Re: [PATCH 3/3][gdb/testsuite] Warn about leaked global array

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

* Andrew Burgess <andrew.burgess@embecosm.com> [2020-06-02 16:38:30 +0100]:

> * Tom de Vries <tdevries@suse.de> [2020-05-19 18:30:06 +0200]:
> 
> > Hi,
> > 
> > A variable name cannot be used both as scalar and array without an
> > intermediate unset.  Trying to do so will result in tcl errors, for
> > example, for:
> > ...
> >   set var "bla"
> >   set var(1) "bla"
> > ...
> > we get:
> > ...
> >   can't set "var(1)": variable isn't array
> > ...
> > and for the reverse statement order we get:
> > ...
> >   can't set "var": variable is array
> > ...
> > 
> > So, since a global name in one test-case can leak to another
> > test-case, setting a global name in one test-case can result in
> > a tcl error in another test-case that reuses the name in a different
> > way.
> > 
> > Warn about leaking a global array from a test-case.
> > 
> > Also, add a possibility to skip the warning in a given test-case using
> > variable gdb_skip_check_global_vars, and use it in gdb.mi/mi2-var-child.exp
> > and gdb.mi/mi-var-cp.exp.
> > 
> > Tested on x86_64-linux.
> > 
> > Any comments?
> 
> If we're going to add code to loop over all globals anyway, then why
> not, instead of warning about bad cases, and then wrapping tests in a
> namespace, just have this code "fix" the leaked globals by deleting
> them?
> 
> My thinking is that any global that exists when we start a test should
> continue to exist at the end of the test.  Any other global should
> just be unset when the test script finishes.
> 
> If there really is some global state that is lazily created by a
> particular test script then (a) this seems like a bug anyway, and (b)
> this is easy to fix by giving it an earlier creation / initialisation.
> 
> In this way, folk can just write test scripts, dump their junk all
> over the global namespace as they like, and we'll just clean up for
> them.
> 
> Thoughts?

Here's a really quick patch implementing the idea above.  It needs
cleaning up and commenting, etc, but it passes the testsuite with no
regressions, and taking a look at its debug output, I can see it
deleting some of the problem global arrays that are causing issues.

What do you think of this approach?

Thanks,
Andrew

----

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 444cea01c36..c983c9cc172 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5094,7 +5094,11 @@ set banned_procedures { strace }
 # if the banned variables and procedures are already traced.
 set banned_traced 0
 
+array set known_globals {}
+
 proc gdb_init { test_file_name } {
+    global known_globals
+
     # Reset the timeout value to the default.  This way, any testcase
     # that changes the timeout value without resetting it cannot affect
     # the timeout used in subsequent testcases.
@@ -5196,13 +5200,27 @@ proc gdb_init { test_file_name } {
     global gdb_instances
     set gdb_instances 0
 
-    return [default_gdb_init $test_file_name]
+    set result [default_gdb_init $test_file_name]
+
+    foreach varname [info globals] {
+	set known_globals($varname) 1
+    }
+
+    return $result
 }
 
 proc gdb_finish { } {
     global gdbserver_reconnect_p
     global gdb_prompt
     global cleanfiles
+    global known_globals
+
+    foreach varname [info globals] {
+	if {![info exists known_globals($varname)]} {
+	    verbose -log "APB: Deleting '$varname'"
+	    upvar 0 unset $varname
+	}
+    }
 
     # Exit first, so that the files are no longer in use.
     gdb_exit