gdb: new 'maint print frame-id' command

When debugging a certain class of GDB bug, I often end up wanting to
know what GDB thinks the frame-id is in a particular frame.  It's
not too hard to pull this from some debug output, but I thought it
might be nice if there was a maintenance command that could tell us.

This commit adds 'maint print frame-id' which prints the frame-id of
the currently selected frame.  You can also pass a frame level number
to find the frame-id for a specific frame.

There's a new test too.

1 files changed, 68 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.base/maint-print-frame-id.exp b/gdb/testsuite/gdb.base/maint-print-frame-id.exp
new file mode 100644
index 0000000..395927a
--- /dev/null
+++ b/gdb/testsuite/gdb.base/maint-print-frame-id.exp
@@ -0,0 +1,68 @@
+# Copyright 2022 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test the 'maint print frame-id' command.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile \
+	 $srcfile {debug}]} {
+    return -1
+}
+
+if ![runto_main] then {
+    return -1
+}
+
+gdb_breakpoint foo
+gdb_continue_to_breakpoint "run to foo"
+
+proc get_frame_id { level } {
+    set id "**unknown**"
+
+    gdb_test_multiple "maint print frame-id ${level}" "" {
+	-re "^maint print frame-id\[^\r\n\]+\r\n" {
+	    exp_continue
+	}
+
+	-wrap -re "^frame-id for frame #\[0-9\]+: (\[^\r\n\]+)" {
+	    set id $expect_out(1,string)
+	    pass $gdb_test_name
+	}
+    }
+
+    return $id
+}
+
+# Get the frame-id for each frame using the frame level.
+array set ids {}
+with_test_prefix "get id by level" {
+    for { set i 0 } { $i < 4 } { incr i } {
+	set ids($i) [get_frame_id $i]
+    }
+}
+
+# Now get the frame-id of the currently selected frame, and check it
+# matches the frame-id we got earlier.  Then move up the stack,
+# selecting a new frame.
+for { set i 0 } { $i < 4 } { incr i } {
+    with_test_prefix "frame $i is current" {
+	set id [get_frame_id ""]
+	gdb_assert { [string equal $id $ids($i)] } \
+	    "check frame-id matches"
+    }
+    gdb_test "up" ".*" \
+	"move up from frame $i"
+}