Locate executables on remote stubs without multiprocess extensions

This commit allows GDB to determine filenames of main executables
when debugging using remote stubs without multiprocess extensions.
The qXfer:exec-file:read packet is extended to allow an empty
annex, with the meaning that the remote stub should supply the
filename of whatever it thinks is the current process.

gdb/ChangeLog:

	* remote.c (remote_add_inferior): Call exec_file_locate_attach
	for fake PIDs as well as real ones.
	(remote_pid_to_exec_file): Send empty annex if PID is fake.

gdb/doc/ChangeLog:

	* gdb.texinfo (General Query Packets): Document
	qXfer:exec-file:read with empty annex.

gdb/gdbserver/ChangeLog:

	* server.c (handle_qxfer_exec_file): Use current process
	if annex is empty.

2 files changed, 25 insertions, 5 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index c33f90a10c3..94146b8f48b 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2015-05-12  Gary Benson <gbenson@redhat.com>
+
+	* server.c (handle_qxfer_exec_file): Use current process
+	if annex is empty.
+
 2015-05-08  Sandra Loosemore  <sandra@codesourcery.com>
 
 	* linux-nios2-low.c: Include elf/common.h.  Adjust comments.
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index 3f9bb8938d6..174ab398b0b 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -1146,17 +1146,32 @@ handle_qxfer_exec_file (const char *const_annex,
 			gdb_byte *readbuf, const gdb_byte *writebuf,
 			ULONGEST offset, LONGEST len)
 {
-  char *annex, *file;
+  char *file;
   ULONGEST pid;
   int total_len;
 
   if (the_target->pid_to_exec_file == NULL || writebuf != NULL)
     return -2;
 
-  annex = alloca (strlen (const_annex) + 1);
-  strcpy (annex, const_annex);
-  annex = unpack_varlen_hex (annex, &pid);
-  if (annex[0] != '\0' || pid == 0)
+  if (const_annex[0] == '\0')
+    {
+      if (current_thread == NULL)
+	return -1;
+
+      pid = pid_of (current_thread);
+    }
+  else
+    {
+      char *annex = alloca (strlen (const_annex) + 1);
+
+      strcpy (annex, const_annex);
+      annex = unpack_varlen_hex (annex, &pid);
+
+      if (annex[0] != '\0')
+	return -1;
+    }
+
+  if (pid <= 0)
     return -1;
 
   file = (*the_target->pid_to_exec_file) (pid);