2011-11-14 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_get_min_fast_tracepoint_insn_len): New.
	(init_remote_ops): Initialize new field.

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

	* 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.
	(clone_fast_tracepoint): Fill in trampoline fields of tracepoint
	structure.
	(install_fast_tracepoint): Ditto, also add error buffer argument.
	(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.

	* gdb.trace/ftrace.c: New.
	* gdb.trace/ftrace.exp: New.

2 files changed, 50 insertions, 0 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index ac38897..02ef07b 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,10 @@
+2011-11-14  Stan Shebs  <stan@codesourcery.com>
+	    Kwok Cheung Yeung  <kcy@codesourcery.com>
+
+	* gdb.texinfo (Create and Delete Tracepoints): Describe what is
+	needed to get shorter fast tracepoints.
+	(Tracepoint Packets): Document new qTMinFTPILen packet.
+
 2011-11-14  Yao Qi  <yao@codesourcery.com>
 
 	* gdb.texinfo (Create and Delete Tracepoints): Describe changed
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index f17c800..0cadc96 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -10378,6 +10378,23 @@ message.
 @value{GDBN} handles arguments to @code{ftrace} exactly as for
 @code{trace}.
 
+On 32-bit x86-architecture systems, fast tracepoints normally need to
+be placed at an instruction that is 5 bytes or longer, but can be
+placed at 4-byte instructions if the low 64K of memory of the target
+program is available to install trampolines.  Some Unix-type systems,
+such as @sc{gnu}/Linux, exclude low addresses from the program's
+address space; but for instance with the Linux kernel it is possible
+to let @value{GDBN} use this area by doing a @command{sysctl} command
+to set the @code{mmap_min_addr} kernel parameter, as in
+
+@example
+sudo sysctl -w vm.mmap_min_addr=32768
+@end example
+
+@noindent
+which sets the low address to 32K, which leaves plenty of room for
+trampolines.  The minimum address should be set to a page boundary.
+
 @item strace @var{location} [ if @var{cond} ]
 @cindex set static tracepoint
 @cindex static tracepoints, setting
@@ -34915,6 +34932,8 @@ encoded).  @value{GDBN} will continue to supply the values of symbols
 @itemx qTfP
 @itemx qTfV
 @itemx QTFrame
+@itemx qTMinFTPILen
+
 @xref{Tracepoint Packets}.
 
 @item qThreadExtraInfo,@var{thread-id}
@@ -35438,6 +35457,30 @@ numbers.
 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
 frame @emph{outside} the given range of addresses (exclusive).
 
+@item qTMinFTPILen
+This packet requests the minimum length of instruction at which a fast
+tracepoint (@pxref{Set Tracepoints}) may be placed.  For instance, on
+the 32-bit x86 architecture, it is possible to use a 4-byte jump, but
+it depends on the target system being able to create trampolines in
+the first 64K of memory, which might or might not be possible for that
+system.  So the reply to this packet will be 4 if it is able to
+arrange for that.
+
+Replies:
+
+@table @samp
+@item 0
+The minimum instruction length is currently unknown.
+@item @var{length}
+The minimum instruction length is @var{length}, where @var{length} is greater
+or equal to 1.  @var{length} is a hexadecimal number.  A reply of 1 means
+that a fast tracepoint may be placed on any instruction regardless of size.
+@item E
+An error has occurred.
+@item
+An empty reply indicates that the request is not supported by the stub.
+@end table
+
 @item QTStart
 Begin the tracepoint experiment.  Begin collecting data from
 tracepoint hits in the trace frame buffer.  This packet supports the