Re: [PATCH 2/2] Implement target async for Windows

[Tom Tromey <tromey@adacore.com>]

>>>>> "Jon" == Jon Turney <jon.turney@dronecode.org.uk> writes:

>> Thread 1 "gdb" received signal SIGSEGV, Segmentation fault.
>> ops=ops@entry=0x100abfca0 <serial_event_ops>, open_name=open_name@entry=0x0) at ../../gdb/serial.c:249
>> 249       if (!serial_logfile.empty ())
>> (top-gdb) p serial_logfile
>> $1 = <error reading variable: Cannot access memory at address 0xffffffffffffffe8>
>> (top-gdb) bt
>> #0  0x000000010071e755 in serial_open_ops_1 (ops=ops@entry=0x100abfca0 <serial_event_ops>, open_name=open_name@entry=0x0) at ../../gdb/serial.c:249
>> #1  0x000000010071ec77 in serial_open_ops (ops=ops@entry=0x100abfca0 <serial_event_ops>) at ../../gdb/serial.c:267
>> #2  0x000000010071d0ac in make_serial_event () at ../../gdb/ser-event.c:164
>> #3  0x0000000100810f9e in windows_nat_target::windows_nat_target (this=0x100cdf2e0 <the_windows_nat_target>) at ../../gdb/windows-nat.c:406
>> #4  0x00000001009d77f0 in __static_initialization_and_destruction_0 (__initialize_p=1, __priority=65535) at ../../gdb/windows-nat.c:390
>> #5  _GLOBAL__sub_I__ZN18windows_nat_targetC2Ev () at ../../gdb/windows-nat.c:3311
>> #6  0x00007fff152a6582 in do_global_ctors (force=0, in_pfunc=0x1009d8700 <___CTOR_LIST__>) at ../../../../src/winsup/cygwin/dcrt0.cc:78
>> #7  __main () at ../../../../src/winsup/cygwin/dcrt0.cc:1084
>> #8  0x00000001009cd7d0 in main (argc=1, argv=0x7ffffcc50) at ../../gdb/gdb.c:25

Jon> This looks like an problem with static object construction ordering:
Jon> the serial_logfile object needs to be constructed before before 
Jon> the_windows_nat_target object, but nothing enforces that, currently.

Ugh...

Jon> Attached is a patch I wrote to verify the issue, and applying it fixes
Jon> the crash for me, but I'm sure there is a more elegant solution out
Jon> there...

It seems to me that serial.c is blameless and that windows-nat should
probably not have a static initializer with dependencies.

Could you try this change instead?

Tom

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index ab94de03bbf..ecd5cf7e3fb 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -385,7 +385,9 @@ struct windows_nat_target final : public x86_nat_target<inf_child_target>
   bool m_is_async = false;
 };
 
-static windows_nat_target the_windows_nat_target;
+/* This is a pointer and not a global specifically to avoid a C++
+   "static initializer fiasco" situation.  */
+static windows_nat_target *the_windows_nat_target;
 
 static void
 check (BOOL ok, const char *file, int line)
@@ -621,7 +623,7 @@ windows_nat_target::delete_thread (ptid_t ptid, DWORD exit_code,
 		target_pid_to_str (ptid).c_str (),
 		(unsigned) exit_code);
 
-  ::delete_thread (find_thread_ptid (&the_windows_nat_target, ptid));
+  ::delete_thread (find_thread_ptid (the_windows_nat_target, ptid));
 
   auto iter = std::find_if (windows_process.thread_list.begin (),
 			    windows_process.thread_list.end (),
@@ -3119,7 +3121,8 @@ _initialize_windows_nat ()
      calling x86_set_debug_register_length function
      in processor windows specific native file.  */
 
-  add_inf_child_target (&the_windows_nat_target);
+  the_windows_nat_target = new windows_nat_target;
+  add_inf_child_target (the_windows_nat_target);
 
 #ifdef __CYGWIN__
   cygwin_internal (CW_SET_DOS_FILE_WARNING, 0);