Re: [PATCH] Fix the crash at the end of the runtest

[Andrew Burgess <andrew.burgess@embecosm.com>]

Here's my proposed fix, along with an explanation of what's going on.

Thanks,
Andrew

---

commit c6d3cd6e265dd39a27d13428eba48df8c1d50c95
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Thu Jul 22 14:07:15 2021 +0100

    gdb/testsuite: don't error when trying to unset last_spawn_tty_name
    
    In spawn_capture_tty_name (lib/gdb.exp) we either set or unset
    last_spawn_tty_name depending on whether spawn_out exists or not.
    
    One situation that might cause spawn_out to not exists is if the spawn
    function is called with the argument -leaveopen, which is how it is
    called when processes are created as part of a pipeline, the created
    process has no tty, instead its output is written to a file
    descriptor.
    
    If a pipe line is created consisting of multiple processes then there
    will be multiple sequential calls to spawn, all using -leaveopen.  The
    first of these calls is fine, no spawn_out is set, and so in
    spawn_capture_tty_name we unset last_spawn_tty_name.  However, on the
    second call to spawn there is still no spawn_out and so in
    spawn_capture_tty_name we again try to unset last_spawn_tty_name, this
    now throws an error.
    
    Fix this issue by using -nocomplain with the call to unset in
    spawn_capture_tty_name.
    
    Before this commit I was seeing gdb.base/gnu-debugdata.exp report 1
    pass, and 1 unsupported test.  After this commit I now see 16 passes
    from this test script.

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index e79e0622f9d..8712669bdce 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -2032,7 +2032,7 @@ proc spawn_capture_tty_name { args } {
     if { [info exists spawn_out] } {
 	set ::last_spawn_tty_name $spawn_out(slave,name)
     } else {
-	unset ::last_spawn_tty_name
+	unset -nocomplain ::last_spawn_tty_name
     }
     return $result
 }