[PATCH v2] Shorter fast tracepoints

[Stan Shebs]

Here is a more-polished version of the shorter fast tracepoints patch.  
It incorporates EliZ's feedback on the documentation, describing the 
arcana in some more detail.

It also adds a generic fast tracepoint test case, plus Yao-inspired asm 
hackery to include an actual 4-byte instruction to be the tracepoint 
location.  There is one downside to the test case, in that the number of 
passes will vary depending on the setting of mmap_min_addr - adding 
artificial xfails is a possibility, although this test can only run on 
32-bit x86 Linux with GDBserver, so you have to work just to get to the 
test in the first place. :-)

I plan to commit this if there are no objections.

Stan
stan@codesourcery.com


2011-11-10  Stan Shebs <stan@codesourcery.com>
         Kwok Cheung Yeung <kcy@codesourcery.com>

     * NEWS: Document shorter fast tracepoints and qTMinFTPILen packet.
     * i386-tdep.c (i386_fast_tracepoint_valid_at): Query target for
     the minimum instruction size for fast tracepoints.
     * target.h (struct target_ops): Add new method
     to_get_min_fast_tracepoint_insn_len.
     (target_get_min_fast_tracepoint_insn_len): New.
     * target.c (update_current_target): Set up new target operation.
     * remote.c (remote_write_bytes_aux): Fix typo.
     (remote_download_tracepoint): Revert to regular tracepoint if a
     fast tracepoint is placed on an instruction that is too short.
     (remote_get_min_fast_tracepoint_insn_len): New.
     (init_remote_ops): Initialize new field.

     [gdbserver]
     * linux-x86-low.c (small_jump_insn): New.
     (i386_install_fast_tracepoint_jump_pad): Add arguments for
     trampoline and error message, build a trampoline and issue a small
     jump instruction to it.
     (x86_install_fast_tracepoint_jump_pad): Add arguments for
     trampoline and error message.
     (x86_get_min_fast_tracepoint_insn_len): New.
     (the_low_target): Add call to x86_get_min_fast_tracepoint_insn_len.
     * linux-low.h (struct linux_target_ops): Add arguments to
     install_fast_tracepoint_jump_pad operation, add new operation.
     * linux-low.c (linux_install_fast_tracepoint_jump_pad): Add
     arguments.
     (linux_get_min_fast_tracepoint_insn_len): New function.
     (linux_target_op): Add new operation.
     * tracepoint.c (gdb_trampoline_buffer): New IPA variable.
     (gdb_trampoline_buffer_end): Ditto.
     (gdb_trampoline_buffer_error): Ditto.
     (struct ipa_sym_addresses): Add fields for new IPA variables.
     (symbol_list): Add entries for new IPA variables.
     (struct tracepoint): Add fields to hold the address range of the
     trampoline used by the tracepoint.
     (trampoline_buffer_head): New static variable.
     (trampoline_buffer_tail): Ditto.
     (claim_trampoline_space): New function.
     (have_fast_tracepoint_trampoline_buffer): New function.
     (cmd_qtstart): Return errors in packet reply, fill in trampoline
     fields of tracepoint structure.
     (cmd_qtminftpilen): New function.
     (handle_tracepoint_query): Add response to qTMinFTPILen packet.
     (fast_tracepoint_from_trampoline_address): New function.
     (fast_tracepoint_collecting): Handle trampoline as part of jump
     pad space.
     (set_trampoline_buffer_space): New function.
     (initialize_tracepoint): Initialize new IPA variables.
     * target.h (struct target_ops): Add arguments to
     install_fast_tracepoint_jump_pad operation, add new
     get_min_fast_tracepoint_insn_len operation.
     (target_get_min_fast_tracepoint_insn_len): New.
     (install_fast_tracepoint_jump_pad): Add arguments.
     * server.h (IPA_BUFSIZ): Define.
     * linux-i386-ipa.c: Include extra header files.
     (initialize_fast_tracepoint_trampoline_buffer): New function.
     (initialize_low_tracepoint): Call it.
     * server.h (set_trampoline_buffer_space): Declare.
     (claim_trampoline_space): Ditto.
     (have_fast_tracepoint_trampoline_buffer): Ditto.

     [doc]
     * gdb.texinfo (Create and Delete Tracepoints): Describe what is
     needed to get shorter fast tracepoints.
     (Tracepoint Packets): Document new qTMinFTPILen packet.

     [testsuite]
     * gdb.trace/ftrace.c: New.
     * gdb.trace/ftrace.exp: New.

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