gdb - What is the difference between dprintf vs break + commands + continue? -

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for example:

dprintf main,"hello\n" run

generates same output as:

break main commands   silent   printf "hello\n"   continue end run

is there significant advantage using dprintf on commands, e.g. considerably faster (if why?), or has different functionality?

or convenience command?

source

in 7.9.1 source, breakpoint.c:dprintf_command, defines dprintf, calls create_breakpoint break_command calls, both seem use same underlying mechanism.

the main difference dprintf passes dprintf_breakpoint_ops structure, has different callbacks , gets initialized @ initialize_breakpoint_ops.

dprintf stores list of command strings of commands command, depending on settings. are:

  • set @ update_dprintf_command_list
  • which gets called on after type == bp_dprintf check inside init_breakpoint_sal
  • which gets called create_breakpoint.

when breakpoint reached:

  • bpstat_stop_status gets called , invokes b->ops->after_condition_true (bs); breakpoint reached
  • after_condition_true dprintf dprintf_after_condition_true
  • bpstat_do_actions_1 runs commands

there 2 main differences.

first, dprintf has additional output modes can used make work in other ways. see help set dprintf-channel, or manual, more information. think these modes reason dprintf added separate entity; though @ same time specialized , unlikely of general interest.

more usefully, though, dprintf doesn't interfere next. if write breakpoint , use commands, , next on such breakpoint, gdb forget next , act if had typed continue. longstanding oddity in gdb scripting language. dprintf doesn't suffer problem. (if need similar functionality ordinary breakpoint, can python.)


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