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

# Copyright (C) 2021 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 text 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

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

# Skip this test if Python scripting is not enabled.
if { [skip_python_tests] } { continue }

if ![runto_main] then {
    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"

# Check the unbroken stack.
gdb_test_sequence "bt" "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" "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" "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" "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"
gdb_test_multiple "bt" "backtrace with debugging on" {
    -re "^$gdb_prompt $" {
	pass $gdb_test_name
    }
    -re "\[^\r\n\]+\r\n" {
	exp_continue
    }
}
gdb_test "p 1 + 2 + 3" " = 6" \
    "ensure GDB is still alive"