This patch adds conditional tracepoints.  Tracepoint conditions work by 
being compiled into agent expressions that actually evaluate on the spot 
in the target, rather than collecting blocks of trace data.  As usual 
for tracepoints, GDB proper doesn't have to do much, and most of the 
code here revolves around checking for the "ConditionalTracepoints" 
feature, so as to maintain compatibility with the two(?) existing 
tracepoint implementations out there.  As a bonus subpatch, I added 
bytecode generation for comparison operators, other boolean ops are 
coming later.  I tested by exercising with CodeSourcery's target agent, 
in the absence of anything usable in the GDB testsuite.

Stan

2009-06-26  Stan Shebs  <stan@codesourcery.com>

    Conditional tracepoints.
    * ax-gdb.h (gen_eval_for_expr): Declare.
    * ax-gdb.c (gen_expr): Generate bytecodes for BINOP_EQUAL
    and other comparisons.
    (gen_eval_for_expr): New function.
    (agent_eval_command): New maintenance command.
    (_initialize_ax_gdb): Define the command.
    * remote.c (struct remote_state): New field cond_tracepoints.
    (PACKET_ConditionalTracepoints): New packet config type.
    (remote_cond_tracepoint_feature): New function.
    (remote_protocol_features): Add ConditionalTracepoints.
    (remote_supports_cond_tracepoints): New function.
    (_initialize_remote): Add ConditionalTracepoints.
    * tracepoint.c (download_tracepoint): Add conditional.

==> doc/ChangeLog <==
2009-06-26  Stan Shebs  <stan@codesourcery.com>

    * gdb.texinfo (Tracepoint Conditions): New section.
    (General Query Packets): Describe ConditionalTracepoints.
    (Tracepoint Packets): Describe condition field.
    (Maintenance Commands): Describe maint agent-eval.

==> testsuite/ChangeLog <==
2009-06-26  Stan Shebs  <stan@codesourcery.com>

    * gdb.trace/tracecmd.exp: Add basic test of tracepoint conditions.