[RFA] Auto set gnutarget when bfd_check_format_matches get bfd_error_file_ambiguously_recognized

[Hui Zhu <teawater at gmail dot com>]

Hello,

In sometime before, I add a patch to make GDB show some help message
when bfd_check_format_matches get
bfd_error_file_ambiguously_recognized, like:
"/home/teawater/Desktop/vmlinux": not in executable format: File
format is ambiguous.
Matching formats: elf64-bigmips elf64-tradbigmips.
Use "set gnutarget format-name" to specify the format.

But to really open this file, user need set gnutarget elf64-bigmips
and file /home/teawater/Desktop/vmlinux.

So I add a patch to auto do it. Like:
warning: "/home/teawater/Desktop/vmlinux": not in executable format:
File format is ambiguous.
Matching formats: elf64-bigmips elf64-tradbigmips.
Use "set gnutarget format-name" to specify the format.
warning: Auto set it to "elf64-bigmips".
Reading symbols from /home/teawater/Desktop/vmlinux...done.

Please help me review it.

Thanks,
Hui

2010-06-30  Hui Zhu  <teawater@gmail.com>

	* exec.c (exec_file_attach): Add code to handle
	bfd_error_file_ambiguously_recognized.
---
 exec.c |   22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

--- a/exec.c
+++ b/exec.c
@@ -217,6 +217,7 @@ exec_file_attach (char *filename, int fr
       struct target_section *sections = NULL, *sections_end = NULL;
       char **matching;

+retry:
       scratch_chan = openp (getenv ("PATH"), OPF_TRY_CWD_FIRST, filename,
 		   write_files ? O_RDWR | O_BINARY : O_RDONLY | O_BINARY,
 			    &scratch_pathname);
@@ -253,12 +254,27 @@ exec_file_attach (char *filename, int fr

       if (!bfd_check_format_matches (exec_bfd, bfd_object, &matching))
 	{
+          bfd_error_type error_tag = bfd_get_error ();
+
 	  /* Make sure to close exec_bfd, or else "run" might try to use
 	     it.  */
 	  exec_close ();
-	  error (_("\"%s\": not in executable format: %s"),
-		 scratch_pathname,
-		 gdb_bfd_errmsg (bfd_get_error (), matching));
+
+          if (error_tag != bfd_error_file_ambiguously_recognized
+              || matching == NULL)
+	    error (_("\"%s\": not in executable format: %s"),
+		   scratch_pathname,
+		   gdb_bfd_errmsg (error_tag, matching));
+          else
+            {
+              set_gnutarget (*matching);
+	      warning (_("\"%s\": not in executable format: %s"),
+		       scratch_pathname,
+		       gdb_bfd_errmsg (error_tag, matching));
+              warning (_("Auto set it to \"%s\"."), gnutarget);
+              do_cleanups (cleanups);
+              goto retry;
+            }
 	}

       /* FIXME - This should only be run for RS6000, but the ifdef is a poor