[PATCH] Do not record a rejected target description

[Tom Tromey <tromey@adacore.com>]

When connecting to a certain target, gdb issues a warning about the
target description:

    (gdb) target remote localhost:7947
    Remote debugging using localhost:7947
    warning: Architecture rejected target-supplied description

If you then kill the inferior and change the exec-file, this will
happen:

    (gdb) file bar
    Architecture of file not recognized.

After this, debugging doesn't work very well.

What happens here is that, despite the warning,
target_find_description records the downloaded description in the
target_desc_info.  Then the "file" command ends up calling
set_gdbarch_from_file, which uses that description.

It seems to me that, because the architecture rejected the
description, it should not be used.  That is what this patch
implements.
---
 gdb/target-descriptions.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gdb/target-descriptions.c b/gdb/target-descriptions.c
index 1a451c79b82..38d0b3f8c7d 100644
--- a/gdb/target-descriptions.c
+++ b/gdb/target-descriptions.c
@@ -565,7 +565,10 @@ target_find_description (void)
 
       info.target_desc = tdesc_info->tdesc;
       if (!gdbarch_update_p (info))
-	warning (_("Architecture rejected target-supplied description"));
+	{
+	  warning (_("Architecture rejected target-supplied description"));
+	  tdesc_info->tdesc = nullptr;
+	}
       else
 	{
 	  struct tdesc_arch_data *data;
-- 
2.38.1