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.

1 files changed, 33 insertions, 12 deletions

diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index 2f0b6f5e929..a4e3a220554 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -7109,10 +7109,12 @@ static const int i386_record_regmap[] =
 };
 
 /* Check that the given address appears suitable for a fast
-   tracepoint, which on x86 means that we need an instruction of at
+   tracepoint, which on x86-64 means that we need an instruction of at
    least 5 bytes, so that we can overwrite it with a 4-byte-offset
    jump and not have to worry about program jumps to an address in the
-   middle of the tracepoint jump.  Returns 1 if OK, and writes a size
+   middle of the tracepoint jump.  On x86, it may be possible to use
+   4-byte jumps with a 2-byte offset to a trampoline located in the
+   bottom 64 KiB of memory.  Returns 1 if OK, and writes a size
    of instruction to replace, and 0 if not, plus an explanatory
    string.  */
 
@@ -7123,10 +7125,26 @@ i386_fast_tracepoint_valid_at (struct gdbarch *gdbarch,
   int len, jumplen;
   static struct ui_file *gdb_null = NULL;
 
-  /* This is based on the target agent using a 4-byte relative jump.
-     Alternate future possibilities include 8-byte offset for x86-84,
-     or 3-byte jumps if the program has trampoline space close by.  */
-  jumplen = 5;
+  /*  Ask the target for the minimum instruction length supported.  */
+  jumplen = target_get_min_fast_tracepoint_insn_len ();
+
+  if (jumplen < 0)
+    {
+      /* If the target does not support the get_min_fast_tracepoint_insn_len
+	 operation, assume that fast tracepoints will always be implemented
+	 using 4-byte relative jumps on both x86 and x86-64.  */
+      jumplen = 5;
+    }
+  else if (jumplen == 0)
+    {
+      /* If the target does support get_min_fast_tracepoint_insn_len but
+	 returns zero, then the IPA has not loaded yet.  In this case,
+	 we optimistically assume that truncated 2-byte relative jumps
+	 will be available on x86, and compensate later if this assumption
+	 turns out to be incorrect.  On x86-64 architectures, 4-byte relative
+	 jumps will always be used.  */
+      jumplen = (register_size (gdbarch, 0) == 8) ? 5 : 4;
+    }
 
   /* Dummy file descriptor for the disassembler.  */
   if (!gdb_null)
@@ -7134,6 +7152,9 @@ i386_fast_tracepoint_valid_at (struct gdbarch *gdbarch,
 
   /* Check for fit.  */
   len = gdb_print_insn (gdbarch, addr, gdb_null, NULL);
+  if (isize)
+    *isize = len;
+
   if (len < jumplen)
     {
       /* Return a bit of target-specific detail to add to the caller's
@@ -7144,12 +7165,12 @@ i386_fast_tracepoint_valid_at (struct gdbarch *gdbarch,
 			   len, jumplen);
       return 0;
     }
-
-  if (isize)
-    *isize = len;
-  if (msg)
-    *msg = NULL;
-  return 1;
+  else
+    {
+      if (msg)
+	*msg = NULL;
+      return 1;
+    }
 }
 
 static int