gdb/testsuite: fix readnow detection

The following commit broke the readnow detection in the testsuite:

  commit dfaa040b440084dd73ebd359326752d5f44fc02c
  Date:   Mon Mar 29 18:31:31 2021 -0600

      Remove some "OBJF_READNOW" code from dwarf2_debug_names_index

The testsuite checks if GDB was started with the -readnow flag by
using the 'maintenance print objfiles' command, and looking for the
string 'faked for "readnow"' in the output.  This is implemented in
two helper procs `readnow` (gdb.exp) and `mi_readnow` (mi-support.exp).

The following tests all currently depend on this detection:

  gdb.base/maint.exp
  gdb.cp/nsalias.exp
  gdb.dwarf2/debug-aranges-duplicate-offset-warning.exp
  gdb.dwarf2/dw2-stack-boundary.exp
  gdb.dwarf2/dw2-zero-range.exp
  gdb.dwarf2/gdb-index-nodebug.exp
  gdb.mi/mi-info-sources.exp
  gdb.python/py-symbol.exp
  gdb.rust/traits.exp

The following test also includes detection of 'readnow', but does the
detection itself by checking $::GDBFLAGS for the readnow flag:

  gdb.opt/break-on-_exit.exp

The above commit removed from GDB the code that produced the 'faked
for "readnow"' string, as a consequence the testsuite can no longer
correctly spot when readnow is in use, and many of the above tests
will fail (at least partially).

When looking at the above tests, I noticed that gdb.rust/traits.exp
does call `readnow`, but doesn't actually use the result, so I've
removed the readnow call, this simplifies the next part of this patch
as gdb.rust/traits.exp was the only place an extra regexp was passed
to the readnow call.

Next I have rewritten `readnow` to check the $GDBFLAGS for the
-readnow flag, and removed the `maintenance print objfiles` check.  At
least for all the tests above, when using the readnow board, this is
good enough to get everything passing again.

For the `mi_readnow` proc, I changed this to just call `readnow` from
gdb.exp, I left the mi_readnow name in place - in the future it might
be the case that we want to do some different checks here.

Finally, I updated gdb.opt/break-on-_exit.exp to call the `readnow`
proc.

With these changes, all of the tests listed above now pass correctly
when using the readnow board.

4 files changed, 10 insertions, 53 deletions

diff --git a/gdb/testsuite/gdb.opt/break-on-_exit.exp b/gdb/testsuite/gdb.opt/break-on-_exit.exp
index 7c2fda6..3d18cd7 100644
--- a/gdb/testsuite/gdb.opt/break-on-_exit.exp
+++ b/gdb/testsuite/gdb.opt/break-on-_exit.exp
@@ -36,8 +36,7 @@
 standard_testfile
 
 # See if we have target board readnow.exp or similar.
-if { [lsearch -exact $GDBFLAGS -readnow] != -1 \
-	 || [lsearch -exact $GDBFLAGS --readnow] != -1 } {
+if {[readnow]} {
     untested "--readnever not allowed in combination with --readnow"
     return -1
 }
diff --git a/gdb/testsuite/gdb.rust/traits.exp b/gdb/testsuite/gdb.rust/traits.exp
index aa45e64..949e7cb 100644
--- a/gdb/testsuite/gdb.rust/traits.exp
+++ b/gdb/testsuite/gdb.rust/traits.exp
@@ -43,7 +43,5 @@ if {![runto ${srcfile}:$line]} {
     return -1
 }
 
-set readnow_p [readnow $binfile]
-
 gdb_test "print *td" " = 23.5"
 gdb_test "print *tu" " = 23"
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 008f59b..132d538 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -8553,32 +8553,12 @@ gdb_caching_proc supports_fcf_protection {
   } executable "additional_flags=-fcf-protection=full"]
 }
 
-# Return 1 if symbols were read in using -readnow.  Otherwise, return 0.
+# Return true if symbols were read in using -readnow.  Otherwise,
+# return false.
 
-proc readnow { args } {
-    if { [llength $args] == 1 } {
-	set re [lindex $args 0]
-    } else {
-	set re ""
-    }
-
-    set readnow_p 0
-    # Given the listing from the following command can be very verbose, match
-    # the patterns line-by-line.  This prevents timeouts from waiting for
-    # too much data to come at once.
-    set cmd "maint print objfiles $re"
-    gdb_test_multiple $cmd "" -lbl {
-	-re "\r\n.gdb_index: faked for \"readnow\"" {
-	    # Record the we've seen the above pattern.
-	    set readnow_p 1
-	    exp_continue
-	}
-	-re -wrap "" {
-	    # We don't care about any other input.
-	}
-    }
-
-    return $readnow_p
+proc readnow { } {
+    return [expr {[lsearch -exact $::GDBFLAGS -readnow] != -1
+		  || [lsearch -exact $::GDBFLAGS --readnow] != -1}]
 }
 
 # Return index name if symbols were read in using an index.
diff --git a/gdb/testsuite/lib/mi-support.exp b/gdb/testsuite/lib/mi-support.exp
index 18a2a04..2dccb89 100644
--- a/gdb/testsuite/lib/mi-support.exp
+++ b/gdb/testsuite/lib/mi-support.exp
@@ -671,32 +671,12 @@ proc mi_gdb_load { arg } {
     return 0
 }
 
-# Return 1 if symbols were read in using -readnow.  Otherwise, return 0.
-# Based on readnow from lib/gdb.exp.
+# Return true if symbols were read in using -readnow.  Otherwise,
+# return false.
 
 proc mi_readnow { args } {
-    global mi_gdb_prompt
-
-    if { [llength $args] == 1 } {
-	set re [lindex $args 0]
-    } else {
-	set re ""
-    }
-
-    set readnow_p 0
-    set cmd "maint print objfiles $re"
-    send_gdb "$cmd\n"
-    gdb_expect {
-	-re ".gdb_index: faked for ..readnow.." {
-	    # Record that we've seen the above pattern.
-	    set readnow_p 1
-	    exp_continue
-	}
-	-re "\\^done\r\n$mi_gdb_prompt$" {
-	}
-    }
-
-    return $readnow_p
+    # Just defer to gdb.exp.
+    return [readnow]
 }
 
 # mi_gdb_test COMMAND [PATTERN [MESSAGE [IPATTERN]]] -- send a command to gdb;