram for the GDB break command

Most of the action with breakpoints occurs when the program is set running, at which any active breakpoints are installed. However for any break command, the address for the break must be set up in the breakpoint data structure.

For symbolic addresses, the start of the function can be obtained from the line number information held for debugging purposes in the symbol table (known as symbol-and-line information, or SAL). For a function, this will yield the start address of the code. However the breakpoint must be set after the function prologue. gdbarch_skip_prolog is used to find that address in the code.