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[PATCH] dynamic printf

This patch implements a "dynamic printf", which is basically a breakpoint with a printf;continue as its command list - but with additional features that make it more interesting. First, there is an option to send the result to the inferior's output stream rather than to the GDB console; second, there is an option to do the printing in a remote agent/stub; and third, the agent version can continue printf'ing even after GDB detaches(!).

(For those who pay attention to the competitive landscape, this is an Ericsson-requested GDBification of a Wind River feature.)

The syntax of the command is

dprintf <location> <format>,<arg>,<arg>...

where the location is as for breakpoints, while the format and args are as for the printf command. So you could have something like

dprintf myfun "myfun args are %d,%d\n",arg1,arg2

A setshow variable dprintf-style controls whether the printing is done by GDB, the inferior, or by a remote agent, and another variable disconnected-dprintf controls persistence upon disconnection, similarly to disconnected tracing.

The patch itself is somewhat of a hack-n-slash through the middle of GDB, and there is much to critique. :-) Partly this is because I wanted to push through to a genuinely useful example of target-side breakpoint commands, rather than doing limited-functionality "commands" in the abstract. It also points up our continuing need for being able to define types of breakpoints by properties rather than adding enums... I borrowed some of Luis' target-side conditional code, and got some inspiration from Hui Zhu's previous try at a printf bytecode.

Anyway, without further ado, here's the patch itself. I've skipped the testsuite for now, as I expect everybody will want nontrivial modifications. :-)


2012-02-28 Stan Shebs <>

    Add dynamic printf.
    * breakpoint.h (enum bptype): New type bp_dprintf.
    (struct bp_target_info): New field commands and persist.
    (struct bp_location): New field cmd_bytecode.
    (struct breakpoint): New field extra_string.
    * breakpoint.c (dprintf_breakpoint_ops): New.
    (disconnected_dprintf): New global.
    (is_breakpoint): Add bp_dprintf.
    (parse_format_string): New function.
    (parse_cmd_to_aexpr): New function.
    (build_target_command_list): New function.
    (insert_bp_location): Call it.
    (remove_breakpoints_pid): Skip dprintf breakpoints.
    (bpstat_what): Add dprintf case.
    (bptype_string): Ditto.
    (print_one_breakpoint_location): Ditto.
    (init_bp_location): Ditto.
    (bkpt_print_mention): Ditto.
    (dprintf_style_enums): New array.
    (dprintf_style): New global.
    (glob_extra_string): New global.
    (init_breakpoint_sal): Handle extra string.
    (addr_string_to_sals): Ditto.
    (find_condition_and_thread): Add extra argument.
    (create_breakpoint): Save away additional text at end of command.
    (dprintf_command): New function.
    (_initialize_breakpoint): Add new commands.
    * common/ax.def (printf): New bytecode.
    * ax-gdb.c (gen_printf): New function.
    (agent_print_command): New function.
    (_initialize_ax_gdb): Add maint agent-printf command.
    * ax-gdb.h (gen_printf): Declare.
    * ax-general.c (ax_print): Add printf disassembly.
    * remote.c (remote_state) <cond_breakpoints>: New field.
    (PACKET_BreakpointCommandss): New enum.
    (remote_breakpoint_commands_feature): New function.
    (remote_protocol_features): Add new BreakpointCommands entry.
    (remote_can_run_breakpoint_commands): New function.
    (remote_add_target_side_commands): New function.
    (remote_insert_breakpoint): Call it.
    (remote_insert_hw_breakpoint): Ditto.
    (_initialize_remote): Add new packet configuration for
    target-side breakpoint commands.
    * target.h (struct target_ops): New field
    (target_can_run_breakpoint_commands): New macro.
    * target.c (update_current_target): Handle

    * server.c (handle_query): Claim support for breakpoint commands.
    (process_point_options): Add command case.
    (process_serial_event): Leave running if there are printfs in
    * mem-break.c (struct point_command_list): New struct.
    (struct breakpoint): New field command_list.
    (any_persistent_commands): New function.
    (add_commands_to_breakpoint): New function.
    (add_breakpoint_commands): New function.
    (gdb_no_commands_at_breakpoint): New function.
    (run_breakpoint_commands): New function.
    * mem-break.h (any_persistent_commands): Declare.
    (add_breakpoint_commands): Declare.
    (gdb_no_commands_at_breakpoint): Declare.
    (run_breakpoint_commands): Declare.
    * linux-low.c (linux_wait_1): Test for and run breakpoint commands
    * ax.c (gdb_eval_agent_expr): Add printf opcode.

    * gdb.texinfo (Dynamic Printf): New subsection.

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