binutils-gdb/gdb/testsuite/gdb.base/inline-frame-cycle-unwind.exp

# Copyright (C) 2021-2024 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/>.

# This test checks for an edge case when unwinding inline frames which
# occur towards the older end of the stack when the stack ends with a
# cycle.  Consider this well formed stack:
#
#   main -> normal_frame -> inline_frame
#
# Now consider that, for whatever reason, the stack unwinding of
# "normal_frame" becomes corrupted, such that the stack appears to be
# this:
#
#   .-> normal_frame -> inline_frame
#   |      |
#   '------'
#
# When confronted with such a situation we would expect GDB to detect
# the stack frame cycle and terminate the backtrace at the first
# instance of "normal_frame" with a message:
#
#   Backtrace stopped: previous frame identical to this frame (corrupt stack?)
#
# However, at one point there was a bug in GDB's inline frame
# mechanism such that the fact that "inline_frame" was inlined into
# "normal_frame" would cause GDB to trigger an assertion.
#
# This test makes use of a Python unwinder which can fake the cyclic
# stack cycle, further the test sets up multiple levels of normal and
# inline frames.  At the point of testing the stack looks like this:
#
#   main -> normal_func -> inline_func -> normal_func -> inline_func -> normal_func -> inline_func
#
# Where "normal_func" is a normal frame, and "inline_func" is an inline frame.
#
# The python unwinder is then used to force a stack cycle at each
# "normal_func" frame in turn, we then check that GDB can successfully unwind
# the stack.

standard_testfile

require allow_python_tests

if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
    return -1
}

if {![runto_main]} {
    return 0
}

set pyfile [gdb_remote_download host ${srcdir}/${subdir}/${testfile}.py]

# Run to the breakpoint where we will carry out the test.
gdb_breakpoint [gdb_get_line_number "Break here"]
gdb_continue_to_breakpoint "stop at test breakpoint"

# Load the script containing the unwinder, this must be done at the
# testing point as the script will examine the stack as it is loaded.
gdb_test_no_output "source ${pyfile}"\
    "import python scripts"

# Test with and without filters.
foreach bt_cmd { "bt" "bt -no-filters" } {
    with_test_prefix "$bt_cmd" {

	# Check the unbroken stack.
	gdb_test_sequence "$bt_cmd" "backtrace when the unwind is left unbroken" {
	    "\\r\\n#0 \[^\r\n\]* inline_func \\(\\) at "
	    "\\r\\n#1 \[^\r\n\]* normal_func \\(\\) at "
	    "\\r\\n#2 \[^\r\n\]* inline_func \\(\\) at "
	    "\\r\\n#3 \[^\r\n\]* normal_func \\(\\) at "
	    "\\r\\n#4 \[^\r\n\]* inline_func \\(\\) at "
	    "\\r\\n#5 \[^\r\n\]* normal_func \\(\\) at "
	    "\\r\\n#6 \[^\r\n\]* main \\(\\) at "
	}

	with_test_prefix "cycle at level 5" {
	    # Arrange to introduce a stack cycle at frame 5.
	    gdb_test_no_output "python stop_at_level=5"
	    gdb_test "maint flush register-cache" \
		"Register cache flushed\\."
	    gdb_test_lines "$bt_cmd" "backtrace when the unwind is broken at frame 5" \
		[multi_line \
		    "#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
		    "#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
		    "#2 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
		    "#3 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
		    "#4 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
		    "#5 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
		    "Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"]
	}

	with_test_prefix "cycle at level 3" {
	    # Arrange to introduce a stack cycle at frame 3.
	    gdb_test_no_output "python stop_at_level=3"
	    gdb_test "maint flush register-cache" \
		"Register cache flushed\\."
	    gdb_test_lines "$bt_cmd" "backtrace when the unwind is broken at frame 3" \
		[multi_line \
		    "#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
		    "#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
		    "#2 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
		    "#3 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
		    "Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"]
	}

	with_test_prefix "cycle at level 1" {
	    # Arrange to introduce a stack cycle at frame 1.
	    gdb_test_no_output "python stop_at_level=1"
	    gdb_test "maint flush register-cache" \
		"Register cache flushed\\."
	    gdb_test_lines "$bt_cmd" "backtrace when the unwind is broken at frame 1" \
		[multi_line \
		    "#0 \[^\r\n\]* inline_func \\(\\) at \[^\r\n\]+" \
		    "#1 \[^\r\n\]* normal_func \\(\\) at \[^\r\n\]+" \
		    "Backtrace stopped: previous frame identical to this frame \\(corrupt stack\\?\\)"]
	}

	# Flush the register cache (which also flushes the frame cache) so we
	# get a full backtrace again, then switch on frame debugging and try
	# to back trace.  At one point this triggered an assertion.
	gdb_test "maint flush register-cache" \
	    "Register cache flushed\\." ""
	gdb_test_no_output "set debug frame 1"
	set ok 1
	gdb_test_multiple "$bt_cmd" "backtrace with debugging on" {
	    -re "^$gdb_prompt $" {
		gdb_assert { $ok } $gdb_test_name
	    }
	    -re "Python Exception <class 'gdb.error'>: \[^\r\n\]*\r\n" {
		set ok 0
		exp_continue
	    }
	    -re "\[^\r\n\]+\r\n" {
		exp_continue
	    }
	}
	gdb_test "p 1 + 2 + 3" " = 6" \
	    "ensure GDB is still alive"

	# Prepare for the next iteration of the test loop
	gdb_test_no_output "set debug frame 0"
	gdb_test_no_output "python stop_at_level=None"
	    gdb_test "maint flush register-cache" \
		"Register cache flushed\\." "maint flush register-cache at (loop end)"
    }
}