From df5bc734f2dcd07ed3261cd679743924e8962439 Mon Sep 17 00:00:00 2001 From: Magne Hov Date: Thu, 3 Jun 2021 21:20:30 +0100 Subject: gdb: fix eval.c assert during inferior exit event Evaluating expressions from within an inferior exit event handler can cause a crash: echo "int main() { return 0; }" > repro.c gcc -g repro.c -o repro ./gdb -q --ex "set language c++" --ex "python gdb.events.exited.connect(lambda _: gdb.execute('set \$_a=0'))" --ex "run" repro Reading symbols from repro... Starting program: /home/mhov/repos/binutils-gdb-master/install-bad/bin/repro [Inferior 1 (process 1974779) exited normally] ../../gdb/thread.c:72: internal-error: thread_info* inferior_thread(): Assertion `current_thread_ != nullptr' failed. A problem internal to GDB has been detected, further debugging may prove unreliable. Quit this debugging session? (y or n) [answered Y; input not from terminal] This is a bug, please report it. For instructions, see: . Backtrace 0 in internal_error of ../../gdbsupport/errors.cc:51 1 in inferior_thread of ../../gdb/thread.c:72 2 in expression::evaluate of ../../gdb/eval.c:98 3 in evaluate_expression of ../../gdb/eval.c:115 4 in set_command of ../../gdb/printcmd.c:1502 5 in do_const_cfunc of ../../gdb/cli/cli-decode.c:101 6 in cmd_func of ../../gdb/cli/cli-decode.c:2181 7 in execute_command of ../../gdb/top.c:670 ... 22 in python_inferior_exit of ../../gdb/python/py-inferior.c:182 In `expression::evaluate (...)' there is a call to `inferior_thread ()' that is guarded by `target_has_execution ()': struct value * expression::evaluate (struct type *expect_type, enum noside noside) { gdb::optional stack_temporaries; if (target_has_execution () && language_defn->la_language == language_cplus && !thread_stack_temporaries_enabled_p (inferior_thread ())) stack_temporaries.emplace (inferior_thread ()); The `target_has_execution ()' guard maps onto `inf->pid' and the `inferior_thread ()' call assumes that `current_thread_' is set to something meaningful: struct thread_info* inferior_thread (void) { gdb_assert (current_thread_ != nullptr); return current_thread_; } In other words, it is assumed that if `inf->pid' is set then `current_thread_' must also be set. This does not hold at the point where inferior exit observers are notified: - `generic_mourn_inferior (...)' - `switch_to_no_thread ()' - `current_thread_ = nullptr;' - `exit_inferior (...)' - `gdb::observers::inferior_exit.notify (...)' - `inf->pid = 0' The inferior exit notification means that a Python handler can get a chance to run while `current_thread' has been cleared and the `inf->pid' has not been cleared. Since the Python handler can call any GDB command with `gdb.execute(...)' (in my case `gdb.execute("set $_a=0")' we can end up evaluating expressions and asserting in `evaluate_subexp (...)'. This patch adds a test in `evaluate_subexp (...)' to check the global `inferior_ptid' which is reset at the same time as `current_thread_'. Checking `inferior_ptid' at the same time as `target_has_execution ()' seems to be a common pattern: $ git grep -n -e inferior_ptid --and -e target_has_execution gdb/breakpoint.c:2998: && (inferior_ptid == null_ptid || !target_has_execution ())) gdb/breakpoint.c:3054: && (inferior_ptid == null_ptid || !target_has_execution ())) gdb/breakpoint.c:4587: if (inferior_ptid == null_ptid || !target_has_execution ()) gdb/infcmd.c:360: if (inferior_ptid != null_ptid && target_has_execution ()) gdb/infcmd.c:2380: /* FIXME: This should not really be inferior_ptid (or target_has_execution). gdb/infrun.c:3438: if (!target_has_execution () || inferior_ptid == null_ptid) gdb/remote.c:11961: if (!target_has_execution () || inferior_ptid == null_ptid) gdb/solib.c:725: if (target_has_execution () && inferior_ptid != null_ptid) The testsuite has been run on 5.4.0-59-generic x86_64 GNU/Linux: - Ubuntu 20.04.1 LTS - gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 - DejaGnu version 1.6.2 - Expect version 5.45.4 - Tcl version 8.6 - Native configuration: x86_64-pc-linux-gnu - Target: unix Results show a few XFAIL in gdb.threads/attach-many-short-lived-threads.exp. The existing py-events.exp tests are skipped for native-gdbserver and fail for native-extended-gdbserver, but the new tests pass with native-extended-gdbserver when run without the existing tests. gdb/ChangeLog: 2021-06-03 Magne Hov PR python/27841 * eval.c (expression::evaluate): Check inferior_ptid. gdb/testsuite/ChangeLog: 2021-06-03 Magne Hov PR python/27841 * gdb.python/py-events.exp: Extend inferior exit tests. * gdb.python/py-events.py: Print inferior exit PID. --- gdb/eval.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'gdb/eval.c') diff --git a/gdb/eval.c b/gdb/eval.c index 1b3c974..659493c 100644 --- a/gdb/eval.c +++ b/gdb/eval.c @@ -93,7 +93,7 @@ struct value * expression::evaluate (struct type *expect_type, enum noside noside) { gdb::optional stack_temporaries; - if (target_has_execution () + if (target_has_execution () && inferior_ptid != null_ptid && language_defn->la_language == language_cplus && !thread_stack_temporaries_enabled_p (inferior_thread ())) stack_temporaries.emplace (inferior_thread ()); -- cgit v1.1