[PATCH] Dynamic printf for a target agent

[Stan Shebs <stanshebs at earthlink dot net>]

This patch extends dynamic printf to run on the target, using a 
debugging agent.  Among other things, this lets the user disconnect GDB 
from the target, and the prints continue to be active; so they are even 
more like printf calls that don't have to be compiled into the code.

The user interface simply consists of an additional dprintf style 
"agent", plus a disconnected-dprintf setshow to control the disconnected 
printing behavior.

To address some of the issues raised previously, I took the moderately 
drastic step of dismembering, uh, *refactoring* GDB's printf command, 
separating out the format string parsing into a common/ function.  So 
now the code parses the format string on the host side and uses that to 
create the correct list of agent expressions, then on the target side, 
GDBserver does the same exact same parsing and prints each expression 
result in the same way.  Although it's a messy cut, there's no 
user-visible behavior change, and no regressions from the testsuite.

This patch doesn't reflect the suggestion to special-case dprintf 
behavior instead of using a command list; I'll respond to that 
separately.  The patch does set up general infrastructure to run 
breakpoint commands on the target - that seems worth doing in any case, 
as it will offer the same advantages for multicore debugging as is the 
case for target-side breakpoint conditions.

Stan

2012-05-29  Stan Shebs <stan@codesourcery.com>

    Add target-side support for dynamic printf.
    * NEWS: Mention the additional style.
    * breakpoint.h (struct bp_target_info): New fields tcommands, persist.
    (struct bp_location): New field cmd_bytecode.
    * breakpoint.c: Include format.h.
    (disconnected_dprintf): New global.
    (parse_cmd_to_aexpr): New function.
    (build_target_command_list): New function.
    (insert_bp_location): Call it.
    (remove_breakpoints_pid): Skip dprintf breakpoints.
    (print_one_breakpoint_location): Ditto.
    (dprintf_style_agent): New global.
    (dprintf_style_enums): Add dprintf_style_agent.
    (update_dprintf_command_list): Add agent case.
    (agent_printf_command): New function.
    (_initialize_breakpoint): Add new commands.
    * common/ax.def (printf): New bytecode.
    * ax.h (ax_string): Declare.
    * ax-gdb.h (gen_printf): Declare.
    * ax-gdb.c: Include cli-utils.h, format.h.
    (gen_printf): New function.
    (maint_agent_print_command): New function.
    (_initialize_ax_gdb): Add maint agent-printf command.
    * ax-general.c (ax_string): New function.
    (ax_print): Add printf disassembly.
    * Makefile.in (SFILES): Add format.c
    (COMMON_OBS): Add format.o.
    * common/format.h: New file.
    * common/format.c: New file.
    * printcmd.c: Include format.h.
    (ui_printf): Call parse_format_string.
    * remote.c (remote_state): New field breakpoint_commands.
    (PACKET_BreakpointCommands): 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
    to_can_run_breakpoint_commands.
    (target_can_run_breakpoint_commands): New macro.
    * target.c (update_current_target): Handle
    to_can_run_breakpoint_commands.

    [gdbserver]
    * Makefile.in (WARN_CFLAGS_NO_FORMAT): Define.
    (ax.o): Add it to build rule.
    (ax-ipa.o): Ditto.
    (OBS): Add format.o.
    (IPA_OBS): Add format.o.
    * 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
    effect.
    * mem-break.h (any_persistent_commands): Declare.
    (add_breakpoint_commands): Declare.
    (gdb_no_commands_at_breakpoint): Declare.
    (run_breakpoint_commands): Declare.
    * 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.
    * linux-low.c (linux_wait_1): Test for and run breakpoint commands
    locally.
    * ax.c: Include format.h.
    (ax_printf): New function.
    (gdb_eval_agent_expr): Add printf opcode.

    [doc]
    * gdb.texinfo (Dynamic Printf): Mention agent style and
    disconnected dprintf.
    (Maintenance Commands): Describe maint agent-printf.
    (General Query Packets): Mention BreakpointCommands feature.
    (Packets): Document commands extension to Z0 packet.
    * agentexpr.texi (Bytecode Descriptions): Document printf
    bytecode.

    [testsuite]
    * gdb.base/dprintf.exp: Add agent style tests.

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