bpo-32962: Fix test_gdb failure in debug build with -mcet -fcf-protection -O0 (GH-9656)

When Python is built with the intel control-flow protection flags, -mcet -fcf-protection, gdb is not able to read the stack without actually jumping inside the function. This means an extra 'next' command is required to make the $pc (program counter) enter the function and make the stack of the function exposed to gdb. Co-Authored-By: Marcel Plch <gmarcel.plch@gmail.com> (cherry picked from commit 9b7c74c) (cherry picked from commit 79d2133) Co-authored-by: Victor Stinner <vstinner@redhat.com>

Author: miss-islington

Lib/test/test_gdb.py

@@ -54,6 +54,23 @@ def get_gdb_version():
 
 PYTHONHASHSEED = '123'
 
+
+def cet_protection():
+ cflags = sysconfig.get_config_var('CFLAGS')
+ if not cflags:
+ return False
+ flags = cflags.split()
+ # True if "-mcet -fcf-protection" options are found, but false
+ # if "-fcf-protection=none" or "-fcf-protection=return" is found.
+ return (('-mcet' in flags)
+ and any((flag.startswith('-fcf-protection')
+ and not flag.endswith(("=none", "=return")))
+ for flag in flags))
+
+# Control-flow enforcement technology
+CET_PROTECTION = cet_protection()
+
+
 def run_gdb(*args, **env_vars):
  """Runs gdb in --batch mode with the additional arguments given by *args.
 
@@ -162,6 +179,12 @@ def get_stack_trace(self, source=None, script=None,
  commands += ['set print entry-values no']
 
  if cmds_after_breakpoint:
+ if CET_PROTECTION:
+ # bpo-32962: When Python is compiled with -mcet
+ # -fcf-protection, function arguments are unusable before
+ # running the first instruction of the function entry point.
+ # The 'next' command makes the required first step.
+ commands += ['next']
  commands += cmds_after_breakpoint
  else:
  commands += ['backtrace']
@@ -869,9 +892,17 @@ def __init__(self):
  id("first break point")
  l = MyList()
  ''')
+ cmds_after_breakpoint = ['break wrapper_call', 'continue']
+ if CET_PROTECTION:
+ # bpo-32962: same case as in get_stack_trace():
+ # we need an additional 'next' command in order to read
+ # arguments of the innermost function of the call stack.
+ cmds_after_breakpoint.append('next')
+ cmds_after_breakpoint.append('py-bt')
+
  # Verify with "py-bt":
  gdb_output = self.get_stack_trace(cmd,
- cmds_after_breakpoint=['break wrapper_call', 'continue', 'py-bt'])
+ cmds_after_breakpoint=cmds_after_breakpoint)
  self.assertRegex(gdb_output,
  r"<method-wrapper u?'__init__' of MyList object at ")
 

Misc/NEWS.d/next/Tests/2018-05-10-16-59-15.bpo-32962.S-rcIN.rst

@@ -0,0 +1 @@
+Fixed test_gdb when Python is compiled with flags -mcet -fcf-protection -O0.